Ferromagnetism

Motivated by exploring spin-orbit coupled magnetism in 5d-based transition metal oxides (TMOs) beyond the iridates, we present a powder inelastic neutron scattering study of magnetic excitations in Ba2FeReO6-a member of the double perovskite family of materials which exhibit half-metallic behavior and high Curie temperatures Tc. We find clear evidence of two well-defined dispersing magnetic modes in its low temperature ferrimagnetic state. We develop a local moment model, which incorporates the interaction of Fe spins with spin-orbital locked magnetic moments on Re, and show that it captures our experimental observations. This allows us to extract moment sizes and exchange couplings, explain the magnitude of Tc, and to infer that magneto-structural locking terms are weak. Our study further opens up Re-based compounds as model systems to explore the interplay of strong correlations and spin-orbit coupling in 5d TMOs.

We study the dependence of magnetic interactions and Curie temperature in Ni (1+x) MnSb system on the Ni concentration within the framework of the density-functional theory. The calculation of the exchange parameters is based on the super-cell and frozen-magnon approaches. The Curie temperatures, TC , are calculated within the random-phase approximation. In agreement with experiment we obtain decrease of the Curie temperature with increasing Ni content.

Magnetic properties are studied on Rb clusters generated in the cages of zeolite A (framework type code LTA), where the cages with an inside diameter of $11 Å are arrayed in a simple cubic structure. When the average number of s-electrons per cluster, n, is larger than $4, ferromagnetic properties are newly observed at low temperatures. The Curie temperature is estimated to be $3.5 K at n ¼ 5.0 from the Arrott-plot analysis. The magnetic susceptibility shows Curie-Weiss law with a negative Weiss temperature, T W , of about À25 K, indicating that the coupling between magnetic moments of clusters is antiferromagnetic. Possible origins of the ferromagnetism in Rb clusters are discussed.

This paper explores a class of non-linear constitutive relations for materials with memory in the framework of covariant macroscopic Maxwell theory. Based on earlier models for the response of hysteretic ferromagnetic materials to prescribed slowly varying magnetic background fields, generalized models are explored that are applicable to accelerating hysteretic magneto-electric substances coupled selfconsistently to Maxwell fields. Using a parameterized model consistent with experimental data for a particular material that exhibits purely ferroelectric hysteresis when at rest in a slowly varying electric field, a constitutive model is constructed that permits a numerical analysis of its response to a driven harmonic electromagnetic field in a rectangular cavity. This response is then contrasted with its predicted response when set in uniform rotary motion in the cavity.

A new vanadium(III) phosphate, (NH 4)[V(PO 4)F], has been synthesized by using mild hydrothermal conditions under autogeneous pressure. The crystal structure has been solved from X-ray single crystal data. The compound crystallizes in the Pnna orthorhombic space group, with the unit-cell parameters a ¼ 12:982ð2Þ; b ¼ 10:608ð1Þ; c ¼ 6:4789ð6Þ Å and Z ¼ 8: The final R factors were R 1 ¼ 0:077 [all data] and wR 2 ¼ 0:068: The crystal structure consists of a three-dimensional framework formed by VO 4 F 2 octahedra and tetrahedral (PO 4) 3À phosphate anions. The vanadium(III) cations from the VO 4 F 2 octahedra are linked through the fluorine atoms giving rise to zigzag chains. The ammonium cations are located in the cavities of the structure compensating the anionic charge of the [V(PO 4)F] À inorganic skeleton. The IR spectrum shows the characteristic bands of the phosphate anion. The diffuse reflectance spectroscopy allowed us to calculate the Dq and Racah parameters. The values are Dq ¼ 1540; B ¼ 505 and C ¼ 2460 cm À1. Magnetic measurements indicate the existence of weak ferromagnetic interactions.

In this (partly review) paper several important situations are analyzed in which molecular systems are distorted, but there are no apparent degeneracies or close in energy states to justify their origin as due to the Jahn-Teller effect (JTE) or pseudo JTE (PJTE). It is shown that in all these cases above the JTE are ''hidden'' in the excited states of the undistorted configuration even when the energy gap to these states is very large, and the involvement of these states in the vibronic coupling explains the JT origin of the distortions. This confirms the general validity of the JTE as the only source of instabilities and distortions of high-symmetry configurations of polyatomic systems. For the example of the ozone molecule, which has no degenerate ground state, neither in the distorted (obtuse-triangular), nor in the undistorted (regular triangular) configurations, and there are no low-lying excited states, the distortion is shown to emerge from the JTE in the excited E state situated at $8.3 eV above the ground state. The JT stabilization energy is more than $9 eV which makes the distorted configuration the lowest in energy.

