| 1. |
- Kravets, Anatolii, et al.
(författare)
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Effect of nanostructure layout on spin pumping phenomena in antiferromagnet/nonmagnetic metal/ferromagnet multilayered stacks
- 2017
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Ingår i: AIP Advances. - : American Institute of Physics Inc.. - 2158-3226. ; 7:5
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Tidskriftsartikel (refereegranskat)abstract
- In this work we focus on magnetic relaxation in Mn80Ir20(12 nm)/Cu(6 nm)/Py(dF) antiferromagnet/Cu/ferromagnet (AFM/Cu/FM) multilayers with different thickness of the ferromagnetic permalloy layer. An effective FM-AFM interaction mediated via the conduction electrons in the nonmagnetic Cu spacer - the spin-pumping effect - is detected as an increase in the linewidth of the ferromagnetic resonance (FMR) spectra and a shift of the resonant magnetic field. We further find experimentally that the spin-pumping-induced contribution to the linewidth is inversely proportional to the thickness of the Py layer. We show that this thickness dependence likely originates from the dissipative dynamics of the free and localized spins in the AFM layer. The results obtained could be used for tailoring the dissipative properties of spintronic devices incorporating antiferromagnetic layers.
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| 2. |
- Polishchuk, Dmytr, et al.
(författare)
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Antiferromagnet-mediated interlayer exchange : Hybridization versus proximity effect
- 2023
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 107:22
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the interlayer coupling between two thin ferromagnetic (F) films mediated by an antiferromagnetic (AF) spacer in F∗/AF/F trilayers and show how it transitions between different regimes on changing the AF thickness. Employing layer-selective Kerr magnetometry and ferromagnetic-resonance techniques in a complementary manner enables us to distinguish between three functionally distinct regimes of such ferromagnetic interlayer coupling. The F layers are found to be individually and independently exchange-biased for thick FeMn spacers - the first regime of no interlayer F-F∗ coupling. F-F∗ coupling appears on decreasing the FeMn thickness below 9 nm. In this second regime found in structures with 6.0-9.0-nm-thick FeMn spacers, the interlayer coupling exists only in a finite temperature interval just below the effective Néel temperature of the spacer, which is due to magnon-mediated exchange through the thermally softened antiferromagnetic spacer, vanishing at lower temperatures. The third regime, with FeMn thinner than 4 nm, is characterized by a much stronger interlayer coupling in the entire temperature interval, which is attributed to a magnetic-proximity induced ferromagnetic exchange. These experimental results, spanning the key geometrical parameters and thermal regimes of the F∗/AF/F nanostructure, complemented by a comprehensive theoretical analysis, should broaden the understanding of the interlayer exchange in magnetic multilayers and potentially be useful for applications in spin thermionics.
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| 3. |
- Polishchuk, Dmytr, et al.
(författare)
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Ferromagnetic resonance in nanostructures with temperature-controlled interlayer interaction
- 2016
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Ingår i: Low temperature physics (Woodbury, N.Y., Print). - : American Institute of Physics (AIP). - 1063-777X .- 1090-6517. ; 42:9, s. 761-767
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Tidskriftsartikel (refereegranskat)abstract
- This study is a comprehensive analysis of a multilayer F-1/f(d)/F-2pin structure's magnetic resonance properties, wherein F-1 and F-2pin are the free and exchange-coupled strong magnetic layers, and f is the weakly magnetic layer with a Curie point in the room temperature region. Depending on the magnetic state of the spacer f (ferromagnetic or paramagnetic) the exchange interaction between the F-2 and F-2pin layers becomes a function of the temperature, which opens up opportunities for practical applications. The obtained results show that the interlayer exchange coupling can be enhanced by decreasing the thickness of the spacer d, or by lowering the temperature. Strengthening the exchange coupling leads to a stronger manifestation of unidirectional anisotropy in the ferromagnetic resonance layer F-1, as well as to a broadening of the resonance line that is atypical for thin films. The observed features are analyzed in the context of comparing the effects of two different natures: the influence of the spacer d and the influence of the temperature. Thus, the behavior of changes to the unidirectional anisotropy remains the same given variation of both the thickness of the spacer and the temperature. However the broadening of the magnetic resonance line is more sensitive to changes in the interlayer interaction caused by variation of d, and is less susceptible to changes caused by temperature.
