The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze of... more The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze off-specular neutron scattering from islands on the surface of deuterated polystyrene–polybutylmethacrylate (dPS–PBMA) copolymer film. It is shown that the scattering intensity distribution measured over a broad range of angles of incidence, including the range of total reflection, can be well interpreted within the simple model of random
Off–specular neutron scattering is employed to study islands formation on the surface of deuterat... more Off–specular neutron scattering is employed to study islands formation on the surface of deuterated polystyrene–polybutylmethacrylate (PS–PBMA) copolymer film. It is shown, that the intensity distribution measured over a broad range of angles of incidence and scattering is well described by the distorted wave born approximation (DWBA)-based theory valid either in the kinematic regime or in the range of the total reflection. A set of island parameters such as mean lateral size, concentration, as well as those characterizing their internal structure is found.
... are presented. We used symmetric polystryreneblockpolymethylmethacrylate (deuterated) P(Sb... more ... are presented. We used symmetric polystryreneblockpolymethylmethacrylate (deuterated) P(SbMMAd) lamellar thin films as a self-assembling matrix for the lamellar arrangement of Fe 3 O 4 nanoparticles. Pure copolymer ...
Direct evidence of the nonuniformly canted state of the spin-flop phase induced by a magnetic fie... more Direct evidence of the nonuniformly canted state of the spin-flop phase induced by a magnetic field applied to Fe=Cr100 superlattices is obtained by polarized neutron reflectometry. It is unambiguously demonstrated that the magnetization of the alternating Fe layers is twisted through the multilayer stack proving a stable noncollinear configuration. The maximal tilt at the end layers progressively reduces towards the center of the multilayer. The set of tilt angles is deduced from a model-free data evaluation employing the supermatrix routine. Spin-flip off-specular scattering is determined by the in-plane magnetization fluctuations and is fitted by a theoretical model of domains.
The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze o!... more The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze o!-specular neutron scattering from islands on the surface of deuterated polystyrene}polybutylmethacrylate (dPS}PBMA) copolymer "lm. It is shown that the scattering intensity distribution measured over a broad range of angles of incidence, including the range of total re#ection, can be well interpreted within the simple model of random island distribution over the surface. Only a few "lm and island parameters, such as mean lateral size, concentration, and those characterizing their internal structure are needed to describe a variety of the features observed experimentally.
Neutron reflection was used for the study of the composite films made of symmetric (d-PS-PBMA) di... more Neutron reflection was used for the study of the composite films made of symmetric (d-PS-PBMA) diblock copolymer (molecular weight Mw = 170 and 135 K) with nanoparticles of γ-Fe2O3 (4 and 6 nm in diameter) incorporated in the deuterated PS-domains with different concentrations. From the neutron reflection experiment we determined the period of the lamellar structure and the position of the nanoparticles in the PS-layers. It is important to examine the effect of the particle size on the lamellar structure. We determined that the small nanoparticles (4 nm) concentrate close to d-PS-PBMA interfaces while larger nanoparticles (6 nm) localize in the center of PS domains. This effect is of considerable interest in the elaboration of new composite materials since it will give a control on the particle distribution inside the host domains.
Additional information about the magnetization distribution in magnetic films is obtained with a ... more Additional information about the magnetization distribution in magnetic films is obtained with a 3D-polarimetry set-up. A pilot experiment was performed with the neutron polarization aligned perpendicular to the surface of a Fe-film in a magnetic field parallel to its surface. The Larmorprecession in the magnetic field between two current sheets was used to adjust the neutron polarization perpendicular to the sample surface. This new polarization-magnetization configuration was probed with a Fe-film in specular and off-specular scattering. The off-specular scattering is created by the magnetic domain structure of the Fe-film in remanence. The results of specular and off-specular scattering are reproduced by calculations for the configuration of the incoming neutron polarization parallel to the sample surface and the magnetic field and for the configuration of the incoming neutron polarization perpendicular to the sample surface and the magnetic field.