Ferromagnetic materials, such as steel, are used for shielding of power and telecommunication cables. These shields often provide path for currents during faults or lightning and are important for the integrity and safety of electrical systems and devices. Since such currents might be with low-or high-frequency content, and of low or high intensity, ferromagnetic shield behavior might be quite different due to hysteresis. This paper describes a method for analyzing the dynamic behavior of ferromagnetic cable shields based on the Jiles model of hysteresis. The solution is implemented in ATP-EMTP, which allows one to analyze the complex behavior of ferromagnetic cable shields in conjunction with that of the other elements of the power system. Due to limitations of the model of hysteresis, application of the proposed model is limited to frequencies up to about 10 kHz. The model is illustrated for a practical 100-m-long cable.

It is the  laboratory agenda of "Electricity and Magnetism Physics" and "Electrical Circuits" in Persian language (Farsi) which includes: Passive Elements (Resistors, Capacitors and Inductors) - AC/DC Sources (Power-Supply, Function Generator and Signal Generator) - Multimeter - Measurement Error - Ohm's Law - Equivalent Resistance - Kirchhoff's Laws - Wheatstone Bridge - Metre Bridge - Oscilloscope - Capacitor Charging and Discharging - The Frequency Response of RC, RL and RLC Circuits - Magnetism - Ferromagnetism - Faraday's Law - Lenz's Law - Transformer - AC/DC Electromotors - AC/DC Generators (Turbines and Dynamo).

See:
http://dx.doi.org/10.13140/RG.2.2.21250.43207/1

and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, redistribution , reselling , loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

In this paper a mathematical model of coupled heat transfer and electromagnetic phenomena in induction heaters of ferromagnetic, steel pipes has been described. The model takes into account the nonlinearity of all coefficients, the characteristics of the supply source, and the thermal influence of the lining. A method of partial decoupling of fields has been proposed. Experimental verification of the computed results has also been presented.

PAPER DFT investigations on mechanical stability, electronic structure and magnetism in Co 2 TaZ (Z = Al, Ga, In) heusler alloys Abstract Ferromagnetic Heusler compounds have vast and imminent applications for novel devices, smart materials thanks to density functional theory (DFT) based simulations, which have scored out a new approach to study these materials. We forecast the structural stability of Co 2 TaZ alloys on the basis of total energy calculations and mechanical stability criteria. The elastic constants, robust spin-polarized ferromagnetism and electron densities in these half-metallic alloys are also discussed. The observed structural aspects calculated to predict the stability and equilibrium lattice parameters agree well with the experimental results. The elastic parameters like elastic constants, bulk, Young's and shear moduli, poison's and Pugh ratios, melting temperatures, etc have been put together to establish their mechanical properties. The elaborated electronic band structures along with indirect band gaps and spin polarization favour the application of these materials in spintronics and memory device technology.

The projection of integrating optical, magnetic and electronic functionalities into a single material have aggravated passionate attention in mounting wide band gap diluted magnetic semiconductor (DMS) in the midst of room temperature ferromagnetism. We report the evidence of ferromagnetism in Cu-doped ZnSe quantum dots (QDs) below room temperature, grown from a single source precursor by lyothermal method with the sizes of approximately 3.2-5.14 nm. QDs mainly exhibit paramagnetic behavior between 80 and 300 K, with a weak ferromagnetic/anti-ferromagnetic exchange at lower temperature as observed by superconducting quantum interference device (SQUID) magnetometer. From the Curie-Weiss behavior of the susceptibility, Curie temperature (T c ) of Cu-doped ZnSe sample has been evaluated. From EPR, we obtain the Lande-g factor in the Zeeman interaction term as 2.060. Photoluminescence and EPR measurements support and confirm the view that Cu 2? substitutes for Zn 2? in Cu-doped ZnSe quantum dots.

