Dmytro M. Polishchuk

Institute of Magnetism · Department of Thin Films Physics

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 induc...

We investigate switching of magnetic tunnel junctions (MTJs) driven by the thermal effect of the transport current through the junctions. The switching occurs in a specially designed composite free layer, which acts as one of the MTJ electrodes, and is due to a current-driven ferro-to-paramagnetic Curie transition with the associated exchange decou...

We demonstrate the strong tunability of the spin-pumping contribution to magnetic damping in a thin-film ferromagnetic free layer interfacing with a synthetic ferrimagnet (SFM), acting as a spin sink, via a thin Cu spacer. The effect strongly depends on the magnetic state of the SFM, a trilayer structure composed of two Fe layers coupled via indire...

We report on the effect of cap layer material on the magnetic properties and aging of the Fe-NW (nanowire) arrays grown on oxidized vicinal Si (111) templates using atomic terrace low angle shadowing technique. We find that the Fe-NW arrays capped with metallic (Ag) layers do not show any sign of degradation with aging, whereas NW arrays capped wit...

У монографії викладені фізичні основи та сучасні теоретичні й експериментальні результати вивчення мікрохвильової магнітної та термоіндукованої динаміки у плівках та наноелементах синтетичних антиферомагнетиків (САФ). Викладено теорію феромагнітного резонансу та біжучих спінових хвиль у наноелементах та плівках САФ, відповідно; представлено особлив...

We present all-electrical operation of a FexCr1−x-based Curie switch at room temperature. More specifically, we study the current-induced thermally driven transition from ferromagnetic to antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect coupling in a Fe/Cr/Fe17.5Cr82.5/Cr/Fe multilayer. Magnetometry measurements at different temperat...

Using the method of SQUID magnetometry, the features of the antiferromagnet-ferromagnet thermomagnetic transition in arrays of the nanosized disks of Py/NiCu/Py synthetic antiferromagnets (SAFs) have been investigated. The effective interlayer interaction in individual SAFs “ferromagnet/diluted ferromagnet/ferromagnet” (F2/f/F1) changes from high-t...

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...

We present all-electrical operation of a Fe$_x$Cr$_{1-x}$-based Curie switch at room temperature. More specifically, we study the current-induced thermally-driven transition from ferromagnetic to antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect coupling in a Fe/Cr/Fe$_{17.5}$Cr$_{82.5}$/Cr/Fe multilayer. Magnetometry measurements at...

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 micromagnetic 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...

Ferromagnetic/antiferromagnetic bilayers are interfaced with normal metal/ferromagnetic bilayers to form F * /AF/N/F valves. The N-spacer thickness is chosen such that it mediates strong indirect exchange [Ruderman–Kittel–Kasuya–Yosida (RKKY)] between the outer ferromagnetic layers, which varies in strength/direction depending on the N thickness an...

We design and demonstrate a compact, robust, and simple to assemble and tune permanent magnet suitable for NMR relaxometry measurements of microfluidic flows. Soft-magnetic stainless-steel plates, incorporated inside the magnet airgap, are key for obtaining substantially improved and tunable field homogeneity. The design is scalable for different N...

We study magnetic multilayers, incorporating dilute ferromagnetic spacers between strongly-ferromagnetic layers exhibiting a proximity-enhanced magnetocaloric effect. Using magnetometry and direct measurements of the adiabatic temperature change based on a nanomembrane-calorimetry, we find that the magnetocaloric effect in the studied multilayer is...

We design and demonstrate a compact, robust and simple to assemble and tune permanent magnet suitable for NMR relaxometry measurements of microfluidic flows. Soft-magnetic stainless steel plates, incorporated inside the magnet airgap, are key for obtaining substantially improved and tunable field homogeneity. The design is scalable for different NM...

Ferromagnetic/antiferromagnetic bilayers are interfaced with normal metal/ferromagnetic bilayers to form F*/AF/N/F valves. The N-spacer thickness is chosen such that it mediates strong indirect exchange (RKKY) between the outer magnetic layers, which varies in strength/direction depending on the N thickness and in direction on switching F. The syst...

We study magnetic multilayers, incorporating dilute ferromagnetic spacers between strongly-ferromagnetic layers exhibiting a proximity-enhanced magnetocaloric effect. Using magnetometry and direct measurements of the adiabatic temperature change based on a nanomembrane-calorimetry, we find that the magnetocaloric effect in the studied multilayer is...

We investigate spin dynamics in nanodisk arrays of synthetic-antiferromagnets (SAF) made of Py/NiCu/Py trilayers, where the NiCu spacer undergoes a Curie transition at about 200 K. The observed ferromagnetic resonance spectra have three distinct resonance modes at room temperature, which are fully recreated in our micromagnetic simulations, showing...

