Magnetic Profiles at Engineered Perovskite LSMO Heterointerfaces

Scientific reports, 2017

Understanding and controlling the interfacial magnetic properties of ferromagnetic thin films are crucial for spintronic device applications. However, using conventional magnetometry, it is difficult to detect them separately from the bulk properties. Here, by utilizing tunneling anisotropic magnetoresistance in a single-barrier heterostructure composed of La0.6Sr0.4MnO3 (LSMO)/LaAlO3 (LAO)/Nb-doped SrTiO3 (001), we reveal the presence of a peculiar strong two-fold magnetic anisotropy (MA) along the [110]c direction at the LSMO/LAO interface, which is not observed in bulk LSMO. This MA shows unknown behavior that the easy magnetization axis rotates by 90° at an energy of 0.2 eV below the Fermi level in LSMO. We attribute this phenomenon to the transition between the e g and t 2g bands at the LSMO interface. Our finding and approach to understanding the energy dependence of the MA demonstrate a new possibility of efficient control of the interfacial magnetic properties by controlling...

Journal of Applied Physics, 2005

We report on the growth of thin films and heterostructures of the ferromagnetic-insulating perovskite La 0.1 Bi 0.9 MnO 3 . We show that the La 0.1 Bi 0.9 MnO 3 perovskite grows single phased, epitaxially, and with a single out-of-plane orientation either on SrTiO 3 substrates or onto strained La 2/3 Sr 1/3 MnO 3 and SrRuO 3 ferromagnetic-metallic buffer layers. We discuss the magnetic properties of the La 0.1 Bi 0.9 MnO 3 films and heterostructures in view of their possible potential as magnetoelectric or spin-dependent tunneling devices.

Physical Review B, 2012

We present a first-principles study on the interface between perovskite ferroelectrics (PbTiO 3 ) and conducting magnetic manganites (La 1−x Sr x MnO 3 ). We show that by switching the ferroelectric polarization, additional carriers are accumulated or depleted at the interfacial region of the manganite and that this change in carrier density can modify the magnetic spin configuration of the interfacial Mn, which is consistent with the experimentally observed anomalously large change in the magnetization. We also describe an unexpected purely interfacial phenomenon whereby the ferroelectric polarization of the interfacial region changes the magnetic energetics -a degree of freedom not present in bulk manganites. Theoretically, we show the the ground-state magnetic structure depends sensitively on the precise choice of Hubbard U parameter within the widelyused DFT+U class of exchange correlation functionals. We provide a simple Ising-like model that explains the evolution of the magnetic structure with U in tandem with a discussion of various different ways in which one might try to choose an appropriate U parameter. decade [1, 2]. The coexistence of more than one order parameter in a single phase and their coupling may open new routes to the next generation of electronic devices. For instance, the possibility of controlling magnetization via external electric fields may find promising applications in spintronics. The origin of magnetoelectric multiferroicity lies in a nonzero magnetoelectric coupling which may occur due to many different mechanisms (for recent reviews, see [3, 4]). The magnetic properties of an intrinsic bulk magnetoelectric, of which Cr 2 O 3 is a prototype, can be modulated by an external field through the change of the magnetic cations' displacement relative to anions [5]. Extrinsic magnetoelectric couplings are typically mediated by strain: in composites of piezomagnetic materials combined with electrostrictive materials, external fields modulate the electric polarization, as well as the shape of the piezoelectric. This change in turn induces strain of the magnetic components and modifies the magnetization in the magnetostrictive material [6]. However, although these bulk mechanisms are well understood, the magnitude of magnetoelectric couplings in bulk materials is generally small [7], impeding their applications in electronic devices. Moving away from bulk materials, artificial heterostructures such as interfaces are promising candidates for realizing or even engineering magnetoelectric couplings. Recently, a variety of mechanisms were proposed to induce magnetoelectric coupling at interfaces. At ferromagnet/ferroelectric interfaces, the interfacial bond length can be altered by the presence of ferroelectric polarization, for example in Fe/BaTiO 3 [8], Co 2 MnSi/BaTiO 3 [9] and Fe 3 O 4 /BaTiO 3 [10]