We review the first decade of extensive optical studies of ferromagnetic, III-Mn-V diluted magnetic semiconductors. Mn introduces holes and local moments to the III-V host, which can result in carrier mediated ferromagnetism in these disordered semiconductors. Spectroscopic experiments provide direct access to the strength and nature of the exchange between holes and local moments; the degree of itineracy of the carriers; and the evolution of the states at the Fermi energy with doping. Taken together, diversity of optical methods reveal that Mn is an unconventional dopant, in that the metal to insulator transition is governed by the strength of the hybridization between Mn and its p-nictogen neighbor. The interplay between the optical, electronic and magnetic properties of III-Mn-V magnetic semiconductors is of fundamental interest and may enable future spin-optoelectronic devices. arXiv:0810.3669v1 [cond-mat.mtrl-sci]

Nanoparticles samples of pure SnO 2 , Sn 0. were synthesized by sol-gel method. X-ray diffraction analysis and Fourier transform infrared spectra of all prepared samples confirmed the formation of single phase SnO 2 with tetragonal rutile structure. The average crystallite sizes of the prepared samples were estimated to be in the range of 7-12 nm. Energy-dispersive X-ray spectroscopy analysis of Sn 0.98 Mn 0.02 O 2 , Sn 0.96 Mn 0.02 Fe 0.02 O 2 , and Sn 0.96 Mn 0.02 Co 0.02 O 2 samples evidently proved the existence of Mn, Fe, Co, Sn, and O elements only without any impurity, indicating the high purity of the prepared samples. Transmission electron microscopy images showed the formation of ultra-fine spherical nano-particles in all samples with average particles sizes of 8.5-15 nm. From the UV-Vis absorption spectra results, the band gap energy value of the pure SnO 2 nanoparticles was estimated to be 3.90 eV and it varied with dopant type and its concentration. Room temperature magnetic hysteresis loops of all samples exhibited ferromagnetic behavior. Clear enhancement in the room temperature ferromagnetism was achieved in pure SnO 2 nanoparticles after doping with Mn and codoping with (Mn, Fe) or (Mn, Co) dopants. The maximum value of the saturation magnetization was found in Sn 0.96 Mn 0.02 Fe 0.02 O sample, while Sn 0.96 Mn 0.02 Co 0.02 O sample displayed the higher values of coercivity and retentivity. Graphical Abstract

Two bis(oxalato)cuprate(II) hybrid salts, (C5H7N2)2[Cu(C2O4)2 ]·2H2O (1) and (C7H11N 2)2 [Cu(C2O4)2 ]·5H2O (2) (C5H7N2 = 3-aminopyridinium; C7H11N2 = 2-amino-4,6-dimethylpyridinium) have been synthesized and characterized by elemental and thermal analyses, IR and UV-Vis spectroscopies, single-crystal X-ray diffraction, and SQUID magnetometry. The polymeric anionic motifs in the two salts are significantly different. In 1, stacking of [Cu(C2O4)2 ] 2-units through axial Cu···O contacts (2.890 Å) yields straight Cu(II) chains, with a prolate CuO6 octahedron around Cu(II) ions, formed by two cis-chelated oxalate anions and two axial O-atoms of neighboring [Cu(C2O4)2 ] 2-units. By contrast, in 2, stacking of [Cu(C2O4)2 ] 2-units occurs via bis-bidentate oxalate groups, yielding zigzag Cu(II) chains with a distorted CuO6 coordination sphere. Thermal studies confirmed the presence of solvent water molecules in both salts. Magnetic studies revealed weak antiferromagnetic and weak ferromagnetic interactions between Cu(II) ions in 1 and 2, respectively.

Multiferroic BaTiO3–CoFe2O4–BaTiO3thin films were synthesized by spin coating of Co(NO3)2–Fe(NO3)3and Ba(OAc)2–Ti(i-OPr)4dissolved in a mixture of acetic acid and dimethylformamide. Stepwise thermaltreatment at 200, 400 and 800◦C led to the desired phases. The phase formation process was monitoredby thermoanalytic, XRD, IR and Raman measurements. SEM was used to characterize the structure andthickness of each layer. Two samples with different thicknesses of perovskite and spinel layers are dis-cussed. Sample 1 consists of 120 nm CoFe2O4between two 70 nm BaTiO3layers. For sample 2, the 90 nmBaTiO3top and bottom layers are enclosing 220 nm CoFe2O4. The surface qualities were determined byAFM indicating rms roughness values of about 4 nm. Magnetic investigations reveal slightly anisotropicbehavior. Polarization measurements show hysteresis loops (PS(max)= 29 µC cm−2; PR(max)= 17 µC cm−2)with switching peaks at the corresponding coercive fields

