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Browsing by Author "Bertinshaw, J"

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90° magnetic coupling in a NiFe/FeMn/biased NiFe multilayer spin valve component investigated by polarized neutron reflectometry
(American Institute of Physics, 2014-07-17) Callori, SJ; Bertinshaw, J; Cortie, DL; Cai, JW; Le Brun, AP; Zhu, T; Klose, F
We have observed 90° magnetic coupling in a NiFe/FeMn/biased NiFe multilayer system using polarized neutron reflectometry. Magnetometry results show magnetic switching for both the biased and free NiFe layers, the latter of which reverses at low applied fields. As these measurements are only capable of providing information about the total magnetization within a sample, polarized neutron reflectometry was used to investigate the reversal behavior of the NiFe layers individually. Both the non-spin-flip and spin-flip neutron reflectometry signals were tracked around the free NiFe layer hysteresis loop and were used to detail the evolution of the magnetization during reversal. At low magnetic fields near the free NiFe coercive field, a large spin-flip signal was observed, indicating magnetization aligned perpendicular to both the applied field and pinned layer. © 2020 AIP Publishing LLC.
Complex magnetic structure in strained nanoscale bismuth ferrite thin films
(Australian Institute of Physics, 2016-02-02) Ulrich, C; Bertinshaw, J; Maran, R; Callori, SJ; Ramesh, V; Cheng, J; Danilkin, SA; Hu, S; Siedel, J; Valanoor, N
Multiferroic materials demonstrate excellent potential for next-generation multifunctional devices, as they exhibit coexisting ferroelectric and magnetic orders. Bismuth ferrite (BiFeO3) is a rare exemption where both order parameters coexist far beyond room temperature, making it the ideal candidate for technological applications. In particular, multiferroic thin films are the most promising pathway for spintronics applications. Therefore we have investigated BiFeO3 thin films by neutron diffraction. At present, the underlying physics of the magnetoelectric coupling is not fully understood and competing theories exist with partly conflicting predictions. For example, the existence of spin cycloid is a mandatory requirement to establish a direct magnetoelectric coupling. Thus far internal strain in epitaxially grown films has limited the stability of the spin cycloid for BiFeO3 films with less than 300 nm thickness, causing the spin cycloid to collapses to a collinear G-type antiferromagnetic structure. Our neutron diffraction experiments have demonstrated that we were able to realize a spin cycloid in films of just 100 nm thickness through improved electrostatic and epitaxial constraints. This underlines the importance of the correct mechanical and electrical boundary conditions required to achieve emergent spin properties in mutiferroic thin film systems. The discovery of a large scale uniform cycloid in thin film BiFeO3 opens new avenues for fundamental research and technical applications that exploit the spin cycloid in spintronic or magnonic devices.
Direct evidence for the spin cycloid in strained nanoscale bismuth ferrite thin films
(Australian Institute of Physics, 2017-01-31) Bertinshaw, J; Maran, R; Callori, SJ; Ramesh, V; Cheung, J; Dainlkin, SA; Lee, WT; Hu, S; Seidel, J; Valanoor, N; Ulrich, C
Multiferroic materials demonstrate excellent potential for next-generation multifunctional devices, as they exhibit coexisting ferroelectric and magnetic orders. Bismuth ferrite (BiFeO3) is a rare exemption where both order parameters exist far beyond room temperature, making it the ideal candidate for technological applications. In particular, magnonic devices that utilize electric control of spin waves mediated by complex spin textures are an emerging direction in spintronics research. To realize magnonic devices, a robust long-range spin cycloid with well known direction is desired, since it is a prerequisite for the magnetoelectric coupling. Despite extensive investigation, the stabilization of a large-scale uniform spin cycloid in nanoscale (100 nm) thin BiFeO3 films has not been accomplished. Here, we demonstrate cycloidal spin order in 100 nm BiFeO3 thin films through the careful choice of crystallographic orientation, and control of the electrostatic and strain boundary conditions during growth [1]. Neutron diffraction, in conjunction with X-ray diffraction, reveals an incommensurate spin cycloid with a unique [112] propagation direction. While this direction is different from bulk BiFeO3, the cycloid length and Néel temperature remain equivalent to bulk single crystals. The discovery of a large scale uniform cycloid in thin film BiFeO3 opens new avenues for fundamental research and technical applications that exploit the spin cycloid in spintronic or magnonic devices.