ABSTRACT Complex oxide materials exhibit a wide variety of fascinating electromagnetic properties... more ABSTRACT Complex oxide materials exhibit a wide variety of fascinating electromagnetic properties related to the coexistence of multiple electronic and magnetic phases.[1,2] The temperature-magnetic field phase diagram of La0.27Pr0.40Ca0.33MnO3 (LPCMO) is intriguing; a ferromagnetic metallic (FMM) phase, charge ordered insulating (COI) phase and conditions where both phases coexist are accessible with changes in temperature and magnetic field.[3] We have performed neutron reflectometry to understand the emergence of the FMM phase in a COI matrix of a LPCMO thin film as functions of temperature, irradiation with light, magnetic field and stress. Specular reflectivity reveals the emergence of ferromagnetism below the phase transition temperature. Diffuse scattering shows that the length scale of FM domains is 1-2 microns. [1] Ch. Renner et al., Nature 416, 518 (2002). [2] L. Zhang et al., Science 298, 805 (2002). [3] T. Dhakal et al., Phys. Rev. B 75, 092404 (2007).
ABSTRACT Organic carbon (OC) stabilization in soils plays a significant role in the global C cycl... more ABSTRACT Organic carbon (OC) stabilization in soils plays a significant role in the global C cycle, therefore the understanding of the structure and function of the OC-soil mineral interface is of high importance. To study the internal structure, films with different combination of simple OC compounds, natural organic matter (NOM), Bi-layers of SA (Stearic Acid) on Glucose and NOM/Hydrophilic-NOM/Hydrophobic-NOM were deposited onto sapphire using spin coating. The phobic and phylic fractions of the NOM are operationally separated by exchange resins. We obtained detailed structural depth profile of the films using the depth-sensitive technique of the neutron reflectometry. The neutron reflectivity data were collected at the MAGICS Reflectometer at Spallation Neutron Source at the ORNL. Self-assembled ordering of SA in a repeating bi-layer structure was observed when it was deposited on NOM, phylic-NOM and Glucose. However, when SA was added to phobic-NOM no ordering of SA was detected. The formation of distinct, immiscible layers is due to insolubility of SA with NOM/Hydrophilic-NOM and Glucose. Our results reveal that the OC-mineral interface form complex layering and that the sequence of the layering depends on the compounds.
Additional information about the magnetization distribution in magnetic films is obtained with a ... more Additional information about the magnetization distribution in magnetic films is obtained with a 3D-polarimetry set-up. A pilot experiment was performed with the neutron polarization aligned perpendicular to the surface of a Fe-film in a magnetic field parallel to its surface. The Larmorprecession in the magnetic field between two current sheets was used to adjust the neutron polarization perpendicular to the sample surface. This new polarization-magnetization configuration was probed with a Fe-film in specular and off-specular scattering. The off-specular scattering is created by the magnetic domain structure of the Fe-film in remanence. The results of specular and off-specular scattering are reproduced by calculations for the configuration of the incoming neutron polarization parallel to the sample surface and the magnetic field and for the configuration of the incoming neutron polarization perpendicular to the sample surface and the magnetic field.
We report the spin structure of an exchange-biased ferromagnetic oxide heterostructure, La(0.67)S... more We report the spin structure of an exchange-biased ferromagnetic oxide heterostructure, La(0.67)Sr(0.33)MnO(3)/SrRuO(3), through magnetization and polarized neutron reflectometry measurements. We reveal that the magnetization reversal process of the La(0.67)Sr(0.33)MnO(3) biased layer critically depends on the frozen-in spin structure of the SrRuO(3) biasing layer during the cooling process. Furthermore, we observe unexpected double-shifted hysteresis loops of the biased layer that originates from the formation of lateral 180° magnetic domains within the biasing layer, a new mechanism not found in conventional exchange-bias systems.