The structural, electronic, mechanical and thermodynamic properties of the perovskite oxide BaAmO 3 have been predicted using the full-potential linearized augmented plane wave (FP-LAPW) method. The equilibrium lattice constant, bulk modulus and pressure derivative were computed using different exchange correlations. The optimization of structure was carried out in ferromagnetic, anti-ferromagnetic and non-magnetic states, and the compound was found to be stable in the ferromagnetic state. A systematic study on the band structure and density of states was accomplished using generalized gradient approximation (GGA), Hubbard approximation (GGA+U) and modified Becke-Johnson exchange potential (mBJ),and the compound was found to have a half-metallic nature in all the approximations. The calculated total spin magnetic moment was found to be 5 μ B in all the approximations used. The second-order elastic constants, Young modulus, shear modulus, Poisson ratio and anisotropic factor have Sajad Ahmad Dar also been calculated. In order to have a complete understanding of BaAmO 3 , the thermodynamic properties were studied in the pressure range of 0 to 40 GPa and the temperature range extending from 0 to 600 K.

In this work the Mn 5 Si 3 and Mn 5 SiB 2 phases were produced via arc melting and heat treatment at 1000 1C for 50 h under argon. A detailed microstructure characterization indicated the formation of single-phase Mn 5 Si 3 and near single-phase Mn 5 SiB 2 microstructures. The magnetic behavior of the Mn 5 Si 3 phase was investigated and the results are in agreement with previous data from the literature, which indicates the existence of two anti-ferromagnetic structures for temperatures below 98 K. The Mn 5 SiB 2 phase shows a ferromagnetic behavior presenting a saturation magnetization M s of about 5.35 Â 10 5 A/m (0.67 T) at room temperature and an estimated Curie temperature between 470 and 490 K. In addition, AC susceptibility data indicates no evidence of any other magnetic ordering in 4-300 K temperature range. The magnetization values are smaller than that calculated using the magnetic moment from previous literature NMR results. This result suggests a probable ferrimagnetic arrangement of the Mn moments.

Zn 1Àx Co x O (x = 0, 0.05, and 0.07) nanorods (NRs) exhibiting ferromagnetism above room temperature and with high magnetic moment have been synthesized by a solvothermal route. XRD, FESEM, TEM, EDS and XPS measurements reveal the growth of single phase wurtzite structure Zn 1Àx Co x O NRs with the successful incorporation of Co ions inside the ZnO matrix. TEM micrograph reveals clearly the formation of long ZnO NRs with diameter of 50-90 nm and length of 0.3-0.6 lm. High resolution TEM lattice images and the electron diffraction patterns show that all the NRs are single crystalline. Room temperature magnetic measurements exhibit ferromagnetic behavior with high magnetic moment of 1.83 emu/g for 2 T field, coercivity of 53 G. Temperature dependent magnetization measurement shows a Curie temperature of the order of 398 K. Photoluminescence (PL) spectra exhibit near band edge UV emission and defect related visible emission, which is expected to play a significant role in the FM ordering. PL and UV-VIS spectra reveal slight modification of band edge due to doping effect. Systemic structural, magnetic, and optical studies reveal that both the nature of the defects as well as Co 2+ ions are significant ingredients to attain high moment as well as high ordering temperature in the 1-dimensional ZnO NRs. Magnetic interaction is quantitatively analyzed and explained using a bound magnetic polaron model and expected to arise from the intrinsic exchange interaction of Co ions and V Zn , O i related defects. These findings provides a better insight into the underlying mechanisms of high temperature ferromagnetism in Zn 1Àx Co x O NRs.

A controlled technique for embedding ferromagnetic nanoparticles in a diamagnetic PVC matrix with uniform dispersion and a wide particle concentration range is described here. The resulting material is a magnetopolymeric nanocomposite with combined magnetic and polymeric properties. The tailoring of its magnetic response can be tuned through the control of nearly spherical Co80Ni20 nanoparticles around 65 nm average diameter, prepared by the polyol method, and their concentration in the matrix (in the range 0.5–50 wt%). This material is nearly ready for practical applications.

The two isomeric organic nitronyl nitroxide free radicals 2-(2'-hydroxyl-3'-methoxy-phenyl)-4, 4, 5, 5-tetramethyl-4, 5-dihy- dro-1H-imidazoyl-1-oxyl-3-oxide, 1, and 2-(3'-hydroxyl-4'-methoxy- phenyl)-4, 4, 5, 5-tetramethyl-4, 5-dihydro-1H-imidazoyl-1-oxyl-3- oxide, 2, have been synthesized and their structures determined by X-ray diffraction. Structure 1 has three dimensional, strong, intra- molecular hydrogen bonds in addition to intermolecular interactions favoring sheets. The structure of radical 2 also shows strong hydrogen bonds both intra- and intermolecular. Some of these bonds are with a lattice water molecule, yielding a three-dimensional crystal structure. An important structural difference between both radicals is that in compound 1, one of the nitrogen atoms of the radical shows smaller angles than the other atom in the same radical and than both nitrogen atoms in compound 2. This suggests that in 1, one of the nitrogen atoms has a higher sp 3 character ...