Element-specific depth profile of magnetism and stoichiometry at the La0.67Sr0.33MnO3/BiFeO3 interface
(American Physical Society, 2014-07-11) Bertinshaw, J; Brück, S; Lott, D; Fritzsche, H; Khaydukov, Y; Soltwedel, O; Keller, T; Goering, E; Audehm, P; Cortie, DL; Hutchison, WD; Ramasse, QM; Arredondo, M; Maran, R; Nagarajan, V; Klose, F; Ulrich, C
Depth-sensitive magnetic, structural, and chemical characterization is important in the understanding and optimization of physical phenomena emerging at the interfaces of transition metal oxide heterostructures. In a simultaneous approach we have used polarized neutron and resonant x-ray reflectometry to determine the magnetic profile across atomically sharp interfaces of ferromagnetic La0.67Sr0.33MnO3/multiferroic BiFeO3 bilayers with subnanometer resolution. In particular, the x-ray resonant magnetic reflectivity measurements at the Fe and Mn resonance edges allowed us to determine the element-specific depth profile of the ferromagnetic moments in both the La0.67Sr0.33MnO3 and BiFeO3 layers. Our measurements indicate a magnetically diluted interface layer within the La0.67Sr0.33MnO3 layer, in contrast to previous observations on inversely deposited layers [P. Yu et al., Phys. Rev. Lett. 105, 027201 (2010)]. Additional resonant x-ray reflection measurements indicate a region of altered Mn and O content at the interface, with a thickness matching that of the magnetic diluted layer, as the origin of the reduction of the magnetic moment.© 2014, American Physical Society.
Evolution of magnetic phase and cation distribution in Cu1-xZnxFe2O4 studied by neutron powder diffraction
(Australian Institute of Physics, 2015-02-06) Chang, FF; Deng, DC; Avdeev, M; Hester, JR; Bertinshaw, J; Ulrich, C
CuFe2O4 is a highly interesting material as it is a ferrimagnet with an unusual high magnetic ordering temperature of 780 K. ZnFe2O4, on the other hand, is a frustrated spin system with antiferromagnetic order below 10 K. By doping nonmagnetic Zn ions in CuFe2O4, frustration can be introduced and interesting properties might emerge. Given that, high resolution and high intensity neuron powder diffraction techniques have been applied to study the structural and magnetic phase transition in Cu1-xZnxFe2O4 from 4 K to 750 K. Coexistence of cubic and tetragonal structure in CuFe2O4 was observed in a wide temperature range, which indicates a second order phase transition nature. This transition is caused by Jahn-Teller distortion of the CuO6 octahedra. Although CuFe2O4 and ZnFe2O4 are inverse and normal spinels, respectively, mixed cation distribution was found in doped samples, with Cu and Zn ions sitting both either on the tetrahedral or the octahedral sites. All the doped Cu1-xZnxFe2O4 (x = 0.2 - 1) samples crystallise in the cubic structure and order in the ferrimagnetic spin configuration. Upon doping, the value of oxygen position parameter μ increases, indicating the compression of the octahedra with increasing Zn-composition. Short-range antiferromagnetic order was observed below 10 K in cubic ZnFe2O4. The spin frustration, which leads to the antiferromagnetic order in Cu0.04Zn0.96Fe2O4 and ZnFe2O4 is induced by the competing interaction between the first nearest neighbor and the third nearest neighbour tetrahedra formed by Fe ions on B sites.
FeCr2S4 in magnetic fields: possible evidence for a multiferroic ground state
(Nature.com, 2014-08-15) Bertinshaw, J; Ulrich, C; Günther, A; Schrettle, F; Wohlauer, M; Krohns, S; Reehuis, M; Studer, AJ; Avdeev, M; Quach, DV; Groza, JR; Tsurkan, V; Loidl, A; Deisenhofer. J.