Advanced Materials Interfaces, 2015

Correlated oxide materials attract significant attention as the interplay between their charge, spin, orbital and lattice degrees of freedom gives rise to a wide variety of functional properties. This research field is even further enriched by the controlled formation of highly ordered oxide heterostructures in which new functionalities emerge at the interfaces. [1,2] Usually reduced physical properties in ultrathin correlated oxide films are macroscopically measured and attributed to the interfaces, which is referred to as 'dead-layers'. These have been observed in perovskite-type transition-metal oxide heterostructures, such as reduced dielectric (SrTiO 3), [3] ferroelectric (BaTiO 3 and PbTiO 3) [4] and ferromagnetic (SrRuO 3 and La 0.67 Sr 0.33 MnO 3) [5,6] properties. The presence of these dead-layers results in reduced performance of devices due to the local changes in material properties at the interfaces. In perovskite-type transition-metal oxides the interfacial properties depend strongly on the precise atomic stacking sequence at the interface, e.g. the termination dependent conducting or insulating behavior of the LaAlO 3 /SrTiO 3 and LaVO 3 /SrTiO 3 interfaces [7-9] and the

Ferromagnetic/metallic manganese perovskites, such as La2/3Sr1/3MnO3 (LSMO)are promising materials for the design and implementation of novel spintronic devices working at room temperature. However, their implementation in practical applications has been severely hampered due to the breakdown of their magnetotransport properties at temperatures well below their magnetic transition temperature. This breakdown has been usually associated to surface and interface related problems but its physical origin has not been clearly established yet. In this work we investigate the interface between La2/3Sr1/3MnO3 (LSMO) thin films and different capping layers by means of x-ray linear dichroism and transport measurements. Our data reveal that, irrespective to the capping material, LSMO/capping layer bilayers exhibit an antiferromegnetic/insulating phase at the interface, likely to originate from a preferential occupancy of Mn 3d 3z2-r2 eg orbitals. This phase, which extends ca. 2 unit cells, is ...

ACS Applied Materials & Interfaces, 2022

Magnetic insulators with strong perpendicular magnetic anisotropy (PMA) play a key role in exploring pure spin current phenomena and developing ultralowdissipation spintronic devices, thereby it is highly desirable to develop new material platforms. Here we report epitaxial growth of La2/3Sr1/3MnO3 (LSMO)-SrIrO3 (SIO) composite oxide films (LSMIO) with different crystalline orientations fabricated by sequential two-target ablation process using pulsed laser deposition. The LSMIO films exhibit high crystalline quality with homogeneous mixture of LSMO and SIO at atomic level. Ferrimagnetic and insulating transport characteristics are observed, with the temperature-dependent electric resistivity well fitted by Mott variable-range-hopping model. Moreover, the LSMIO films show strong PMA. Through further constructing all perovskite oxide heterostructures of the ferrimagnetic insulator LSMIO and a strong spin-orbital coupled SIO layer, pronounced spin Hall magnetoresistance (SMR) and spin Hall-like anomalous Hall effect (SH-AHE) were observed. These results illustrate the potential application of the ferrimagnetic insulator LSMIO in developing all-oxide ultralow-dissipation spintronic devices.

Physical Review Letters, 2013

Possible ferromagnetism induced in otherwise non-magnetic materials has been motivating intense research in complex oxide heterostructures. Here we show that a confined magnetism is realized at the interface between SrTiO3 and two insulating polar oxides, BiMnO3 and LaAlO3 . By using polarization dependent x-ray absorption spectroscopy, we find that in both cases the magnetism can be stabilized by a negative exchange interaction between the electrons transferred to the interface and local magnetic moments. These local magnetic moments are associated to magnetic Ti 3+ ions at the interface itself for LaAlO3 /SrTiO3 and to Mn 3+ ions in the overlayer for BiMnO3 /SrTiO3 . In LaAlO3 /SrTiO3 the induced magnetism is quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon. 75.47.Lx, 78.70.Dm The progress in oxide thin film technology is opening the possibility of electronic applications based on the peculiar physical properties of oxide interfaces [1, 2]. The best known example is the junction between two nonmagnetic band insulators, LaAlO 3 (LAO) and SrTiO 3 (STO), which hosts a quasi-two-dimensional electron gas (q2DEG) . The functional properties of LAO/STO heterostructures are indeed extraordinary, such as the possibility of driving an insulating to metal transition by electric field gating at room temperature . At the same time, the real ground state properties of this system are still hotly debated due to apparently conflicting observations of ferromagnetic ordering in some samples , and of superconductivity of the q2DEG below 0.3 K [6] in other samples. More recent studies [7-10] have suggested the coexistence of magnetism and superconductivity, quite intriguing for fundamental physics. However, the mere existence and the real nature of this magnetism in LAO/STO are still questioned and urge clarification.