Reaction of a metal imidazolate complex, Mlm (M=Cu" or Nil'), with Cr(TPP)CI or Cr(TPP)C104 affords the dinuclear complexes, Cr(TPP)(Mlm)CI, and the trinuclear complexes, [Cr(TPP)(Mlm)2]C104 (TPP is the dianion of tetraphenylporphyrin), respectively, which exhibit ferromagnetic coupling in the Cr-Cu complexes.

The fabrication of highly-oriented polycrystalline ceramics of Bi 5 Fe 0.5 Co 0.5 Ti 3 O 15 (BFCT), prepared via molten salt synthesis and uniaxial pressing of high aspect ratio platelets is reported. Electron backscatter images show a secondary phase within the ceramic which is rich in cobalt and iron. The concentration of the secondary phase obtained from scanning electron microscopy (SEM) is estimated at less than 2 % by volume, below the detection limit of X-ray diffraction. The samples were characterized by X-ray diffraction, polarization-electric field measurements, superconducting quantum interference device (SQUID) as a function of sample orientation and vibrating sample magnetometry (VSM) as a function of temperature. It is inferred from the data that the observed ferromagnetic response is dominated by the secondary phase. This work highlights the importance of rigorous materials characterisation in the study of multiferroics as small amounts of secondary phase, below the limit of XRD, can lead to false conclusions.

We report the thermal behavior of gadolinium foils to be used in magneto thermoelectric generator cells. Magneto thermoelectric generator cell technology exploits the ferromagnetic phase transition of gadolinium to drive the movement of a diaphragm 'shuttle' whose mechanical energy is converted to electrical form and which enhances heat transfer through both conduction and convection. Efficient heat transfer at mechanical interfaces is critical to increase shuttle speed and the commensurate rate of heat transfer. The synthesis and characterization of carbon nanotube thermal interfaces for the gadolinium foils are described. The total thermal interface resistance of the carbon nanotube coated gadolinium was measured using a one-dimensional reference calorimeter technique. Improvement of carbon nanotube growth based on parametric process variations is described, and the effect of hydrogen embrittlement on the magnetic properties of the gadolinium foils during carbon nanotube growth is quantified. The samples generated in this study were consistently measured with total thermal interface resistances in the range of 65-105 mm 2 K/W, a reduction of 55-70% compared to bare gadolinium (R int % 230 mm 2 K/W). The addition of carbon nanotube arrays did not alter the magnetic properties of the gadolinium foils and only a slight decrease in the magnetic moment of the gadolinium samples (8-13%) was measured after growth.

Ferromagnetic nanoparticles when dispersed in a dielectric ceramic matrix offer a new series of percolation composites with a metal-semiconductor or insulator interface that tailors the functional properties. In this purview, ZrO2 of a high dielectric constant (εr) is stabilized in a cubic (c) polymorph by incorporating CrO2 of strongly ferromagnetic nanoparticles. A selective composition 20CrO2–80ZrO2 is synthesized after heating a polymer precursor with glycerol at 500°C–800°C in air for 2 h. Broadening of X-ray diffraction peaks reveals Cr4+:c-ZrO2 with an average crystallite size 5 nm in the 500°C heated sample and that is grown to 8 nm on increasing the temperature to 800°C. They occur as bundles of thin platelets in electron microscopic images. Both the samples have ferromagnetic hysteresis loops with 794 and 211 Oe of coercivities, respectively. Variations of εr-value and the power loss are studied as a function of frequency f (50 Hz–100 kHz range) on cold-pressed pellets at selective temperatures, in the 30°C–500°C range, in describing the effects of the magnetic species.

The magneto-transport of a superconducting/ferromagnetic hybrid structure, consisting of a superconducting thin film in contact with an array of magnetic nanodots in the so-called 'magnetic vortex state', exhibits interesting properties. For certain magnetic states, the stray magnetic field from the vortex array is intense enough to drive the superconducting film into the normal state. In this fashion, the normal-to-superconducting phase transition can be controlled by the magnetic history. The strong coupling between superconducting and magnetic subsystems allows characteristically ferromagnetic properties, such as hysteresis and remanence, to be dramatically transferred into the transport properties of the superconductor.