Oxygen vacancy distributions and dynamics directly control the operation of solid-oxide fuel cell... more Oxygen vacancy distributions and dynamics directly control the operation of solid-oxide fuel cells and are intrinsically coupled with magnetic, electronic and transport properties of oxides. For understanding the atomistic mechanisms involved during operation of the cell it is highly desirable to know the distribution of vacancies on the unit-cell scale. Here, we develop an approach for direct mapping of oxygen vacancy concentrations based on local lattice parameter measurements by scanning transmission electron microscopy. The concept of chemical expansivity is demonstrated to be applicable on the subunit-cell level: local stoichiometry variations produce local lattice expansion that can be quantified. This approach was successfully applied to lanthanum strontium cobaltite thin films epitaxially grown on substrates of different symmetry, where polarized neutron reflectometry revealed a strong difference in magnetic properties. The different vacancy content found in the two films suggests the change in oxygen chemical potential as a source of distinct magnetic properties, opening pathways for structural tuning of the vacancy concentrations and their gradients.
The availability of high-power spallation neutron sources, along with advances in the development... more The availability of high-power spallation neutron sources, along with advances in the development of coupled moderators and neutron polarizers, has made it possible to use polarized neutrons on time-of-flight diffractometers for in situ studies of phenomena contributing to field-induced magnetization of a material. Different electronic and structural phenomena that contribute to the overall magnetization of a material can be studied and clearly identified with polarized neutron diffraction measurements. This article reports the first results from polarized neutron diffraction experiments on a time-of-flight instrument at a spallation source. Magnetic field-induced rotation of electron spins in an Ni-Mn-Ga single crystal was measured with polarized neutron diffraction at the MAGICS reflectometer at the Spallation Neutron Source at Oak Ridge National Laboratory. The difference in intensities measured with spin-up and spin-down polarized neutrons is proportional to the field-induced magnetization of the crystal. The polarized neutron measurements indicate that the magnetic form factor for the 3d electrons of Mn in Ni-Mn-Ga is lower than the value reported earlier for an ideal spherical symmetry of electronic distribution. Future experiments for studying field-induced magnetization in materials following the current methodology are outlined.
The complexity of the mineral−organic carbon interface may 15 influence the extent of stabilizati... more The complexity of the mineral−organic carbon interface may 15 influence the extent of stabilization of organic carbon compounds in soils, which 16 is important for global climate futures. The nanoscale structure of a model interface 17 was examined here by depositing films of organic carbon compounds of contrasting 18 chemical character, hydrophilic glucose and amphiphilic stearic acid, onto a soil 19 mineral analogue (Al 2 O 3 ). Neutron reflectometry, a technique which provides depth-20 sensitive insight into the organization of the thin films, indicates that glucose 21 molecules reside in a layer between Al 2 O 3 and stearic acid, a result that was verified 22
ABSTRACT The development of ``spintronics'' devices based on charge and spin tran... more ABSTRACT The development of ``spintronics'' devices based on charge and spin transport has signaled a paradigm shift in the design of data storage and computing technologies. Magnetoelectric materials, which exhibit intrinsic coupling between electronic and magnetic order, are ideal for these applications. Unfortunately, single-phase magnetoelectrics are exceedingly rare in nature and attention has turned to composite heterostructures that display coupled functionalities at interfaces. A promising system in which to explore this coupling is a thin film oxide heterostructure of the piezoelectric Pb(Zr0.2Ti0.8)O3 (PZT) and the half-metal La0.7Sr0.3MnO3 (LSMO). We show that it is possible to construct a capacitor-type device structure from these materials that may form the basis for an electrically-switched magnetic memory. We conduct polarized neutron reflectometry (PNR) measurements and measure changes in the magnetization depth profile throughout the composite under the reversal of an in situ electric field. We then correlate these PNR results to local strain and chemistry using transmission electron microscopy (TEM). We find that a combination of charge doping and strain mechanisms governs coupling in this system.