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| 4. |
- Polishchuk, Dmytr, et al.
(författare)
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Ferromagnetic resonance in nanostructures with temperature controlled interlayer interaction
- 2016
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Ingår i: Fizika Nizkih Temperatur. - : Institute for Low Temperature Physics and Engineering. - 0132-6414 .- 1816-0328. ; 42:9, s. 972-980
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Tidskriftsartikel (refereegranskat)abstract
- The work carries out a comprehensive analysis of magnetic resonance properties of F1/f(d)/F2pin multilayers, where F1 and F2pin are soft and hard magnetic layers and f is a weakly magnetic spacer with the Curie Curie temperature in the vicinity of room temperature. Depending on the magnetic state of the spacer, ferromagnetic or paramagnetic, the exchange interaction between F1 and F2pin becomes a function of temperature which is attractive for a number of applications. Our results show that the interlayer exchange coupling can be enhanced either by decreasing the spacer thickness, d, or lowering temperature. Stronger exchange coupling results in stronger unidirectional anisotropy of the ferromagnetic resonance in F1, as well as in atypical for thin films broadening of the resonance line. The observed behavior was analyzed taking into account two effects of different character - variable spacer thickness d and variable temperature. It is shown that the changes in the unidirectional anisotropy of the FMR spectra have a similar dependence on d and temperature. On the contrary, the FMR line broadening due to magnetization relaxation in the system is significantly affected by the changes in the interlayer exchange interaction on varying d, and is only slightly affected by the changes in temperature.
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| 5. |
- Polishchuk, Dmytr, et al.
(författare)
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Giant magnetocaloric effect driven by indirect exchange in magnetic multilayers
- 2018
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Ingår i: Physical Review Materials. - : AMER PHYSICAL SOC. - 2475-9953. ; 2:11
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Tidskriftsartikel (refereegranskat)abstract
- Indirect exchange coupling in magnetic multilayers, also known as the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, is highly effective in controlling the interlayer alignment of the magnetization. This coupling is typically fixed at the stage of the multilayer fabrication and does not allow ex situ control needed for device applications. In addition to the orientational control, it is highly desirable to also control the magnitude of the intralayer magnetization, ideally, being able to switch it on/off by switching the relevant RKKY coupling. Here we demonstrate a magnetic multilayer material incorporating thermally and field-controlled RKKY exchange, focused on a dilute ferromagnetic alloy layer and driving it though its Curie transition. Such on/off magnetization switching of a thin ferromagnet, performed repeatedly and fully reproducibly within a low-field sweep, results in a giant magnetocaloric effect, with an estimated isothermal entropy change of Delta S approximate to -10 mJ cm(-3) K(-1 )under an external field of similar to 10 mT, which greatly exceeds the performance of the best rare-earth based materials used in the adiabatic-demagnetization refrigeration systems.
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| 6. |
- Polishchuk, Dmytr, et al.
(författare)
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Magnetic Hysteresis in Nanostructures with Thermally Controlled RKKY Coupling
- 2018
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Ingår i: Nanoscale Research Letters. - : Springer. - 1931-7573 .- 1556-276X. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Mechanisms of the recently demonstrated ex-situ thermal control of the indirect exchange coupling in magnetic multilayer are discussed for different designs of the spacer layer. Temperature-induced changes in the hysteresis of magnetization are shown to be associated with different types of competing interlayer exchange interactions. Theoretical analysis indicates that the measured step-like shape and hysteresis of the magnetization loops is due to local in-plane magnetic anisotropy of nano-crystallites within the strongly ferromagnetic films. Comparison of the experiment and theory is used to contrast the mechanisms of the magnetization switching based on the competition of (i) indirect (RKKY) and direct (non-RKKY) interlayer exchange interactions as well as (ii) indirect ferromagnetic and indirect antiferromagnetic (both of RKKY type) interlayer exchange. These results, detailing the rich magnetic phase space of the system, should help enable the practical use of RKKY for thermally switching the magnetization in magnetic multilayers.