We study the dependence of magnetic interactions and Curie temperature in Ni (1+x) MnSb system on the Ni concentration within the framework of the density-functional theory. The calculation of the exchange parameters is based on the super-cell and frozen-magnon approaches. The Curie temperatures, TC , are calculated within the random-phase approximation. In agreement with experiment we obtain decrease of the Curie temperature with increasing Ni content.

We report the structural and ferromagnetic properties of Zn 0.97 À x Cr x Co 0.03 O (x ¼ 0.0, 0.03, 0.06 and 0.09) nanoparticles (NPs) synthesized through citric-gel route. X-ray diffraction (XRD) and selected area electron diffraction (SAED) results show the single phase nature with hexagonal wurtzite structure, and reveal the incorporation of Cr 3 þ and Co 2 þ ions into lattice positions of Zn 2 þ ions in ZnO lattice. The average size of NPs decreases from $ 24 to 9 nm with increasing Cr dopant concentrations (x). Micro-Raman and X-ray photoelectron spectroscopy (XPS) studies show the presence of oxygen vacancies (V O ) defects. The XPS study shows interaction between Cr-Co dopant and transfer of electrons from Cr (3d) state to unfilled (3d) state of Co. The observed ferromagnetism is intrinsic in nature, and not due to any metallic segregation or impurity phase. The oxygen vacancies mediated the dopant ions interaction, and the ferromagnetism can be elucidated by bound magnetic polaron (BMP) mechanism.

We report on the optical and magnetic properties of the magnetic semiconductor Zn(V)O fabricated by implantation of 195 keV 51 V + ions into bulk ZnO:Al grown by a hydrothermal technique. Two sets of the samples, containing N d-N a~1 0 15 cm)3 and 10 18 cm)3 , were implanted to doses of 1 • 10 15 cm)2 , 3 • 10 15 cm)2 , and 1 • 10 16 cm)2. The ion implantation was performed at 573 K. To remove irradiation-induced defects, the samples were annealed in air at 1073 K. Photoluminescence (PL) measurements of Zn(V)O films were carried out at temperatures from 10 K to 300 K. The effects of implantation dose and free carrier concentration on the magnetic properties of Zn(V)O were studied using a superconducting quantum interference device magnetometer. Ferromagnetism has been observed in annealed highly conductive samples implanted to 1 • 10 16 cm)2. The PL studies of ZnO bulk samples implanted with V + have revealed that thermal annealing at 1073 K restores to a large extent the optical quality of the material. A new emission line centered at 3.307 eV has been found in the PL spectrum of the highly conductive samples implanted to the dose of 1 • 10 16 cm)2 , which is most probably due to complexes involving V ions.

The magnetic properties of three hexagonal perovskites-Ca 3 Co 2 O 6 , the 2H-and 12H-BaCoO 3Àd-have been studied by magnetization (M) measurements. In the latter, the isothermal magnetic field driven M(H) curves reveal M jumps for the lowest T(¼ 2 K), which are not observed in the 2H-BaCoO 3 1D compound. The comparison to the M steps found in Ca 3 Co 2 O 6 points towards a different origin in the case of the 12H-BaCoO 3Àd perovskite. This suggests that the pinning of the domain walls in this ferromagnet is made by a narrow distribution of critical fields of the nucleation growth responsible for these very reproducible M jumps. A clear relationship to the 3D structural character of the 12H perovskite is also made.

Co-doped ZnO͑Co x Zn 1−x O͒ is of potential interest for spintronics due to the prediction of room-temperature ferromagnetism. We have grown epitaxial Co x Zn 1−x O films on Al 2 O 3 ͑012͒ substrates by metalorganic chemical vapor deposition using a liquid precursor delivery system. High concentrations of Co͑x ഛ 0.35͒ can be uniformly incorporated into the film without phase segregation. Co is found to be in the +2 oxidation state, independent of x, by both surface-sensitive core-level x-ray photoemission and bulk-sensitive optical absorption spectroscopies. This material can be grown n-type by the deliberate incorporation of oxygen vacancies, but not by inclusion of ϳ1 at. % Al. Semiconducting films remain ferromagnetic up to 350 K. In contrast films without oxygen vacancies are insulating and nonmagnetic, suggesting that exchange interaction is mediated by itinerant carriers. The saturation and remanent magnetization on a per Co basis was very small ͑Ͻ0.1 B /Co͒, even in the best films. The dependence of saturation magnetization, as measured by optical magnetic circular dichroism, on magnetic field and temperature, agrees with the theoretical Brillouin function, demonstrating that the majority of the Co͑II͒ ions behave as magnetically isolated S =3/2 ions.

