Double-spiral magnetic structure of the Fe/Cr multilayer revealed by nuclear resonance scattering

We have studied the magnetization depth profiles in a [57Fe(dFe)/Cr(dCr)]x30 multilayer with ultrathin Fe layers and nominal thickness of the chromium spacers dCr 2.0 nm using nuclear resonance scattering of synchrotron radiation. The presence of a broad pure-magnetic half-order (1/2) Bragg reflection has been detected at zero external field. The joint fit of the reflectivity curves and Mossbauer spectra of reflectivity measured near the critical angle and at the "magnetic" peak reveals that the magnetic structure of the multilayer is formed by two spirals, one in the odd and another one in the even iron layers, with the opposite signs of rotation. The double-spiral structure starts from the surface with the almost antiferromagnetic alignment of the adjacent Fe layers. The rotation of the two spirals leads to nearly ferromagnetic alignment of the two magnetic subsystems at some depth, where the sudden turn of the magnetic vectors by ~180 deg (spin-flop) appears, and both spirals start to rotate in opposite directions. The observation of this unusual double-spiral magnetic structure suggests that the unique properties of giant magneto-resistance devices can be further tailored using ultrathin magnetic layers.Comment: 9 pages, 3 figure

Highly Sensitive CoFeNi/Cu Superlattices with Magnetic Flux Concentrators

In the course of the work, it was possible to reduce the saturation fields of CoFeNi/Cu superlattices with the effect of giant magnetoresistance by a factor of 11 to 15–20 Oe using magnetic flux concentrators made of NiFeCuMo and NiFe materials.Работа выполнена в рамках государственного задания МИНОБРНАУКИ России по темам «Спин» АААА-А18-118020290104-2 и «Магнит» 122021000034-9 при частичной поддержке РФФИ (грант № 20-42-660018)

Magnetoresistive properties of exchange biased spin valve caused by helical magnetic ordering in dysprosium layer

Spin valves containing CoFe/Dy/CoFe nanostructure as a pinned layer were prepared by magnetron sputtering. Investigations of microstructure and magnetoresistive properties were performed. The magnetoresistive properties of the spin valve were used as the instrument to study the changes in magnetic state of the dysprosium layer. The existence of noncollinear magnetic ordering in dysprosium polycrystalline nanolayer was observed. The angle between the magnetic moments in a top and bottom part of the dysprosium layer was estimated. © Published under licence by IOP Publishing Ltd

PREDICTION OF MAGNETOTRANSPORT PROPERTIES OF SUPERLATTICES BASED ON MACHINE LEARNING METHODS

In the course of this work, a regression machine learning model was constructed based on a set of experimental data capable of predicting the magnetotransport properties of CoFeNi/Cu and CoFeNi/CuIn superlattices.Работа выполнена в рамках государственного задания МИНОБРНАУКИ России по темам «Спин» 122021000036-3 и «Магнит» 122021000034-9

Bending Deformation and Magnetoelastic Properties of a Spin Valve on a Polymer Substrate

We report the results of a study of bending deformation of spin valves sputtered on polyimide substrate. It was taken into account that two factors contribute to the change in the magnetoresistance. We have obtained the dependence of the magnetoelastic anisotropy constant on substrate elongation.Работа выполнена в рамках государственного задания МИНОБРНАУКИ России по темам “Спин” АААА-А18-118020290104-2 и «Магнит» №122021000034-9 при поддержке РФФИ (грант 20-42-660018 р_а)

Spin valve based sensor elements for full Wheatstone bridge

Present work deals with methods for creating opposite pinning directions in micro-objects based on a spin valve by one thermomagnetic treatment. The methods are based on the thermomagnetic treatment in spin-flop state of synthetic antiferromagnet. We use splitting the magnetic structure in spin-flop state of synthetic antiferromagnet to form opposite pinning directions in different micro-objects by one thermomagnetic treatment. The positive characteristic (dR/dH) was obtained in the two sensor elements of the full Wheatstone bridge, and the negative characteristic (dR/dH) in the other two elements. © Published under licence by IOP Publishing Ltd.Russian Foundation for Basic Research, RFBR: 19-02-0005718-10-2-37The research was carried out within the state assignment of Minobrnauki of Russia (theme “Alloys” АААА-А19-119070890020-3 and “Magnet” АААА-А18-118020290129-5), supported in part by RFBR (project No. 19-02-00057) and UD RAS (No. 18-10-2-37)