The magnetocaloric effect in exchange-coupled synthetic-antiferromagnet multilayers is investigated experimentally and theoretically. We observe a temperature-controlled inversion of the effect, where the entropy increases on switching the individual ferromagnetic layers from anti-parallel to parallel alignment near their Curie point. Using a micro...

We investigate spin dynamics in nanodisc arrays of synthetic-antiferromagnets (SAF) made of Py/NiCu/Py trilayers, where the NiCu spacer undergoes a Curie transition at about 200 K. The observed ferromagnetic resonance spectra have three distinct resonance modes at room temperature, which are fully recreated in our micromagnetic simulations showing...

Exchange biasing in ferromagnet/antiferromagnet bilayers is known to enhance the material’s ferromagnetic resonance frequency and make it strongly angle dependent due to the unidirectional anisotropy induced at the interface. We observe a ten-fold enhancement in frequency and angle-independent ferromagnetic resonance in bilayers of Py/FeMn with ult...

We observe a strong thermally controlled magnon-mediated interlayer coupling of two ferromagnetic layers via an antiferromagnetic spacer in spin-valve type trilayers. The effect manifests itself as a coherent switching as well as collective resonant precession of the two ferromagnets, which can be controlled by varying temperature and the spacer th...

The magnetic properties of thin-film multilayers [Fe/Py]/FeMn/Py are investigated as a function of temperature and thickness of the antiferromagnetic FeMn spacer using SQUID magnetometry. The observed behavior differs substantially for the structures with 6 nm and 15 nm FeMn spacers. While the 15 nm FeMn structure exhibits exchange pinning of both...

The magnetic properties of thin-film multilayers [Fe/Py]/FeMn/Py are investigated as a function of temperature and thickness of the antiferromagnetic FeMn spacer using SQUID magnetometry. The observed behavior differs substantially for the structures with 6-nm and 15-nm FeMn spacers. While the 15-nm-FeMn structure exhibits exchange pinning of both...

We observe a strong thermally-controlled magnon-mediated interlayer coupling of two ferromagnetic layers via an antiferromagnetic spacer in spin-valve type trilayers. The effect manifests itself as a field-induced coherent switching of the two ferromagnets, which can be controlled by varying temperature and the spacer thickness. We explain the obse...

Magnetic properties of multilayered [Fe–Cr/Cr]×8 nanostructures with the interlayer exchange coupling of the antiferromagnetic type and without the interlayer coupling have been studied. The values of the saturation magnetization and the interlayer exchange coupling constant are shown to strongly depend on the thickness and non-magnetic dilution of...

Ferromagnetic resonance in multilayer metal nanostructures containing an antiferromagnetic layer of variable thickness is studied. The contribution to the linewidth of the ferromagnetic resonance that is caused by spin-pumping current dissipation in an exchange-coupled antiferromagnetic/ferromagnetic bilayer is determined. The dissipative processes...

We demonstrate a 20-fold enhancement in the strength of the Ruderman–Kittel–Kasuya–Yosida interlayer exchange in dilute-ferromagnet/normal-metal multilayers by incorporating ultrathin Fe layers at the interfaces. Additionally, the resulting increase in the interface magnetic polarization profoundly affects the finite-size effects, sharpening the Cu...

We demonstrate a 20-fold enhancement in the strength of the RKKY interlayer exchange in dilute-ferromagnet/normal-metal multilayers by incorporating ultrathin Fe layers at the interfaces. Additionally, the resulting increase in the interface magnetic polarization profoundly affects the finite-size effects, sharpening the Curie transition of the mul...

We observe and analyze tunable relaxation of a pure spin current by an antiferromagnet in spin valves. This is achieved by carefully controlling the angle between a resonantly excited ferromagnetic layer pumping the spin current and the Néel vector of the antiferromagnetic layer. The effect is observed as an angle-dependent spin-pumping contributio...

Resonance properties of nanocrystalline ribbons of Fe73Cu1Nb3Si16B7 alloy annealed with the use of an electric current under a tensile stress of 180 MPa have been studied within the ferromagnetic resonance method. Two kinds of ferromagnetic regions with different anisotropic behaviors that coexist in the alloy after the annealing are detected. One...

Ferromagnetic resonance (FMR) in exchange-coupled ferromagnet-antiferromagnet bilayers commonly shows only one resonance mode corresponding solely to the excitation of the ferromagnetic component. Here we report an observation of a simultaneous excitation of both the ferromagnetic and antiferromagnetic films in a Py/FeMn bilayer, observed as two co...

We observe and analyze tunable relaxation of a pure spin current by an antiferromagnet in spin-valves. This is achieved by carefully controlling the angle between a resonantly excited ferromagnetic layer pumping the spin current and the N\'eel vector of the antiferromagnetic layer. The effect is observed as an angle-dependent spin-pumping contribut...