We report on neutron diffraction, thermal expansion, magnetostriction, dielectric, and specific heat measurements on polycrystalline FeCr2S4 in external magnetic fields. The ferrimagnetic ordering temperatures TC ≈ 170 K and the transition at TOO ≈ 10 K, which has been associated with orbital ordering, are only weakly shifted in magnetic fields up to 9 T. The cubic lattice parameter is found to decrease when entering the state below TOO. The magnetic moments of the Cr- and Fe-ions are reduced from the spin-only values throughout the magnetically ordered regime, but approach the spin-only values for fields >5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample below about 60 K. Below TOO this contraction is followed by a moderate expansion of the sample for fields larger than ~4.5 T. The transition at TOO is accompanied by an anomaly in the dielectric constant. The dielectric constant depends on both the strength and orientation of the external magnetic field with respect to the applied electric field for T < TOO. A linear correlation of the magnetic-field-induced change of the dielectric constant and the magnetic-field dependent magnetization is observed. This behaviour is consistent with the existence of a ferroelectric polarization and a multiferroic ground state below 10 K. © The Authors
Neutron diffraction, magnetostriction, and dielectric properties of orbitally ordered FeCr2S4 in external magnetic fields
(arXiv, 2013-09-09) Bertinshaw, J; Ulrich, C; Günther, A; Schrettle, F; Wohlauer, M; Krohns, S; Reehuis, M; Studer, AJ; Avdeev, M; Quach, DV; Groza, JR; Tsurkan, V; Loidl, A; Deisenhofer, J
We report on neutron diffraction, thermal expansion, dielectric and specific heat measurements on polycrystalline FeCr2S4 samples in external magnetic fields. The ferrimagnetic and orbital ordering temperatures, T_C = 170K and T_OO = 10 K are only weakly shifted in magnetic fields up to 9 T. The cubic lattice parameter is found to decrease when entering the orbitally ordered state below T_OO. This contraction does not significantly change in external fields up to 7.5 T. The magnetic moments of the Cr and Fe ions are reduced from the spin-only values throughout the magnetically ordered regime. The moments start to increase in the orbitally ordered regime when the magnetic fields become larger than 4.5 T and approach the expected spin-only values above about 5.5 T. Thermal expansion in magnetic fields and magnetostriction experiments indicate a contraction of the sample due to magnetic domains below about 60 K. In the orbitally ordered state this contraction is followed by a moderate expansion of the sample for fields larger than about 4.5 T, coinciding with the onset of the increase of the magnetic moments. The orbital ordering transition is accompanied by an anomaly in the dielectric constant. Below T_OO the dielectric constant depends on both the strength of the external magnetic field as well as the orientation of the external magnetic field with respect to the applied electric field.
Polarised neutron diffraction study of the spin cycloid in strained nanoscale bismuth ferrite thin films
(Australian Institute of Physics, 2017-01-31) Lee, WT; Bertinshaw, J; Maran, R; Callori, SJ; Ramesh, V; Cheung, J; Danilkin, SA; Hu, S; Seidel, J; Valanoor, N; Ulrich, C
Polarised neutron scattering is capable of separating magnetic structure from chemical structure. Here we report an experiment using the newly available capability at ANSTO, namely polarised neutron diffraction using polarised 3He neutron spin-filters to obtain the detail magnetic structure in even highly complex magnetic materials. Magnonic devices that utilize electric control of spin waves mediated by complex spin textures are an emerging direction in spintronics research. Room-temperature multiferroic materials, such as BiFeO3, with a spin cycloidal structure would be ideal candidates for this purpose. In order to realise magnonic devices, a robust long-range spin cycloid with well-known direction is desired. Despite extensive investigation, the stabilization of a large scale uniform spin cycloid in nanoscale (100 nm) thin BiFeO3 films has not been accomplished. The polarized neutron diffraction experiment did confirm the existence of the spin cycloid in this BiFeO3 film, which is an important prerequisite for the multiferroic coupling.
