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Browsing by Author "Klose, F"

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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.
90° magnetic coupling in a NiFe/FeMn/biased NiFe spin valve investigated by polarised neutron reflectometry
(Australian Institute of Physics, 2014-02-05) Callori, SJ; Zhu, T; Klose, F
We have used the PLATYPUS reflectometer at ANSTO to perform polarised neutron reflectometry in order to investigate 90° magnetic coupling in a Ni81Fe19/Fe50Mn50/biased Ni81Fe19 spin valve system. Spin valves play an important role in current and developing technological systems, such as spintronics devices or magnetoresistive sensors. For the later usage, perpendicular coupling in a spin valve structure leads to a desired linear, reversible resistance response to an applied magnetic field. The spin valve presented here consists of both free and exchange biased ferromagnetic Ni81Fe19 layers, the later of which is pinned by an antiferromagnetic Ir25Mn75 layer at low applied magnetic fields. The free Ni81Fe19 may be magnetically reversed under low fields, and standard magnetometry measurements on similar systems have suggested perpendicular orientation of the free and biased magnetisations at zero field. Magnetometry measurements, however, are only capable of providing information about the magnetisation within a sample along the direction of the applied field. In contrast, polarised neutron reflectometry (PNR) is capable of resolving the in-plane magnetisation vectors both along and perpendicular to the applied magnetic field as function of layer depth. Here, PNR was used to obtain magnetic vector depth profiles of the spin valve at several applied fields, including low fields near the switching point of the free Ni81Fe19 layer. At these fields a large spin-flip signal was observed in the free layer, indicating magnetisation aligned perpendicular to the external field applied along the pinned layer magnetisation. Both the non-spin flip and spin-flip signals were also tracked around the free layer hysteresis loops and can be used to map the evolution of the free Ni81Fe19 layer during magnetic reversal.
Advancing the reflectometry cause at ANSTO - updates and upgrades to the time-of-flight Platypus Neutron Reflectometer.
(International Conference on Neutron Scattering, 2017-07-12) Nelson, A; Holt, SA; Darmann, F; Klose, F
Since the first suite of neutron scattering instruments was commissioned in 2008 the Australian Nuclear Science and Technology Organisation (ANSTO) has invested in instrumentation for the analysis of thin interfacial films. The horizontal time-of-flight reflectometer, Platypus [1], has now been joined by an X-ray reflectometer and a variable angle spectroscopic imaging ellipsometer. The high quality science possible on these complementary instruments has lead to a large oversubscription rate on Platypus. Here, we outline the key developments and upgrades we have made to Platypus that have led to this success. These include the development of event mode acquisition for studying kinetic processes, new sample environments (confinement cell, vapour delivery systems), as well as projects to upgrade its performance by installing new collimation systems and detectors.
Antiferromagnetism 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, EV
The 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
Artificially 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, A
We 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
Chemical-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, BC
We 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
Correlating uncompensated antiferromagnetic moments and exchange coupling interactions in interface ion-beam bombarded Co90Fe10/CoFe-oxide bilayers
(IOP Publishing LTD, 2012-11-01) Shueh, C; Chen, PS; Cortie, DL; Klose, F; Chen, WC; Wu, TH; van Lierop, J; Lin, KW
The coercivity and exchange bias field of ferro-/antiferromagnetic Co(90)Fe(10)/CoFe-oxide bilayers were studied as function of the surface morphology of the bottom CoFe-oxide layer. The CoFe-oxide surface structure was varied systematically by low energy (0-70 V) Argon ion-beam bombardment before subsequent deposition of the Co(90)Fe(10) layer. Transmission electron microscopy results showed that the bilayer consisted of hcp Co(90)Fe(10) and rock-salt CoFe-oxide. At low temperatures, enhanced coercivities and exchange bias fields with increasing ion-beam bombardment energy were observed, which are attributed to defects and uncompensated moments created near the CoFe-oxide surface in increasing amounts with larger ion-beam bombardment energies. Magnetometry results also showed an increasing divergence of the low field temperature dependent magnetization [Delta M(T)] between field-cooling and zero-field-cooling processes, and an increasing blocking temperature with increasing ion-beam bombardment energy. © 2012 IOP Publishing LTD.