This paper presents real-time MRI-based control of a ferromagnetic microcapsule for endovascular navigation. The concept was studied for future development of microdevices designed to perform minimally invasive interventions in remote sites accessible through the human cardiovascular system. A system software architecture is presented illustrating the different software modules to allow navigation of a microdevice in blood vessels, namely: (i) vessel path planner, (ii) magnetic gradient steering, (iii) tracking and (iv) closed-loop navigation control. First, the position recognition of the microrobot into the blood vessel is extracted using Frangi vesselness filtering from the pre-operation images. Then, a set of minimal trajectory is predefined, using FMM, to guide the microrobot from the injection point to the tumor area through the anarchic vessel network. Based on the pre-computed path, a GPC is proposed for robust time-multiplexed navigation along a 2D path in presence of pulsative flow. The simulation results suggest the validation of the proposed image processing and control algorithms. A series of disturbances introduced in the presence and absence of closed-loop control affirms the robustness and effectiveness of this predictive control system.

The science of physics is based on theories and models as well as experiments: the former structure relations and simplify reality to a degree such that predictions on physical phenomena can be derived by means of mathematics. The latter allow verification or falsification of these predictions. Computer sciences allow a new access to this relationship, especially well-suited for education: New Technologies provide simulations for the model, virtual instruments for running and evaluating real experiments and mathematical toolkits to solve equations derived from the theory analytically and to compare the outcome of all three methods. We will demonstrate this approach on several examples: Ferromagnetism, thermodynamics and the Harmonic Oszillator. We furthermore give a brief example on an online-tutoring system that makes our setup attractive for self-study outside the university campus.

The 5d electron-based Sr 2−x La x IrO 4 system (0 x 0.2) has been synthesized by a solid-state route. The x = 0 composition is a nonmetallic weak ferromagnet with a Curie temperature at about 240 K. The crystal structure behaviour and magnetic properties exhibited by this Sr 2−x La x IrO 4 system can be explained on the basis of the extended character of the 5d electrons of the Ir cation and its valence states. Rietveld analysis of x-ray powder diffraction on Sr 2 IrO 4 agrees well with previous structural neutron experiments. Furthermore, density functional theory (DFT) calculations predict that I 4 1 /acd represents a more stable crystal structure than K 2 NiF 4 (I 4/mmm). Electrical resistivity and magnetic properties of Sr 2−x La x IrO 4 are strongly dependent on the Ir 3+ content. The Sr 2−x La x IrO 4 magnetic behaviour in the range of 2-240 K can be ascribed to a weak ferromagnet, produced by an array of canted antiferromagnetically ordered Ir 4+ magnetic moments.

Dilute magnetic semiconductors and wide gap oxide semiconductors are appealing materials for magnetooptical devices. From a combinatorial screening approach looking at the solid solubility of transition metals in titanium dioxides and of their magnetic properties, we report on the observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8%. Magnetic microscopy images reveal a magnetic domain structure in the films, indicating the existence of ferromagnetic long-range ordering. The materials remain ferromagnetic above room temperature with a magnetic moment of 0.32 Bohr magnetons per cobalt atom. The film is conductive and exhibits a positive magnetoresistance of 60% at 2 kelvin.

The effect of the host lattice structure on the spectroscopic and magnetic properties of Cr 3+ -doped In 2 O 3 nanocrystals is reported. The influence of the dopant ions on the nanocrystal growth allows for the solution-phase stabilization and separation of doped colloidal In 2 O 3 nanocrystals having different crystal structures − stable cubic phase (bcc-In 2 O 3 ) and metastable rhombohedral (rh-In 2 O 3 ) phase − and comparative study of the electronic structure and magnetic properties of Cr 3+ in both polymorphs. Investigations by a range of complementary spectroscopic techniques, including Raman, X-ray absorption and magnetic circular dichroism spectroscopies, revealed that the change in the In 2 O 3 phase leads to distinctly different electronic structure of Cr 3+ dopants, associated with a different nature of the substitutional doping sites and different electronic structure of the nanocrystal host lattice. Nanocrystalline films prepared from colloidal nanocrystals exhibit ferromagnetism at room temperature, although the average magnetic moment of Cr 3+ in rh-In 2 O 3 is an order of magnitude smaller than that in bcc-In 2 O 3 samples. This difference in magnetization is associated with wider band gap of rh-In 2 O 3 nanocrystals, which prevents effective hybridization of the defect donor band, as a mediator of the Cr 3+ magnetic exchange interactions, and the Cr 3+ 3d states at the Fermi level. The results of this work demonstrate that a change in the defect and electronic structures of the same semiconductor host lattice by nanocrystal phase control in solution allows for tuning of the magnetic properties of diluted magnetic semiconducting oxides.