ABSTRACT Early GMR devices relied on antiferromagnetic interlayer coupling to work and it was sho... more ABSTRACT Early GMR devices relied on antiferromagnetic interlayer coupling to work and it was shown that the interlayer coupling is in fact oscillatory, with both ferromagnetic and antiferromagnetic interlayer exchange depending on the thickness of the nonmagnetic layer [1,2]. Different competing interactions such as magnetic anisotropy and interlayer afm coupling occur in multilayer systems. Distinguishing the individual contributions is one of the major challenges in the study of multilayered systems. We used polarized neutron reflectivity with full polarization analysis to understand how the magnetization is distributed through the system and how deep the flipping process of the magnetization goes into the system. The easy axis field dependence of occurrence of spin-flop and spin-flip events in the system will be reported. [4pt] [1] S. S. P. Parkin, Phys. Rev. Lett. 71, 1641 (1993).[0pt] [2] D. Elefant, et al., Phys. Rev. B 77, 014426 (2008).
The voltage sensor domain (VSD) of voltage-gated cation (e.g., Na(+), K(+)) channels central to n... more The voltage sensor domain (VSD) of voltage-gated cation (e.g., Na(+), K(+)) channels central to neurological signal transmission can function as a distinct module. When linked to an otherwise voltage-insensitive, ion-selective membrane pore, the VSD imparts voltage sensitivity to the channel. Proteins homologous with the VSD have recently been found to function themselves as voltage-gated proton channels or to impart voltage sensitivity to enzymes. Determining the conformational changes associated with voltage gating in the VSD itself in the absence of a pore domain thereby gains importance. We report the direct measurement of changes in the scattering-length density (SLD) profile of the VSD protein, vectorially oriented within a reconstituted phospholipid bilayer membrane, as a function of the transmembrane electric potential by time-resolved X-ray and neutron interferometry. The changes in the experimental SLD profiles for both polarizing and depolarizing potentials with respect to zero potential were found to extend over the entire length of the isolated VSD's profile structure. The characteristics of the changes observed were in qualitative agreement with molecular dynamics simulations of a related membrane system, suggesting an initial interpretation of these changes in terms of the VSD's atomic-level 3-D structure.
The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze of... more The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze off-specular neutron scattering from islands on the surface of deuterated polystyrene–polybutylmethacrylate (dPS–PBMA) copolymer film. It is shown that the scattering intensity distribution measured over a broad range of angles of incidence, including the range of total reflection, can be well interpreted within the simple model of random
Off–specular neutron scattering is employed to study islands formation on the surface of deuterat... more Off–specular neutron scattering is employed to study islands formation on the surface of deuterated polystyrene–polybutylmethacrylate (PS–PBMA) copolymer film. It is shown, that the intensity distribution measured over a broad range of angles of incidence and scattering is well described by the distorted wave born approximation (DWBA)-based theory valid either in the kinematic regime or in the range of the total reflection. A set of island parameters such as mean lateral size, concentration, as well as those characterizing their internal structure is found.
... are presented. We used symmetric polystryreneblockpolymethylmethacrylate (deuterated) P(Sb... more ... are presented. We used symmetric polystryreneblockpolymethylmethacrylate (deuterated) P(SbMMAd) lamellar thin films as a self-assembling matrix for the lamellar arrangement of Fe 3 O 4 nanoparticles. Pure copolymer ...
Direct evidence of the nonuniformly canted state of the spin-flop phase induced by a magnetic fie... more Direct evidence of the nonuniformly canted state of the spin-flop phase induced by a magnetic field applied to Fe=Cr100 superlattices is obtained by polarized neutron reflectometry. It is unambiguously demonstrated that the magnetization of the alternating Fe layers is twisted through the multilayer stack proving a stable noncollinear configuration. The maximal tilt at the end layers progressively reduces towards the center of the multilayer. The set of tilt angles is deduced from a model-free data evaluation employing the supermatrix routine. Spin-flip off-specular scattering is determined by the in-plane magnetization fluctuations and is fitted by a theoretical model of domains.
