Browsing by Author "Brück, S"
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- ItemElement-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, CDepth-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.
- ItemExchange bias in a nanocrystalline hematite/permalloy thin film investigated with polarized neutron reflectometry(American Physical Society, 2012-08-07) Cortie, DL; Lin, KW; Shueh, C; Hsu, HF; Wang, XL; James, M; Fritzsche, H; Brück, S; Klose, FWe investigated a hematite alpha-Fe2O3/permalloy Ni80Fe20 bilayer film where the antiferromagnetic layer consisted of small hematite grains in the 2 to 16 nm range. A pronounced exchange bias effect occurred below the blocking temperature of 40 K. The magnitude of exchange bias was enhanced relative to reports for identical compounds in large grain, epitaxial films. However, the blocking temperature was dramatically reduced. As the Neel temperature of bulk alpha-Fe2O3 is known to be very high (860 K), we attribute the low-temperature onset of exchange bias to the well-known finite-size effect which suppresses the Morin transition for nanostructured hematite. Polarized neutron reflectometry was used to place an upper limit on the concentration and length scale of a layer of uncompensated moments at the antiferromagnetic interface. The data were found to be consistent with an induced magnetic region at the antiferromagnetic interface of 0.5-1.0 mu(B) per Fe atom within a depth of 1-2 nm. The field dependence of the neutron spin-flip signal and spin asymmetry was analyzed in the biased state, and the first and second magnetic reversal were found to occur by asymmetric mechanisms. For the fully trained permalloy loop, reversal occurred symmetrically at both coercive fields by an in-plane spin rotation of ferromagnetic domains. © 2012, American Physical Society.
- ItemIntrinsic reduction of the ordered 4f magnetic moments in semiconducting rare-earth nitride thin films: DyN, ErN, and HoN(American Physical Society, 2014-02-26) Cortie, DL; Brown, JD; Brück, S; Saerbeck, T; Evans, JP; Fritzsche, H; Wang, XL; Downes, JE; Klose, FPolarized neutron reflectometry and x-ray reflectometry were used to determine the nanoscale magnetic and chemical depth profiles of the heavy rare-earth nitrides HoN, ErN, and DyN in the form of 15- to 40-nm-thick films. The net ferromagnetic components are much lower than the predictions of density-functional theory and Hund's rules for a simple ferromagnetic ground state in these 4f ionic materials, which points to the intrinsic contribution of crystal-field effects and noncollinear spin structures. The magnetic moment per rare-earth ion was determined as a function of temperature in the range 5–100 K at fields of 1–4 T. It is demonstrated that the films are stoichiometric within 1–3% and magnetically homogeneous on the nanometer scale.© 2014, American Physical Society.
- ItemLocal magnetic structure at the Fe3O4/ZnO interface(Australian Institute of Physics, 2012-02-01) Brück, S; Paul, M; Tian, H; Müller, A; Fauth, K; Goering, E; Verbeeck, J; Van Tendeloo, G; Claessen, RMagnetite, Fe3O4, is a half-metal with 100% spin polarization of the minority band at the Fermi level. This together with its good conductivity match to standard semiconductors makes it a promising candidate for polarized spin injection into semiconductor materials such as Si, GaAs, or ZnO [1]. An important aspect for such applications is the magnetism directly at the interface between Fe3O4 and the semiconductor. Soft x-ray resonant magnetic reflectometry is a technique which is capable of providing structural and magnetic depth profiles with 0.1nm resolution. We present a detailed XRMR and electron energy loss spectroscopy (STEM/EELS) study of an epitaxial Fe3O4 thin film grown directly on a semiconducting ZnO substrate [2]. Consistent chemical profiles at the interface between ZnO and Fe3O4 are found from XRMR and EELS. The magnetic depth profile of tetragonal Fe3+ and octahedral Fe2+ ions in Fe3O4 is derived with monolayer resolution and reveals a change in the Fe stoichiometry directly at the interface.
- ItemPolarized neutron reflectometry of rare-earth nitride thin films(Australian Institute of Physics, 2012-02-02) Brück, S; Cortie, DL; Brown, J; Saerbeck, T; Ulrich, C; Klose, F; Downes, JRare-earth monopnictides like HoN, DyN, or ErN are semiconductors with typical band gaps between 0.73 and 1.3eV. The fact that they exhibit ferromagnetic ordering at low temperatures makes them possible candidates for an intrinsically ferromagnetic semiconductor [1]. Thin, polycrystalline rare-earth nitride films of 15 – 40nm thickness were grown onto c-plane sapphire substrates using low-energy ion assisted deposition. A temperature- and field-dependent polarized neutron reflectometry study in combination with SQUID magnetometry was carried out to characterize the magnetic properties of these films in a depth resolved way. The investigated samples show a homogeneous distribution of the magnetic moment throughout the film with ferromagnetic ordering temperatures comparable to the bulk materials. ErN and HoN films do not show an opening of the magnetic hysteresis loop even for the lowest measured temperature of T=2K. DyN on the other hand clearly shows a coercive field and remnant magnetization at 5K.
- ItemTime-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, FTime-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.