Radiation damage in anatase and rutile with impurities
(Australian Institute of Physics, 2009-02-04) Bertinshaw, J; Aughterson, RD; Thorogood, GJ; Short, KT; Whittle, KR
Not available
Spin-cycloid instability as the origin of weak ferromagnetism in the disordered perovskite Bi0.8La0.2Fe0.5Mn0.5O3
(American Physical Society, 2014-04-23) Bertinshaw, J; Cortie, DL; Cheng, ZX; Avdeev, M; Studer, AJ; Klose, F; Ulrich, C; Wang, XL
Powder neutron diffraction and magnetometry studies have been conducted to investigate the crystallographic and magnetic structure of Bi0.8La0.2Fe0.5Mn0.5O3. The compound stabilizes in the Imma orthorhombic crystal symmetry in the measured temperature range of 5 to 380 K, with a transition to antiferromagnetic order at TN≈240 K. The spin cycloid present for BiFeO3 is found to be absent with 50% Mn3+ cation substitution, leading to G-type antiferromagnetic order with an enhanced out-of-plane canted ferromagnetic component, evident from measurable weak-ferromagnetic hysteresis. Structural modifications do not solely explain this behavior, indicating that modified electron exchange interactions must be taken into account. A classical spin simulation was developed to investigate the effect of random substitution in a disordered pseudocubic perovskite. The calculations took into account the nearest-neighbor, next-nearest-neighbor, and Dzyaloshinskii-Moriya interactions, along with the local spin anisotropy. Using this framework to extend the established Hamiltonian model for BiFeO3, we show that only certain types of perturbations at a magnetic defect and the surrounding molecular fields trigger a simultaneous collapse of cycloidal order and the emergence of the long-range weak-ferromagnetic component. By adopting values for the Mn molecular fields appropriate for REMnO3 (RE= rare earth), simulations of BiMn0.5Fe0.5O3 exhibit the key magnetic properties of our experimental observations.© 2014, American Physical Society.
Stability and scaling behavior of the spin cycloid in BiFeO3 thin films
(Australian Institute of Physics, 2018-01-30) Burns, SR; Sando, D; Bertinshaw, J; Russell, L; Xu, X; Maran, R; Callori, SJ; Ramash, V; Cheung, J; Danilkin, SA; Deng, G; Lee, WT; Hu, S; Bellaiche, L; Seidel, J; Valanoor, N; Ulrich, C
Multiferroic materials demonstrate excellent potential for next-generation multifunctional devices, as they exhibit coexisting ferroelectric and magnetic orders. Bismuth ferrite (BiFeO3) is a rare exemption where both order parameters exist far beyond room temperature, making it the ideal candidate for technological applications. To realize magnonic devices, a robust longrange spin cycloid with well-known direction is desired, since it is a prerequisite for the magnetoelectric coupling. Despite extensive investigation, the stabilization of a large-scale uniform spin cycloid in nanoscale (<300 nm) thin BiFeO3 films has not been accomplished. Using neutron diffraction we were able to demonstrate cycloidal spin order in 100 nm BiFeO3 thin films which became stable through the careful choice of crystallographic orientation and control of the electrostatic and strain boundary conditions during growth [1]. Furthermore, Co-doping, which has demonstrated to further stabilize the spin cycloid, did allow us to obtain spin cycloid order in films of just 50 nm thickness, i.e. films thinner than the cycloidal length of about 64 nm. Interestingly, in thin films the propagation direction of the spin cycloid has changed and shows a peculiar scaling behavior for thinnest films. We were able to support these observations by Monte Carlo theory based on a first-principles effective Hamiltonian method. Our results therefore offer new avenues for fundamental research and technical applications that exploit the spin cycloid in spintronic or magnonic devices.
Strain-induced magnetic phase transition in SrCoO3 thin films
(Australian Institute of Physics, 2015-02-06) Callori, SJ; Hu, S; Bertinshaw, J; Yue, ZJ; Danilkin, SA; Wang, XL; Nagarajan, V; Klose, F; Seidel, J; Ulrich, C
Transition metal oxides represent a wide set of materials with a broad range of functionalities, including superconductivity, magnetism, and ferroelectricity, which can be tuned by the careful choice of parameters such as strain, oxygen content, and applied electric or magnetic fields. This tunability makes them ideal candidate materials for use in developing novel information and energy technologies. SrCoO3 provides a particularly interesting system for these investigations. Lee and Rabe have simulated the effect of strain and have predicted that the magnetic state can be tuned through compressive or tensile strain with a ferromagnetic-antiferromagnetic phase transition. Such a phase transition would be accompanied by a metal-to-insulator phase transition and a transition to a ferroelectric polarised state. We have achieved large in-plane tensile strain in SrCoO3 thin films through the proper choice of substrate and our neutron diffraction experiments on only 40 nm thick films have indeed confirmed the transition from a ferromagnetic to an antiferromagnetic ground state, as theoretically predicted. As such, SrCoO3 would constitute a new class of multiferroic material where magnetic and electric polarisations can be driven through external strain.