The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze o!... more The distorted wave born approximation (DWBA)-based theory is developed and employed to analyze o!-specular neutron scattering from islands on the surface of deuterated polystyrene}polybutylmethacrylate (dPS}PBMA) copolymer "lm. It is shown that the scattering intensity distribution measured over a broad range of angles of incidence, including the range of total re#ection, can be well interpreted within the simple model of random island distribution over the surface. Only a few "lm and island parameters, such as mean lateral size, concentration, and those characterizing their internal structure are needed to describe a variety of the features observed experimentally.
Neutron reflection was used for the study of the composite films made of symmetric (d-PS-PBMA) di... more Neutron reflection was used for the study of the composite films made of symmetric (d-PS-PBMA) diblock copolymer (molecular weight Mw = 170 and 135 K) with nanoparticles of γ-Fe2O3 (4 and 6 nm in diameter) incorporated in the deuterated PS-domains with different concentrations. From the neutron reflection experiment we determined the period of the lamellar structure and the position of the nanoparticles in the PS-layers. It is important to examine the effect of the particle size on the lamellar structure. We determined that the small nanoparticles (4 nm) concentrate close to d-PS-PBMA interfaces while larger nanoparticles (6 nm) localize in the center of PS domains. This effect is of considerable interest in the elaboration of new composite materials since it will give a control on the particle distribution inside the host domains.
Additional information about the magnetization distribution in magnetic films is obtained with a ... more Additional information about the magnetization distribution in magnetic films is obtained with a 3D-polarimetry set-up. A pilot experiment was performed with the neutron polarization aligned perpendicular to the surface of a Fe-film in a magnetic field parallel to its surface. The Larmorprecession in the magnetic field between two current sheets was used to adjust the neutron polarization perpendicular to the sample surface. This new polarization-magnetization configuration was probed with a Fe-film in specular and off-specular scattering. The off-specular scattering is created by the magnetic domain structure of the Fe-film in remanence. The results of specular and off-specular scattering are reproduced by calculations for the configuration of the incoming neutron polarization parallel to the sample surface and the magnetic field and for the configuration of the incoming neutron polarization perpendicular to the sample surface and the magnetic field.
ABSTRACT Complex oxide materials exhibit a wide variety of fascinating electromagnetic properties... more ABSTRACT Complex oxide materials exhibit a wide variety of fascinating electromagnetic properties related to the coexistence of multiple electronic and magnetic phases.[1,2] The temperature-magnetic field phase diagram of La0.27Pr0.40Ca0.33MnO3 (LPCMO) is intriguing; a ferromagnetic metallic (FMM) phase, charge ordered insulating (COI) phase and conditions where both phases coexist are accessible with changes in temperature and magnetic field.[3] We have performed neutron reflectometry to understand the emergence of the FMM phase in a COI matrix of a LPCMO thin film as functions of temperature, irradiation with light, magnetic field and stress. Specular reflectivity reveals the emergence of ferromagnetism below the phase transition temperature. Diffuse scattering shows that the length scale of FM domains is 1-2 microns. [1] Ch. Renner et al., Nature 416, 518 (2002). [2] L. Zhang et al., Science 298, 805 (2002). [3] T. Dhakal et al., Phys. Rev. B 75, 092404 (2007).
ABSTRACT Organic carbon (OC) stabilization in soils plays a significant role in the global C cycl... more ABSTRACT Organic carbon (OC) stabilization in soils plays a significant role in the global C cycle, therefore the understanding of the structure and function of the OC-soil mineral interface is of high importance. To study the internal structure, films with different combination of simple OC compounds, natural organic matter (NOM), Bi-layers of SA (Stearic Acid) on Glucose and NOM/Hydrophilic-NOM/Hydrophobic-NOM were deposited onto sapphire using spin coating. The phobic and phylic fractions of the NOM are operationally separated by exchange resins. We obtained detailed structural depth profile of the films using the depth-sensitive technique of the neutron reflectometry. The neutron reflectivity data were collected at the MAGICS Reflectometer at Spallation Neutron Source at the ORNL. Self-assembled ordering of SA in a repeating bi-layer structure was observed when it was deposited on NOM, phylic-NOM and Glucose. However, when SA was added to phobic-NOM no ordering of SA was detected. The formation of distinct, immiscible layers is due to insolubility of SA with NOM/Hydrophilic-NOM and Glucose. Our results reveal that the OC-mineral interface form complex layering and that the sequence of the layering depends on the compounds.