Spin valves form a key building block in a wide range of spintronic concepts and devices from magnetoresistive read heads to spin-transfer-torque oscillators. We elucidate the dependence of the magnetic damping in the free layer on the angle its equilibrium magnetization makes with that in the fixed layer. The spin pumping-mediated damping is aniso...

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...

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 ad...

Spin-valves form a key building block in a wide range of spintronic concepts and devices from magnetoresistive read heads to spin-transfer-torque oscillators. We elucidate the dependence of the magnetic damping in the free layer on the angle its equilibrium magnetization makes with that in the fixed layer. The spin pumping-mediated damping is aniso...

We investigate the spin transport and ferromagnetic resonance properties of giant magnetoresistive (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 i...

Indirect exchange coupling in magnetic multilayers, also known as the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, is known to be 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 applica...

We demonstrate a strong tunability of the spin-pumping contribution to magnetic damping in a thin-film ferromagnetic free layer interfaced with a synthetic ferrimagnet (SFM), acting as a spin-sink, via a thin Cu-spacer. The effect strongly depends on the magnetic state of the SFM, a trilayer structure composed of two Fe layers coupled via indirect...

Two sets of core/shell magnetic nanoparticles, CoFe2O4/Fe3O4 and Fe3O4/CoFe2O4, with a fixed diameter of the core (~ 4.1 and ~ 6.3 nm for the former and latter sets, respectively) and thickness of shells up to 2.5 nm were synthesized from metal chlorides in a diethylene glycol solution. The nanoparticles were characterized by X-ray diffraction, tra...

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 an...

Magnetic nanoparticles constitute promising tools for addressing medical and health-related issues based on the possibility to obtain various kinds of responses triggered by safe remote stimuli. However, such richness can be detrimental if different performances are not adequately differentiated and controlled. The aim of this work is to understand...

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 and obtain thermal switching widths as small as 10-20 K, essentially in any desired temperature range...

Ferromagnetic resonance (FMR) in magnetic multilayers of type F1/f/F2, where two strongly ferromagnetic layers F1 and F2 are separated by a weakly magnetic spacer f with a compositional gradient along its thickness, is investigated. The method allows to detect the weak signal from the spacer in additional to the more pronounced and readily measured...

The work carries out the quantitative analysis of magnetic characteristics of ensembles of magnetic nanoparticles La0.6Sm0.1Sr0.3MnO3, measured at different temperatures. On the basis of performed analysis, field and temperature dependences of magnetic moment of the ensemble have been modeled. The calculations stress the governing role of the distr...

In this work we focus on magnetic relaxation in Mn$_{80}$Ir$_{20}$(12 nm)/ Cu(6 nm)/ Py($d_\mathrm{F}$) 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 --...

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 ex...

The ferromagnetic resonance (FMR) linewidth and its anisotropy in F1/f/F2/AF multilayers, where spacer f has a low Curie point compared to the strongly ferromagnetic F1 and F2, is investigated. The role of the interlayer exchange coupling in magnetization relaxation is determined experimentally by varying the thickness of the spacer. It is shown th...

In-plane magnetic anisotropy of (La,Na)MnO3//LaAlO3 thin film has been investigated in the temperature range from 100 K to a critical temperature of ferromagnetic-paramagnetic phase transition, TC 260 K, using an electron spin resonance technique. Low-temperature magnetic anisotropy of the film has been found to be a superposition of biaxial and un...

Ferromagnetic resonance properties of F1/f/F2/AF multilayers, where weakly ferromagnetic spacer f is sandwiched between strongly ferromagnetic layers F1 and F2, with F1 being magnetically soft and F2—magnetically hard due to exchange pinning to antiferromagnetic layer AF, are investigated. Spacer-mediated exchange coupling is shown to strongly affe...

Ferromagnetic resonance in planar arrays of iron nanowires (NW) covered with a layer of MgO is studied as a function of aging time. Planar arrays of iron NW are grown on stepped vicinal surfaces of oxidized Si (111) substrates by low-angle molecular beam epitaxy. The ferromagnetic resonance measurements reveal a perpendicular unidirectional anisotr...

Doped perovskite manganites La1-xAxMnO3 with alkaline (or alkaline-earth) ions A have received considerable attention due to their interesting magnetic, magnetoresistive, and microwave properties [1-3]. Such compounds are examples of materials with complex magnetic orderings which exist over wide temperature and concentration ranges [4-7]. However,...

We have studied by the electron-spin resonance (ESR) and static magnetic field techniques, the La2/3Ba1/3MnO3 perovskite, which was previously shown to exhibit a martensitic phase transformation in the vicinity of Ts∼200 K [Physical Review B 68, 054109 (2003)], leading to its structural phase-segregated state. Resonant absorptions reveal that in th...

We have studied the effect of composition and heat-treatment conditions on the structural and transport properties of La1 − x − y Ca x Na y MnO3 ± δ solid solutions. The materials obtained offer a magnetoresistance of about 48% in a magnetic field of 1.2 MA/m.