Browsing by Author "Saerbeck, T"
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- ItemArtificially modulated chemical order in thin films: a different approach to create ferro/antiferromagnetic interfaces(American Physical Society, 2010-10-06) Saerbeck, T; Klose, F; Lott, D; Mankey, GJ; Lu, Z; LeClair, PR; Schmidt, W; Stampfl, APJ; Danilkin, SA; Yethiraj, M; Schreyer, AWe report on a unique magnetic exchange interaction in a thin film of FePt3, comprising an artificially created ferromagnetic (FM)/antiferromagnetic (AFM) modulation, but homogeneous chemical composition and epitaxy throughout the film. The chemical order, on the other hand, is modulated resulting in the formation of alternating FM/AFM layers. To determine the existence and form of the magnetic structure within the monostoichiometric thin film, we use a unique combination of polarized neutron reflectometry, x-ray/neutron diffraction, and conventional magnetometry. This artificial stratified AFM/FM FePt3 exhibits a high magnetic exchange bias thus opening up possibilities to study such magnetic phenomena in a perfectly lattice-matched system. © 2010, 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.
- ItemThe multipurpose time-of-flight neutron reflectometer "Platypus" at Australia's OPAL reactor(Elsevier Science BV, 2011-03-11) James, M; Nelson, A; Holt, SA; Saerbeck, T; Hamilton, WA; Klose, FIn this manuscript we describe the major components of the Platypus time-of-flight neutron reflectometer at the 20 MW OPAL reactor in Sydney, Australia. Platypus is a multipurpose spectrometer for the characterisation of solid thin films, materials adsorbed at the solid-liquid interface and free-liquid surfaces. It also has the capacity to study magnetic thin films using spin-polarised neutrons. Platypus utilises a white neutron beam (lambda=2-20 angstrom) that is pulsed using boron-coated disc chopper pairs; thus providing the capacity to tailor the wavelength resolution of the pulses to suit the system under investigation. Supermirror optical components are used to focus, deflect or spin-polarise the broad bandwidth neutron beams, and typical incident spectra are presented for each configuration. A series of neutron reflectivity datasets are presented, indicating the quality and flexibility of this spectrometer. Minimum reflectivity values of <10(-7) are observed: while maximum thickness values of 325 nm have been measured for single-component films and 483 nm for a multilayer system. Off-specular measurements have also been made to investigate in-plane features as opposed to those normal to the sample surface. Finally, the first published studies conducted using the Platypus time-of-flight neutron reflectometer are presented. (C) 2011 Elsevier B.V. All rights reserved.
- ItemA new approach to the creation of magnetically modulated structures(Australian Institute of Physics, 2010-02-03) Saerbeck, T; Klose, F; Lott, D; Mankey, GJ; Lu, Z; LeClair, PR; Stampfl, APJ; Danilkin, SA; Yethiraj, M; Schreyer, AThe plethora of structural and magnetic properties observed in many transition metal alloys has attracted a great deal of interest in both the pure and applied sciences . One key attribute of these alloys is that their electronic and magnetic properties are extremely sensitive to not only stoichiometry but order as well. In this paper we report on a new approach of creating a magnetically modulated structure, without changing composition or lattice structure, namely by artificially controlling the degree of chemical order in the material. The compound FePt3, as it is well known from bulk crystals, has the extraordinary property to evolve ferromagnetic (FM) or antiferromagnetic (AFM) phases determined by the degree of chemical ordering . We succeeded in preparing epitaxial FePt3 superlattices of homogeneous composition consisting of an artificially modulated ferro/antiferromagnetic layering sequence simply by alternating the growth temperature. A direct effect of such an exotic FM/AFM interface is the observation of a high exchange bias upon field cooling through the Nèel temperature. In order to quantify the degree of antiferromagnetic ordering, high angle neutron diffraction has been performed using the triple axis spectrometer IN12 (Institute Laue Langevin, Grenoble) and TAIPAN (Australian Nuclear Science and Technology Organisation). Similar to chemically ordered bulk FePt3 the superlattice exhibits the onset of a (½ ½ 0) AFM Bragg peak below a temperature of TN=140 K (Bulk TN=160 K ). Using the polarized neutron reflectometry technique at the German research facility GKSS, Geesthacht, a detailed layer resolved magnetic characterization of the superlattice was carried out.