Depth control of ferromagnetism in FePt3 films by ion-irradiation
(International Conference on Neutron Scattering, 2017-07-12) Causer, GL; Cortie, DL; Zhu, HL; Ionescu, M; Mankey, GJ; Klose, F
The roadmap which outlines storage technology of magnetic hard disk drives predicts storage densities above 5 Tb/in2 to be realised by isolated, individually addressable ferromagnetic (FM) bits of <10 nm in lateral dimension. In principle, artificially patterned structures of this type can be manufactured by x-ray, ion-and electron-beam lithography. However, there may be alternative solutions for obtaining these regular, nanoscale patterns of isolated FM dots. Our proposal is to locally transform a non-magnetic layer into a pattern of geometrically defined FM islands. Such a phase transition could be initiated by locally changing some physical parameter of the layer, such as its strain state or chemical composition leading to ferromagnetism. Here, we present a chemical order (paramagnetic) to chemical disorder (FM) phase transition stimulated by He+ irradiation of a FePt3 thin film. This talk will present preliminary work focussing on depth profiling the ion-beam induced FM order. By controlling the energy (15 keV) and fluence (2x1016 ions/cm2) of the ion-beam, we show ferromagnetism can be locally induced into the upper-half volume of the initially chemically well-ordered 280 nm FePt3 film. Polarised neutron reflectometry was used to investigate the depth dependence of the layer averaged ion-beam induced FM moment within the thin film. Data analysis of the Kiessig fringes observed in the reflectivity post-irradiation suggest the FM / nonmagnetic interface is atomically sharp. The resulting bilayer structure was found to be homogenous in chemical composition but heterogeneous in both chemical and magnetic orders.
Depth-profiling magnetic interfaces formed intrinsically in FePt3 by ion-beams
(American Physical Society, 2018-03-07) Causer, GL; Cortie, DL; Zhu, HL; Ionescu, M; Mankey, GJ; Wang, XL; Klose, F
Using ion-beams to locally modify material properties is rapidly gaining momentum as a technique of choice for the fabrication of magnetic nano-elements because the method provides the capability to nano-engineer in 3D, which is important for many future spintronic technologies. The precise definition of the resulting element shape is crucial for device functionality. In this work, the intrinsic sharpness of a magnetic interface formed by nano-machining FePt3 films using He+ irradiation is investigated. Through careful selection of the irradiating ion’s energy and fluence, ferromagnetism is locally induced into a fractional volume of a paramagnetic (PM) FePt3 film by modifying the chemical order parameter. Using a combination of magnetometry, transmission electron microscopy and polarised neutron reflectometry it is demonstrated that the interface over which the PM to ferromagnetic modulation occurs is confined to a few atomic monolayers only. Using density functional theory, the mechanism for the ion-beam induced magnetic transition is elucidated and shown to be caused by an intermixing of Fe and Pt atoms in anti-site defects above a threshold density.
The effect of single crystalline substrates and ion-beam bombardment on exchange bias in nanocrystalline NiO/Ni80Fe20 bilayers
(Institute of Electrical and Electronics Engineers (IEEE), 2013-12-23) Cortie, DL; Shueh, C; Lai, BC; Pong, PWT; van Lierop, J; Klose, F; Lin, KW
Methods to modify the magnetic coercivity and exchange bias field of nanocrystalline antiferromagnetic/ferromagnetic NiO/Ni 80 Fe 20 thin films were investigated for bilayers grown using ion-assisted deposition onto different single crystalline substrates. An enhanced coercivity was found at 298 K for the films deposited on single crystalline MgO (100) and Al 2 O 3 (11-20) substrates. After field cooling the films to 50 K, the NiO/NiFe bilayer grown on Al 2 O 3 (11-20) exhibited the largest exchange bias ( - 25 Oe). The second part of the study investigated ion-beam modification of the ferromagnetic surface prior to the deposition of the NiO layer. A range of ion-beam bombardment energies (V EH ) were used to modify in situ the NiFe surface during the deposition of NiO/NiFe/SiO 2 films. Cross-sectional transmission electron microscopy showed a systematic reduction in the thickness of the NiFe layers with increasing Ar + bombardment energies attributed to etching of the surface. In addition, the bombardment procedure modified the magnetic exchange bias of the composite structure in both the as-prepared and field-cooled state. © 2013 IEEE
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.