The microcanonical dynamics of an ensemble of random magnetic dipoles in a needle has been investigated. Due to the presence of a constant of motion in the 1-D case, a "dimensional" phase transition in the quasi one dimensional case has been found separating a paramagnetic chaotic phase from a ferromagnetic regular one. In particular, a simple criterium for the transition has been formulated and an intensive critical parameter found. Numerical simulations support our understanding of this complex phenomenon.

By means of X-and Q-band magnetic-resonance measurements we have investigated the magnetic interactions and derived the magnon gap in the ferromagnetic superconductor RuSr 2 GdCu 2 O 8. Two microwave absorptions are observed: first, a paramagnetic resonance of the Gd 3ϩ ions, and second, appearing below the Curie temperature (T Curie), a ferromagnetic resonance due to the ruthenium lattice. Located between the superconducting CuO 2 planes, the Gd ions serve as intrinsic probes of the internal magnetic fields near the Cu sites. Below T Curie the Gd 3ϩ signal shifts, evidencing the appearance of a homogeneous internal field, H Ru-Gd ϳ600 Oe. We show that H Ru-Gd is due to a Ru-Gd ferromagnetic exchange interaction. The Ru ferromagnetic resonance indicates the existence of a magnon anisotropy gap /␥տ4600 Oe. We estimate the out-of-plane and in-plane anisotropy fields to be, respectively, H z ϳ110 kOe and H x ϳ200 Oe.

At ambient pressure, ordered Au 4 V is metallic and displays ferromagnetism at T C = 45 K. The electrical resistivity has been measured as a function of temperature from 1 K to 300 K and as a function of pressure up to 30 GPa using various high-pressure devices. A kink, which is associated with the reduction of scattering due to the onset of ferromagnetic order, is seen in the electrical resistance as a function of temperature. With applied pressure, this kink is found to broaden and increase in temperature at a rate of approximately 2.7 K / GPa. Above ϳ18 GPa, the broadening of the kink prohibits accurate determination of T C ; however, upon reducing the pressure, no signatures of ferromagnetism were evident in the electrical resistivity. Both energy-dispersive ͑P Յ 61 GPa͒ and angle-dispersive ͑P Յ 27 GPa͒ x-ray diffraction measurements at room temperature show a gradual transition from the body-centered-tetragonal phase of Au 4 V to a disordered face-centered-cubic structure. This transition is irreversible and continuous, and the data have been fit to a Birch-Murnaghan equation of state. In order to investigate the origin of the magnetic interactions in Au 4 V, we have also measured the electrical resistivity of Au 1−x V x alloys and determined their Kondo temperatures T K for x Ͻ 1%. The pressure dependence of T K for x = 0.5% was measured up to 2.8 GPa, for which the Kondo temperature increases at a rate of dT K / dP = 6.5 K / GPa. Using the volume dependence of the exchange interaction between magnetic vanadium ions, we find that the pressure-induced increase of the Curie temperature in Au 4 V can be explained by an increase in the exchange interaction parameter and the number of magnetic nearest neighbors.

Magnetic domain structures in phase-separated manganites were investigated by low-temperature Lorentz electron microscopy, in order to understand some unusual physical properties such as a colossal magnetoresistance (CMR) effect and a metal-to-insulator transition. In particular, we examined a spatial distribution of the charge/orbital-ordered (CO/OO) insulator state and the ferromagnetic (FM) metallic one in phase-separated manganites; Cr-doped Nd 0:5 Ca 0:5 MnO 3 and (La 1Àx Pr x Þ 5=8 Ca 3=8 MnO 3 with x ¼ 0:375, by obtaining both the dark-field images and Lorentz electron microscopic ones. It is found that an unusual coexistence of the CO/OO and FM metallic states below a FM transition temperature in the two compounds. The present experimental results clearly demonstrated the coexisting state of the two distinct ground states in manganites.

A recently proposed band model to describe metallic ferromagnetism is studied at finite temperatures within the mean-field approximation. We discuss in particular the behavior of critical temperature, specific heat, magnetic susceptibility above T"and magnetization below T, assuming a constant density of states. The model overcomes in a simple way the major difhculties of Stoner theory and yields properties that are consistent with a variety of observations in ferromagnetic metals and alloys.