- ItemOnset of biquadratic coupling in Co/CuMn multilayers studied with polarised neutron reflectivity(Australian Institute of Physics, 2009-02-05) Loh, NA; Saerbeck, T; Ali, M; Lott, D; Stampfl, APJ; Hickey, BJ; Toperverg, BP; Mulders, AM; Stamps, RL; Klose, FNot available
- ItemPolarization "down under": the polarized time-of-flight neutron reflectometer PLATYPUS(American Institute of Physics, 2012-08-01) Saerbeck, T; Klose, F; Le Brun, AP; Füzi, J; Brûlé, A; Nelson, A; Holt, SA; James, MThis review presents the implementation and full characterization of the polarization equipment of the time-of-flightneutron reflectometer PLATYPUS at the Australian Nuclear Science and Technology Organisation (ANSTO). The functionality and efficiency of individual components are evaluated and found to maintain a high neutron beam polarization with a maximum of 99.3% through polarizing Fe/Si supermirrors. Neutron spin-flippers with efficiencies of 99.7% give full control over the incident and scattered neutron spin direction over the whole wavelength spectrum available in the instrument. The first scientific experiments illustrate data correction mechanisms for finite polarizations and reveal an extraordinarily high reproducibility for measuring magnetic thin film samples. The setup is now fully commissioned and available for users through the neutron beam proposal system of the Bragg Institute at ANSTO. © 2012, American Institute of Physics.
- 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 . 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.
- ItemSpatial fluctuations of loose spin coupling in CuMn/Co multilayers(American Physical Society, 2011-09-12) Saerbeck, T; Loh, NA; Lott, D; Toperverg, BP; Mulders, AM; Rodriguez, AF; Freeland, JW; Ali, M; Hickey, BJ; Stampfl, APJ; Klose, F; Stamps, RLA detailed investigation of magnetic impurity-mediated interlayer exchange coupling observed in Cu(0.94)Mn(0.06)/Co multilayers using polarized neutron reflectometry and magnetic x-ray techniques is reported. Excellent descriptions of temperature and magnetic field dependent biquadratic coupling are obtained using a variant of the loose spin model that takes into account the distribution of the impurity Mn ions in three dimensions. Positional disorder of the magnetic impurities is shown to enhance biquadratic coupling via a new contribution J(2)(fluct), leading to a temperature dependent canting of magnetic domains in the multilayer. These results provide measurable effects on RKKY coupling associated with the distribution of impurities within planes parallel to the interfaces.© 2011, American Physical Society
- ItemStudying 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, CBismuth 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 . 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 . Epitaxial (001) BiFeO3 / La0.67Sr0.33MnO3 (LSMO) multiferroic tunnel junctions have been grown by pulsed laser deposition at the University of NSW . 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 . 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.
- ItemTailoring exchange bias through chemical order in epitaxial FePt3 films(AIP Publishing, 2013-01-01) Saerbeck, T; Zhu, HL; Lott, D; Lee, H; LeClair, PR; Mankey, GJ; Stampfl, APJ; Klose, FIntentional introduction of chemical disorder into mono-stoichiometric epitaxial FePt3 films allows to create a ferro-/antiferromagnetic two-phase system, which shows a pronounced and controllable exchange bias effect. In contrast to conventional exchange bias systems, granular magnetic interfaces are created within the same crystallographic structure by local variation of chemical order. The amount of the exchange bias can be controlled by the relative amount and size of ferromagnetic and antiferromagnetic volume fractions and the interface between them. The tailoring of the magnetic composition alone, without affecting the chemical and structural compositions, opens the way to study granular magnetic exchange bias concepts separated from structural artifacts. © 2013, American Institute of Physics.
- ItemTemperature dependent biquadratic exchange coupling in Co/Cu (0.94)Mn(0.06) multilayers(Australian Institute of Physics, 2010-02-05) Saerbeck, T; Loh, NA; Ali, M; Hickey, BJ; Lott, D; Toperverg, BP; Mulders, AM; Stampfl, APJ; Klose, F; Stamps, RLMagnetic interlayer coupling phenomena in systems consisting of ferromagnetic films separated by non-magnetic spacer layers, such as Co/Cu multilayers, are heavily dependent on the thickness and composition of the spacer layer. Usual Co/Cu multilayers exhibit the normal oscillatory RKKY exchange coupling resulting in alternating ferromagnetic/antiferromagnetic magnetic alignment of adjacent layers with increasing Cu thickness. We report on a crucial temperature dependence of this coupling introduced as the non-magnetic spacer layer is substituted by a spin-glass material, such as CuMn. Kobayashi et al. first discovered the extraordinary behaviour of a ferromagnetic exchange coupled Co/CuMn multilayer structure showing an increasing antiferromagnetic component as the system is cooled below a critical temperature. In order to investigate the magnetic rearrangement throughout the transition temperature in more detail we used polarized neutron reflectometry in specular and off-specular geometry to resolve the orientation of the magnetization in the Co layers. Co/Cu(0.94)Mn(0.06) multilayer samples with a manganese concentration of 6at% in the spacer layer are grown using sputter deposition and quality checked with X-ray reflectivity and diffraction. The onset of a magnetic rearrangement into an antiferromagnetic constitution around 100K is confirmed by neutron reflectivity measurements, revealing the onset of biquadratic interlayer coupling. Simulations of the full two dimensional off-specular scattering points out each layer breaking into magnetic domains. Further magnetic characterisation of the sample using X-Ray magnetic circular dichroism and conventional magnetometry indicate the role of the Mn doping in the magnetic transition into a biquadratic coupling.
- 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.