Enhancement of the magnetic interfacial exchange energy at a specific interface in NiFe/CoO/Co trilayer thin films via ion-beam modification
(AIP Scitation, 2014-01-01) Cortie, DL; Ting, YW; Chen, PS; Tan, X; Lin, KW; Klose, F
A series of ferromagnetic Ni 80Fe20(55 nm)/antiferromagnetic CoO (25 to 200 nm)/ferromagnetic Co (55 nm)/SiO2(substrate) trilayer thin films were fabricated by ion-beam assisted deposition in order to understand the role of ion beam modification on the interfacial and interlayer coupling. The microstructural study using transmission electron microscopy, X-ray reflectometry, and polarised neutron reflectometry showed that ion-beam modification during the deposition process led to an oxygen-rich Co/CoO nanocomposite interface region at the bottom layer. This interface caused a high exchange bias field for the ferromagnetic cobalt. However, the exchange bias for top permalloy ferromagnet remained low, in line with expectations from the literature for the typical interfacial energy. This suggest that the ion-beam enhancement of the magnetic exchange bias is localized to the Co/CoO interface where local microstructural effects provide the dominant mechanism. © 2020 AIP Publishing LLC
Evolution of the neutron-scattering capability on the OPAL reactor at ANSTO
(Taylor & Francis Online, 2016-04-29) Klose, F; Constantine, P; Kennedy, SJ; Schulz, JC; Robinson, RA; Holden, PJ; McIntyre, GJ
Australia is currently in the very privileged position of having the world's newest, fully operating research reactor, OPAL. As a consequence, the suite of neutron-beam instruments is also amongst the youngest and most advanced in the world, with full advantage taken in their construction of lessons learned at reactors elsewhere to develop state-of-the-art instruments that are best suited to the local and regional user communities. There are two thermal-neutron beam ports, two cold-neutron beam ports, and two (future) hot-neutron beam ports around the OPAL reactor core (see Fig. 3 in [1] and [2]). One each of the thermal-neutron and cold-neutron ports feed into a set of three guide bundles that serve the present (first) guide hall. In the initial construction phase, completed in 2007, only the outer two (TG1 and TG3) of the thermal guides, and the outer two (CG1 and CG3) of the cold guides were installed. The other thermal-neutron (TG4) and cold-neutron (CG4) guides are relatively short, to serve single instruments within the reactor beam hall with the highest flux but without eliminating line-of-sight [2]. Table 1 lists the current suite of instruments at the OPAL reactor, with brief technical details and the principal features. Figure 1 shows the layout of the current suite, with the anticipated location of the next instrument, BioRef (vide infra), indicated. We now briefly outline the evolution of the suite. © 2021 Informa UK Limited
Exchange 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, F
We 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.
Growth and properties of strain-tuned SrCoOx (25≤ x<3) thin films
(Australian Institute of Physics, 2016-02-05) Hu, S; Seidel, J; Klose, F
Controlling material properties by strain is one of the main concepts of thin film growth technology. By altering the order parameter in ferroic materials with which the lattice is coupled, new properties can be achieved, e.g. in perovskite SrCoOx which was identified as a parent phase of strong spin-phonon coupling materials. Here, we present results on a strain-induced antiferromagnetic-ferromagnetic phase transition in high quality epitaxial SrCoOx (2.5≤x<3) (oxygen deficient SrCoO3) thin films grown on (001) SrTiO3, (110) DyScO3 and (001) LaAlO3 substrates by pulsed laser deposition. Electronic and magnetic properties of the samples were characterized by XAS, XPS, neutron scattering and magnetometry measurements. Our results demonstrate that the ferromagnetism observed in SrCoOx/SrTiO3 can be suppressed and changed to antiferromagnetism in SrCoOx/DyScO3 through tensile strain. Further measurements on SrCoOx/LaAlO3 are currently on-going.
