Tailoring exchange bias through chemical order in epitaxial FePt3 films

Saerbeck, Thomas; Zhu, Hanliang; Lott, D.; Lee, H.; LeClair, P.; Mankey, G. J.; Stampfl, A. P. J.; Klose, F.

doi:10.1063/1.4812761

Cited by 12 publications

(7 citation statements)

References 29 publications

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“…FexPt1-x alloys are well known for their unusually robust magnetic anisotropy properties arising from the strong conduction electron spin-orbit interaction with the Fe orbital moment [17,18], and also for the dependence of the magnetic state on the chemical order. For example, well-ordered Fe0.25Pt0.75 exhibits antiferromagnetism, while chemically disordered Fe0.25Pt0.75 is ferromagnetic [19,20]. Ferromagnetic FexPt1-x films also exhibit quite large anomalous Hall effects (AHE) [21][22][23], which suggests that FexPt1-x can be a promising material for the generation of spin currents by the extrinsic SHE.…”

mentioning

confidence: 99%

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1−x Alloys

Ralph

Buhrman

2018

Phys. Rev. Lett.

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Robust spin Hall effects (SHE) have recently been observed in nonmagnetic heavy metal systems with strong spin-orbit interactions. These SHE are either attributed to an intrinsic band-structure effect or to extrinsic spin-dependent scattering from impurities, namely, side jump or skew scattering. Here we report on an extraordinarily strong spin Hall effect, attributable to spin fluctuations, in ferromagnetic Fe_{x}Pt_{1-x} alloys near their Curie point, tunable with x. This results in a dampinglike spin-orbit torque being exerted on an adjacent ferromagnetic layer that is strongly temperature dependent in this transition region, with a peak value that indicates a lower bound 0.34±0.02 for the peak spin Hall ratio within the FePt. We also observe a pronounced peak in the effective spin-mixing conductance of the FM/FePt interface, and determine the spin diffusion length in these Fe_{x}Pt_{1-x} alloys. These results establish new opportunities for fundamental studies of spin dynamics and transport in ferromagnetic systems with strong spin fluctuations, and a new pathway for efficiently generating strong spin currents for applications.

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mentioning

confidence: 99%

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1−x Alloys

Ralph

Buhrman

2018

Phys. Rev. Lett.

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“…Polarised neutron reflectometry (PNR) measurements performed on the artificial FM/AF bilayer confirm the interface between the two magnetic orders of FePt 3 is very sharp (<5 nm) and free of any chemical modulation [23]. Despite an almost perfect interface, the unique EB characteristics of the ion-beam derived FM/AF bilayer are an order of magnitude less than previous reports on FePt 3 FM/AF films fabricated by modulating the substrate temperature during film growth [20,24]. In response, the main objective of this article is to enhance the magnetic coupling across the FM/AF interface of the ion-beam-designed FePt 3 bilayer via thermal annealing.…”

Section: Introductionmentioning

confidence: 61%

“…By analysing the integrated intensity ratio between the film's fundamental and superstructure x-ray diffraction Bragg peaks [29], it is calculated that 82% of the film's Fe + Pt basis atoms (on average) assume the chemically ordered L1 2 atomic arrangement. From previous investigations, such films are known to order antiferromagnetically below a Néel temperature of ≈160 K [24]. The prepared film was subsequently irradiated at 298 K on the LEII-Surface Engineering beamline of the SIRIUS Tandem Accelerator located at the Australian Nuclear Science and Technology Organisation (ANSTO).…”

Section: Sample Preparation and Characterisationmentioning

confidence: 99%

Tailoring exchange bias in ferro/antiferromagnetic FePt₃ bilayers created by He⁺ beams