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| 7. |
- Polishchuk, Dmytr, et al.
(författare)
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Thermal switching of indirect interlayer exchange in magnetic multilayers
- 2017
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Ingår i: Europhysics letters. - : Institute of Physics Publishing. - 0295-5075 .- 1286-4854. ; 118:3
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Tidskriftsartikel (refereegranskat)abstract
- We propose a magnetic multilayer layout, in which the indirect exchange coupling (IEC also known as RKKY) can be switched on and off by a slight change in temperature. We demonstrate such on/off IEC switching in a Fe/Cr/FeCr-based system and obtain thermal switching widths as small as 10-20 K, essentially in any desired temperature range, including at or just above room temperature. These results add a new dimension of tunable thermal control to IEC in magnetic nanostructures, highly technological in terms of available materials and operating physical regimes.
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| 8. |
- Polishchuk, Dmytr, et al.
(författare)
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Thermally induced antiferromagnetic exchange in magnetic multilayers
- 2017
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:10
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate sharp thermally induced switching between ferromagnetic and antiferromagnetic RKKY ( Ruderman-Kittel-Kasuya-Yosida) exchange in a spin-valve with the spacer incorporating a thin diluted ferromagnetic layer as the core. We illustrate the mechanism behind the effect as being due to a change in the effective thickness of the spacer induced by the Curie transition into its paramagnetic state. The ability to switch between ferromagnetic and antiferromagnetic states in a magnetic multilayer by a slight change in temperature may lead to new types of spin-thermoelectronic devices for use in such applications as memory or oscillators.
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| 9. |
- Tykhonenko-Polishchuk, Yuliya, et al.
(författare)
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Spin-dependent scattering and magnetic proximity effect in Ni-doped Co/Cu multilayers as a probe of atomic magnetism
- 2019
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 125:2
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the spin transport and ferromagnetic resonance properties of giant magnetoresistance (GMR) Co/Cu-Ni multilayers with variable levels of Ni doping in the Cu spacer. We present an experimental evidence for a magnetic-to-diamagnetic transition in the atomic magnetic moment of Ni in the Cu matrix for concentrations below 15 at. % Ni. As its concentration is increased, Ni atoms turn into spin scattering centers, which is manifested experimentally as a step-like change in the GMR of the multilayers. This behavior is observed in multilayers with gradient-doped Cu spacers, where only the inner region was doped with Ni. In the uniformly doped spacers, the GMR decreases monotonously with increasing Ni content, indicating that Ni atoms are magnetic and act as spin relaxation centers in the entire dopant-concentration range studied. We explain the difference in the observed GMR behavior due to a strong magnetic proximity effect in the uniform spacers, which is efficiently suppressed in the gradient spacers. The observed magnetic phase transition is fully supported by our detailed ab initio calculations, taking into consideration structural relaxation in the system as well as potential Ni clustering. Controlling the loss or gain of the atomic magnetism for a specific dopant can be a tool in probing and controlling spin relaxation in materials and devices for spin-valve and spin-torque based applications.
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| 10. |
- Borynskyi, Vladyslav, et al.
(författare)
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Spin-wave Resonance in Arrays of Nanoscale Synthetic-antiferromagnets
- 2022
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Ingår i: Proceedings of the 2022 IEEE 12th International Conference "Nanomaterials: Applications and Properties", NAP 2022. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- The study concerns dynamics of standing spin waves in arrays of sub-100 nm elliptic synthetic-antiferromagnet (SAF) nanodisks. We performed a detailed ferromagnetic resonance analysis in conjunction with micro magnetic modeling to find out several prominent traits of such systems. One broad line is shown to be the sole resonant response for a SAF of the considered sizes. We demonstrate that this mode is degenerated, and its excitation map resembles a superposition of in-center and edge-type oscillations. We also show how this hybrid excitation leads to almost twofold enhancement in the shape-induced anisotropy of the mode.
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