Strain-induced magnetic phase transition in SrCoO3−δ thin films
(American Physical Society, 2015-04-10) Callori, SJ; Hu, S; Bertinshaw, J; Yue, ZJ; Danilkin, SA; Wang, XL; Nagarajan, V; Klose, F; Seidel, J; Ulrich, C
It has been well established that both in bulk at ambient pressure and for films under modest strains, cubic SrCoO3−δ (δ<0.2) is a ferromagnetic metal. Recent theoretical work, however, indicates that a magnetic phase transition to an antiferromagnetic structure could occur under large strain accompanied by a metal-insulator transition. We have observed a strain-induced ferromagnetic-to-antiferromagnetic phase transition in SrCoO3−δ films grown on DyScO3 substrates, which provide a large tensile epitaxial strain, as compared to ferromagnetic films under lower tensile strain on SrTiO3 substrates. Magnetometry results demonstrate the existence of antiferromagnetic spin correlations and neutron diffraction experiments provide a direct evidence for a G-type antiferromagnetic structure with Neél temperatures between TN∼135±10K and ∼325±10K, depending on the oxygen content of the samples. Therefore, our data experimentally confirm the predicted strain-induced magnetic phase transition to an antiferromagnetic state for SrCoO3−δ thin films under large epitaxial strain. © 2015 American Physical Society.
Studying multiferroic BiFeO3 and ferromagnetic La0.67Sr0.33MnO3 tunnel junctions with Raman spectroscopy and neutron scattering techniques
(Australian Institute of Physics, 2011-02-02) Bertinshaw, J; Saerbeck, T; Nelson, A; James, M; Nagarajan, V; Klose, F; Ulrich, C
Bismuth Ferrite (BiFeO3 or BFO) is a prominent multiferroic material candidate for industrial implementation as it is among one of the rare cases where ferroelectric polarisation and magnetic order coexist at room temperature [1]. We have investigated its potential in functional thin film heterostructures, where it is possible the interplay between FE and FM at the interface between layers can enable controllable magnetoelectric coupling, allowing for the control of the magnetic polarisation through applied electric fields and vice-versa [2]. Epitaxial (001) BiFeO3 / La0.67Sr0.33MnO3 (LSMO) multiferroic tunnel junctions have been grown by pulsed laser deposition at the University of NSW [3]. These trilayer systems layer: 40nm of LSMO, 10nm of BFO, and 40nm of LSMO on a SrTiO3 substrate, with a RMS roughness of not more than one unit cell. We have found initial experimental evidence of a correlation between the spin polarisation of the FM LSMO layers and the FE polarisation of the BiFeO3 layer through flips in the domain structure through a number of electrical resistance based experimental techniques [3]. We plan to combine results from Raman spectroscopy conducted at the UNSW with polarised neutron reflectometry on PLATYPUS and inelastic neutron scattering on TAIPAN at the Bragg Institute, ANSTO to perform a detailed analysis of: the magnetisation reversal process in the LSMO contact layers, the interplay (exchange bias) between the BFO AFM and LSMO FM parameters, the magnetic depth profile of the heterostructure, in particular the interface regions, and the effect of switching the electric polarisation of the BiFeO3 layer on the domain wall structure, and therefore on the magnetic structure of the entire thin film system.
Time-of-flight polarized neutron reflectometry on PLATYPUS: status and future developments
(Elsevier, 2013-04-23) Saerbeck, T; Cortie, DL; Brück, S; Bertinshaw, J; Holt, SA; Nelson, A; James, M; Lee, WT; Klose, F
Time-of-flight (ToF) polarized neutron reflectometry enables the detailed investigation of depth-resolved magnetic structures in thin film and multilayer magnetic systems. The general advantage of the time-of-flight mode of operation over monochromatic instruments is a decoupling of spectral shape and polarization of the neutron beam with variable resolution. Thus, a wide Q-range can be investigated using a single angle of incidence, with resolution and flux well-adjusted to the experimental requirement. Our paper reviews the current status of the polarization equipment of the ToF reflectometer PLATYPUS and presents first results obtained on stratified Ni80Fe20/α-Fe2O3 films, revealing the distribution of magnetic moments in an exchange bias system. An outlook on the future development of the PLATYPUS polarization system towards the implementation of a polarized 3He cell is presented and discussed with respect to the efficiency and high Q-coverage up to 1 Å−1 and 0.15 Å−1 in the vertical and lateral momentum transfer, respectively. © 2013, Elsevier Ltd.

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