Additional information about the magnetization distribution in magnetic films is obtained with a ... more Additional information about the magnetization distribution in magnetic films is obtained with a 3D-polarimetry set-up. A pilot experiment was performed with the neutron polarization aligned perpendicular to the surface of a Fe-film in a magnetic field parallel to its surface. The Larmorprecession in the magnetic field between two current sheets was used to adjust the neutron polarization perpendicular to the sample surface. This new polarization-magnetization configuration was probed with a Fe-film in specular and off-specular scattering. The off-specular scattering is created by the magnetic domain structure of the Fe-film in remanence. The results of specular and off-specular scattering are reproduced by calculations for the configuration of the incoming neutron polarization parallel to the sample surface and the magnetic field and for the configuration of the incoming neutron polarization perpendicular to the sample surface and the magnetic field.
We report the spin structure of an exchange-biased ferromagnetic oxide heterostructure, La(0.67)S... more We report the spin structure of an exchange-biased ferromagnetic oxide heterostructure, La(0.67)Sr(0.33)MnO(3)/SrRuO(3), through magnetization and polarized neutron reflectometry measurements. We reveal that the magnetization reversal process of the La(0.67)Sr(0.33)MnO(3) biased layer critically depends on the frozen-in spin structure of the SrRuO(3) biasing layer during the cooling process. Furthermore, we observe unexpected double-shifted hysteresis loops of the biased layer that originates from the formation of lateral 180° magnetic domains within the biasing layer, a new mechanism not found in conventional exchange-bias systems.
Oxygen vacancy distributions and dynamics directly control the operation of solid-oxide fuel cell... more Oxygen vacancy distributions and dynamics directly control the operation of solid-oxide fuel cells and are intrinsically coupled with magnetic, electronic and transport properties of oxides. For understanding the atomistic mechanisms involved during operation of the cell it is highly desirable to know the distribution of vacancies on the unit-cell scale. Here, we develop an approach for direct mapping of oxygen vacancy concentrations based on local lattice parameter measurements by scanning transmission electron microscopy. The concept of chemical expansivity is demonstrated to be applicable on the subunit-cell level: local stoichiometry variations produce local lattice expansion that can be quantified. This approach was successfully applied to lanthanum strontium cobaltite thin films epitaxially grown on substrates of different symmetry, where polarized neutron reflectometry revealed a strong difference in magnetic properties. The different vacancy content found in the two films suggests the change in oxygen chemical potential as a source of distinct magnetic properties, opening pathways for structural tuning of the vacancy concentrations and their gradients.
The availability of high-power spallation neutron sources, along with advances in the development... more The availability of high-power spallation neutron sources, along with advances in the development of coupled moderators and neutron polarizers, has made it possible to use polarized neutrons on time-of-flight diffractometers for in situ studies of phenomena contributing to field-induced magnetization of a material. Different electronic and structural phenomena that contribute to the overall magnetization of a material can be studied and clearly identified with polarized neutron diffraction measurements. This article reports the first results from polarized neutron diffraction experiments on a time-of-flight instrument at a spallation source. Magnetic field-induced rotation of electron spins in an Ni-Mn-Ga single crystal was measured with polarized neutron diffraction at the MAGICS reflectometer at the Spallation Neutron Source at Oak Ridge National Laboratory. The difference in intensities measured with spin-up and spin-down polarized neutrons is proportional to the field-induced magnetization of the crystal. The polarized neutron measurements indicate that the magnetic form factor for the 3d electrons of Mn in Ni-Mn-Ga is lower than the value reported earlier for an ideal spherical symmetry of electronic distribution. Future experiments for studying field-induced magnetization in materials following the current methodology are outlined.