Scientific Reports, 2020

a strong semi-metallic ferromagnet having robust spin polarization and magnetic transition temperature (T c) well above 300 K, has attracted significant attention as a possible candidate for a wide range of memory, spintronic, and multifunctional devices. Since varying the oxygen partial pressure during growth is likely to change the structural and other physical functionalities of La 0.7 Sr 0.3 MnO 3 (LSMO) films, here we report detailed investigations on structure, along with magnetic behavior of LSMO films with same thickness (~30 nm) but synthesized at various oxygen partial pressures: 10, 30, 50, 100, 150, 200 and 250 mTorr. The observation of only (00 l) reflections without any secondary peaks in the XRD patterns confirms the high-quality synthesis of the above-mentioned films. Surface morphology of the films reveals that these films are very smooth with low roughness, the thin films synthesized at 150 mTorr having the lowest average roughness. The increasing of magnetic T c and sharpness of the magnetic phase transitions with increasing oxygen growth pressure suggests that by decreasing the oxygen growth pressure leads to oxygen deficiencies in grown films which induce oxygen inhomogeneity. Thin films grown at 150 mTorr exhibits the highest magnetization with T C = 340 K as these thin films possess the lowest roughness and might exhibit lowest oxygen vacancies and defects. Interpretation and significance of these results in the 30 nm LSMO thin films prepared at different oxygen growth pressures are also presented, along with the existence and growth pressure dependence of negative remanent magnetization (NRM) of the above-mentioned thin films. The miniaturization of devices to increase speed and reduce the cost of materials is an ongoing need for many current and potential magnetic technologies such as spintronics, highly dense non-volatile memory, spin-caloritronics, and different multifunctional micro and nanoscale devices 1-5. Among important materials for device applications are room temperature ferromagnetic oxides such as the manganites, La 1−x Sr x MnO 3 , since their properties can be tuned using a number of degrees of freedom including charge, spin, orbital, and magnetic ordering phenomena 6,7. They are also excellent candidates for novel engineered nanostructures as they exhibit colossal magnetoresistance (CMR) effect which has been used for different multifunctional applications 8-10. La 1− x Sr x MnO 3 also shows CMR phenomena under smaller external magnetic fields compared to the other manganites and strongly correlated materials 11,12. Among the La 1−x Sr x MnO 3 manganites, the optimized stoichiometry La 0.7 Sr 0.3 MnO 3 (LSMO) is one of the most prominent members with outstanding magnetic and magneto-transport properties. Compared to other typical magnetic oxides, LSMO exhibits semi-metallic behavior, outstanding ferromagnetism, high Fermi-level spin polarization, with a bulk magnetic ordering temperature, T C (= 370 K) well above room temperature 13,14. Also, the spin polarization of LSMO can be enhanced up to ~95 %, with a magnetoresistance (MR) proportion of greater than ~1800 % has been achieved ~4 K 15. In addition, LSMO films have been widely utilized in giant tunneling MR in magnetic oxide tunnel junction-based devices with effective spin injection behavior in spin

Advanced Materials Interfaces, 2016

magnetic, orbital, and structural degrees of freedom to deliver exotic magnetic and electronic phases that coexist. Desirable tunable properties, such as colossal magnetoresistance and half-metallicity of La 1x Sr x MnO 3 , a prototype of the family of Re 1x A x MnO 3 , are promising for multifunctional devices, such as solid oxide fuel cells, all-oxide spin FETs, magnetic tunnel junctions, and multiferroic memory. [ 10-12 ] However, oxygen vacancies will be readily induced in perovskite oxide thin fi lms during deposition and will play a crucial role on regulating the electronic and magnetic properties of perovskite oxide thin fi lms. [ 13 ] The effects of the oxygen vacancies on the properties of the oxide fi lms have two aspects. On one hand, oxygen vacancies can bring out novel phenomena and various possibilities for multifunctional device applications, [ 14-17 ] in which oxygen vacancies can move through the fi lms and modify the structural properties around them. The effects of the oxygen vacancies have not been clear yet. On the other hand, oxygen vacancies induce the degraded ferromagnetism and transport properties in mixed-valence manganite fi lms. [ 18-23 ] Full spin polarization and half-metallicity, which are required to reach high spin injection effi ciency in spintronic devices, are damaged in oxygen defi cient fi lms. In these