Browsing by Author "Lott, D"
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- ItemAntiferromagnetism in a Fe50Pt40Rh10 thin film investigated using neutron diffraction(American Physical Society, 2008-11) Lott, D; Fenske, J; Schreyer, A; Mani, P; Mankey, GJ; Klose, F; Schmidt, W; Schmalzl, K; Tartakovskaya, EVThe temperature-dependent magnetic structure of a 200 nm thick single-crystalline film of Fe50Pt40Rh10 was studied by unpolarized and polarized neutron diffractions. By applying structure factor calculations, a detailed model of the magnetic unit cell was developed. In contrast to former studies on bulk samples, our experimental results show that the film remains in an antiferromagnetic state throughout the temperature range of 10–450 K. Remarkably, it can be demonstrated that the antiferromagnetic structure undergoes a smooth transition from a dominant out-of-plane order with the magnetic moments orientated in-plane to an in-plane order with the magnetic moments orientated perpendicular to the film plane. Theoretically this can be explained by the existence of two competing anisotropy contributions with different temperature dependencies. © 2008, American Physical Society
- 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
- ItemChemical-order-induced magnetic exchange bias in epitaxial FePt3 films(American Physical Society, 2008-04-11) Lott, D; Klose, F; Ambaye, H; Mankey, GJ; Mani, P; Wolff, M; Schreyer, A; Christen, HM; Sales, BCWe show that magnetic exchange bias can be induced by means of chemical ordering. The effect was observed on epitaxial thin film layers of FePt3, a material which has the remarkable property that, depending on the degree of chemical order, a ferromagnetic and an antiferromagnetic magnetic state can coexist at the same temperature. We demonstrate that the observed exchange bias originates at the interfaces between these two different magnetic phases of FePt3. © 2008, American Physical Society
- 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.
- 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 [1]. 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 [2]. 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 [2]). 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
- 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
- ItemStructural and magnetic properties of epitaxial Fe25Pt75(American Vacuum Society, 2009-07) Lu, Z; Walock, MJ; LeClair, PR; Mankey, GJ; Mani, P; Lott, D; Klose, F; Ambaye, H; Lauter, V; Wolff, M; Schreyer, A; Christen, HM; Sales, BCEpitaxial films of Fe25Pt75 have a number of different magnetic phases as a function of temperature and chemical order. For example, chemically ordered epitaxial films have two distinct antiferromagnetic phases at temperatures below similar to 160 K and exhibit paramagnetism above that temperature. In sharp contrast, chemically disordered epitaxial films are ferromagnetic with a Curie temperature that is greater than 400 K. It is demonstrated that by varying the substrate temperature during growth, epitaxial films with varying degrees of chemical order can be produced and it is possible to produce an alloy with the same composition throughout the film with a modified magnetic structure. The authors used polarized neutron reflectivity to gauge the magnetism of a Fe25Pt75 sample produced with a periodic variation in the growth temperature and showed that the sample exhibits a reduced Curie temperature of approximately 300 K as compared to bulk Fe25Pt75. © 2009, American Vacuum Society
- 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.