The complexity of the mineral−organic carbon interface may 15 influence the extent of stabilizati... more The complexity of the mineral−organic carbon interface may 15 influence the extent of stabilization of organic carbon compounds in soils, which 16 is important for global climate futures. The nanoscale structure of a model interface 17 was examined here by depositing films of organic carbon compounds of contrasting 18 chemical character, hydrophilic glucose and amphiphilic stearic acid, onto a soil 19 mineral analogue (Al 2 O 3 ). Neutron reflectometry, a technique which provides depth-20 sensitive insight into the organization of the thin films, indicates that glucose 21 molecules reside in a layer between Al 2 O 3 and stearic acid, a result that was verified 22
ABSTRACT The development of ``spintronics'' devices based on charge and spin tran... more ABSTRACT The development of ``spintronics'' devices based on charge and spin transport has signaled a paradigm shift in the design of data storage and computing technologies. Magnetoelectric materials, which exhibit intrinsic coupling between electronic and magnetic order, are ideal for these applications. Unfortunately, single-phase magnetoelectrics are exceedingly rare in nature and attention has turned to composite heterostructures that display coupled functionalities at interfaces. A promising system in which to explore this coupling is a thin film oxide heterostructure of the piezoelectric Pb(Zr0.2Ti0.8)O3 (PZT) and the half-metal La0.7Sr0.3MnO3 (LSMO). We show that it is possible to construct a capacitor-type device structure from these materials that may form the basis for an electrically-switched magnetic memory. We conduct polarized neutron reflectometry (PNR) measurements and measure changes in the magnetization depth profile throughout the composite under the reversal of an in situ electric field. We then correlate these PNR results to local strain and chemistry using transmission electron microscopy (TEM). We find that a combination of charge doping and strain mechanisms governs coupling in this system.
ABSTRACT Early GMR devices relied on antiferromagnetic interlayer coupling to work and it was sho... more ABSTRACT Early GMR devices relied on antiferromagnetic interlayer coupling to work and it was shown that the interlayer coupling is in fact oscillatory, with both ferromagnetic and antiferromagnetic interlayer exchange depending on the thickness of the nonmagnetic layer [1,2]. Different competing interactions such as magnetic anisotropy and interlayer afm coupling occur in multilayer systems. Distinguishing the individual contributions is one of the major challenges in the study of multilayered systems. We used polarized neutron reflectivity with full polarization analysis to understand how the magnetization is distributed through the system and how deep the flipping process of the magnetization goes into the system. The easy axis field dependence of occurrence of spin-flop and spin-flip events in the system will be reported. [4pt] [1] S. S. P. Parkin, Phys. Rev. Lett. 71, 1641 (1993).[0pt] [2] D. Elefant, et al., Phys. Rev. B 77, 014426 (2008).
The voltage sensor domain (VSD) of voltage-gated cation (e.g., Na(+), K(+)) channels central to n... more The voltage sensor domain (VSD) of voltage-gated cation (e.g., Na(+), K(+)) channels central to neurological signal transmission can function as a distinct module. When linked to an otherwise voltage-insensitive, ion-selective membrane pore, the VSD imparts voltage sensitivity to the channel. Proteins homologous with the VSD have recently been found to function themselves as voltage-gated proton channels or to impart voltage sensitivity to enzymes. Determining the conformational changes associated with voltage gating in the VSD itself in the absence of a pore domain thereby gains importance. We report the direct measurement of changes in the scattering-length density (SLD) profile of the VSD protein, vectorially oriented within a reconstituted phospholipid bilayer membrane, as a function of the transmembrane electric potential by time-resolved X-ray and neutron interferometry. The changes in the experimental SLD profiles for both polarizing and depolarizing potentials with respect to zero potential were found to extend over the entire length of the isolated VSD's profile structure. The characteristics of the changes observed were in qualitative agreement with molecular dynamics simulations of a related membrane system, suggesting an initial interpretation of these changes in terms of the VSD's atomic-level 3-D structure.
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Papers by V. Lauter