Shape Anisotropy Effect in Microstriped Spin Valves with Synthetic Antiferromagnet

Shape anisotropy effect on the field dependences of magnetoresistance for microstriped spin valves is investigated. Strong shape anisotropy effect on spin valve magnetic reversal and direction of magnetic moments of free and reference layers in the weak magnetic fields were revealed.Работа выполнена в рамках государственного задания по теме “Спин” АААА-А18-118020290104-2 и при поддержке РФФИ (грант 20-42-660018 р_а) и государственного задания МИНОБРНАУКИ России по теме «Магнит» №122022100034-9

Microstructure and magnetoresistance of Co90Fe10/Cu and Co65Fe26Ni9/Cu multilayers

Investigations of the microstructure, magnetic and magnetotransport properties of the optimized [Co90Fe10/Cu]n and [Co65Fe26Ni9/Cu] n multilayers with n = 32 prepared by magnetron sputtering are performed. These nanostructures exhibit the magnetoresistance values 83 % and 36 % at room temperature, respectively. The article presents the results of the influence of Co65Fe26Ni9 alloy on the magnetoresistance values and crystal structure of multilayers. In the periodic part of the nanostructure [Co65Fe26Ni9/Cu] n based on CoFeNi ternary alloy, besides fcc the formation of a bcc phase in the continuous boundaries around crystallites is found. © Published under licence by IOP Publishing Ltd

Structure and magnetic properties of the Co2FeAl and Co2NiSi Heusler alloy films

The structural and magnetic properties (field dependences of the magnetization in magnetic fields of up to 6 kOe) of thin-film Co2FeAl, and Co2NiSi Heusler alloys grown by pulsed laser deposition on glass and a single-crystalline Al2O3 R-plane substrate at different growth temperatures (20, 280 and 420 °C) were studied. It was found that the stoichiometric composition of the films depends on the substrate temperature during growth and repeats the composition of the target for films grown at low temperatures. The films deposited on a single crystalline Al2O3 substrate have uniaxial magnetic anisotropy in the plane. © Published under licence by IOP Publishing Ltd.This work was partly supported by the state assignment of Minobrnauki of Russia (themes “Spin” No. АААА-А18-118020290104-2), RFBR grants (Nos. 18-32-00686 and 18-02-00739) and the Government of the Russian Federation (state contract No. 02.A03.21.0006)

Tunable Spin-Flop Transition in Artificial Ferrimagnets

Spin-flop transition (SFT) consists in a jump-like reversal of antiferromagnetic (AF) lattice into a noncollinear state when the magnetic field increases above the critical value. Potentially the SFT can be utilized in many applications of a rapidly developing AF spintronics. However, the difficulty of using them in conventional antiferromagnets lies in (a) too large switching magnetic fields (b) the need for presence of a magnetic anisotropy, and (c) requirement to apply magnetic field along the correspondent anisotropy axis. In this work we propose to use artificial ferrimagnets (FEMs) in which the SFT occurs without anisotropy and the transition field can be lowered by adjusting exchange coupling in the structure. This is proved by experiment on artificial Fe-Gd FEMs where usage of Pd spacers allowed us to suppress the transition field by two orders of magnitude. © 2021 authors. Published by the American Physical Society. Open access publication funded by the Max Planck Society.We thank A. B. Drovosekov, D. I. Kholin, and D. Cortie for fruitful discussion of the results. This work is partially based on experiments performed at the NREX instrument operated by the Max Planck Society at the MLZ, Garching, Germany and supported by the Deutsche Forschungsgemeinschaft (Project No. 107745057-TRR80). Research in Ekaterinburg was performed within the state assignment of Minobrnauki of Russia (theme “Spin” No. AAAA-A18-118020290104-2) and was partly supported by Russian Foundation for Basic Research (Project No. 19-02-00674)