High magnetization FeCo/Pd multilayers
(American Vacuum Society, 2008-07) Walock, MJ; Ambaye, H; Chshiev, M; Klose, F; Butler, WH; Mankey, GJ
We have fabricated multilayer samples with varying superlattice periodicity and interlayer thicknesses to determine the nature of the enhanced moment in this intriguing thin film system. Magnetic characterization experiments show an enhanced magnetic moment in the multilayers as compared to a single layer film containing the same amount of FeCo. However, since the magnetization is defined as the magnetic moment divided by the sample volume, the sample exhibits an overall reduction in the magnetization when the volume of the Pd layers is also taken into account. Our experimental findings are also supported by theoretical calculations which identify the origin of the increased magnetic moment in the multilayer system. Polarized neutron reflectivity experiments will be used to determine the lateral distribution of the magnetization in a number of superlattice samples. © 2008, American Vacuum Society
Hydrogen-driven switching of the magnetic surface anisotropy at the Co/Pd interface
(American Physical Society, 2019-03-05) Causer, GL; Kostylev, M; Cortie, DL; Wang, XL; Klose, F
Heterostructures exhibiting perpendicular magnetic anisotropy (PMA) have proven to be indispensable within the magnetic recording industry. By exploiting the hydrogen-induced modifications to PMA which occur exclusively at the ferromagnetic/Pd interface, an opportunity exists to expand the potential applications of PMA-based heterostructures into the realm of hydrogen sensing using ferromagnetic resonance (FMR) - an electron-spin based technology. Here, we present an interface-resolved in-operando study of a Co/Pd film which features tailorable PMA in the presence of hydrogen gas. We combine polarized neutron reflectometry with in-situ FMR to explore the nanoscopic interactions of hydrogen at the Co/Pd interface which affects the spin-resonance condition during hydrogen cycling. Key experimental data and theoretical modelling reveal that the interfacial PMA of the Co/Pd film suppresses non-reversibly upon primary exposure to hydrogen gas – highlighting a potential avenue for spintronics-based hydrogen sensing.
In-situ polarized 3 He-based neutron polarization analyzer for SNS magnetism reflectometer
(Insitute of Physics, 2010-12-16) Lee, WT; Tong, X; Pierce, J; Fleenor, M; Ismaili, A; Robertson, JL; Chen, WC; Gentile, TR; Hailemariam, A; Goyette, R; Parizzi, A; Lauter, V; Klose, F; Kaiser, H; Lavelle, C; Baxter, DV; Jones, GL; Wexler, J; McCollum, L
We report here the construction and neutron transmission test results of an in-situ polarized 3 He-based neutron polarization analyzer system for the Magnetism Reflectometer at the Spallation Neutron Source, Oak Ridge National Laboratory. The analyzer uses the Spin-Exchange Optical Pumping method to polarize the 3 He nuclei of a cell of 3 He gas. Polarized neutrons scattered from the sample are intercepted by the polarized 3 He gas which strongly absorbs neutrons in one spin-state while allowing most neutrons in the other spin-state to pass through. To maintain a stable analyzing efficiency during an experiment, the 3 He gas is continuously polarized in - situ on the instrument. Neutron transmission measurements showed that 73% 3 He polarization was reached in this setup. © 2010, Insitute of Physics.
Intrinsic 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, F
Polarized 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.
Magnetic interface phenomena in nano-architectures and their applications
(Australian Institute of Nuclear Science and Engineering (AINSE), 2018-11-19) Causer, GL; Cortie, DL; Zhu, HL; Kostylev, M; Ionescu, M; Mankey, GJ; Wang, XL; Klose, F
Interfaces between heterostructure components in nanoscale films play important roles in communicating low-dimensional phenomena and act as anchor points for the direct control and tunability of device performance. In this talk I will give an overview of our group’s recent investigations into the occurrence of magnetic interface phenomena in low-dimensional thin-film systems which have conceivable utility in future condensed-matter technologies. First, the magnetic interface quality of an FePt3 nano-magnet formed via ion-induced chemical disorder will be analysed [1]. Here, neutron and electron measurements used in combination with density functional theory calculations reveal a rather counterintuitive result which could prove beneficial towards the development of ultra-high density magnetic recording devices. In a second study, the layer-averaged static magnetisation and macroscopic magneto-dynamic behaviours of a Co/Pd bilayer during hydrogen-gas cycling are analysed. To perform this characterisation, we first had to develop and commission an original sample environment which innovatively combines polarised neutron reflectometry and microwave spectroscopy [2]. The Co/Pd interface is found to feature tailorable magnetic surface anisotropy in the presence of hydrogen gas – the mechanism of which could act as a safety switch in next-generation vehicles powered by hydrogen.

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