Causer

Zhu

Ionescu

et al. 2018

J. Phys.: Condens. Matter

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We report on artificial exchange bias created in a continuous epitaxial FePt film by introducing chemical disorder using a He beam, which features tailorable exchange bias strength through post-irradiation annealing. By design, the ferromagnetic (FM)/antiferromagnetic (AF) heterostructure exhibits stratified degrees of chemical order; however, the chemical composition and stoichiometry are invariant throughout the film volume. This uniquely allows for a consideration purely of the magnetic exchange across the FM/AF interface without the added hindrance of structural boundary parameters which inherently affect exchange bias quality. Annealing at 840 K results in the strongest exchange biased system, which displays a cross-sectional morphology of fine (<10 nm) domain structure composed of both of chemically ordered and chemically disordered domains. A magnetic model developed from fitting the characteristic polarised neutron reflectometry spectral features reveals that dual interactions can be attributed to the observed exchange bias: magnetic coupling at the FM/AF interface and also between neighbouring FM (chemically disordered) and AF (chemically ordered) domains within the nominally FM layer. Our results indicate that exchange bias is hindered at interfaces which are both chemically and magnetically perfect, while annealing can be used to balance the volume proportions of interfacial FM and AF domains to enhance the magnetic interface roughness for customisable exchange bias in mono-stoichiometric FM/AF heterostructures crafted by ion beams.

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“…26 The value of S is comparable to those previously obtained by our group following the same optimized sample preparation conditions. 27,28 The out-of-plane lattice parameter (a) of the film was determined to be a = 3.89 ± 0.01 Å, which is consistent with the reported bulk (a = 3.87 Å) 14 and previous thin film values (a = 3.88 Å). 13,29 From XRD analysis, the average out-of-plane FePt 3 crystallite size was 620 Å (lower-bound approximation only), with a mosaic spread of 0.81°along the film epitaxial growth direction.…”

Section: ■ Conclusionmentioning

confidence: 99%

Direct Measurement of the Intrinsic Sharpness of Magnetic Interfaces Formed by Chemical Disorder Using a He⁺ Beam

Causer

Cortie

Zhu

et al. 2018

ACS Appl. Mater. Interfaces

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Using ion beams to locally modify material properties and subsequently drive magnetic phase transitions is rapidly gaining momentum as the technique of choice for the fabrication of magnetic nanoelements. This is because the method provides the capability to engineer in three dimensions on the nanometer length scale. This will be an important consideration for several emerging magnetic technologies (e.g., spintronic devices and racetrack and random-access memories) where device functionality will hinge on the spatial definition of the incorporated magnetic nanoelements. In this work, the fundamental sharpness of a magnetic interface formed by nanomachining FePt films using He irradiation is investigated. Through careful selection of the irradiating ion energy and fluence, room-temperature ferromagnetism is locally induced into a fractional volume of a paramagnetic (PM) FePt film by modifying the chemical order parameter. A combination of transmission electron microscopy, magnetometry, and polarized neutron reflectometry measurements demonstrates that the interface over which the PM-to-ferromagnetic modulation occurs in this model system is confined to a few atomic monolayers only, while the structural boundary transition is less well-defined. Using complementary 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 antisite defects above a threshold density.

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Tailoring exchange bias through chemical order in epitaxial FePt3 films

Cited by 12 publications

References 29 publications

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1−x Alloys

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1−x Alloys

Tailoring exchange bias in ferro/antiferromagnetic FePt₃ bilayers created by He⁺ beams

Direct Measurement of the Intrinsic Sharpness of Magnetic Interfaces Formed by Chemical Disorder Using a He⁺ Beam

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Tailoring exchange bias through chemical order in epitaxial FePt3 films

Cited by 12 publications

References 29 publications

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1−x Alloys

Strong Enhancement of the Spin Hall Effect by Spin Fluctuations near the Curie Point of FexPt1−x Alloys

Tailoring exchange bias in ferro/antiferromagnetic FePt3 bilayers created by He+ beams

Direct Measurement of the Intrinsic Sharpness of Magnetic Interfaces Formed by Chemical Disorder Using a He+ Beam

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Tailoring exchange bias in ferro/antiferromagnetic FePt₃ bilayers created by He⁺ beams

Direct Measurement of the Intrinsic Sharpness of Magnetic Interfaces Formed by Chemical Disorder Using a He⁺ Beam