Noncollinear Magnetic Order in a Dysprosium Layer and Magnetotransport Properties of a Spin Valve Containing the CoFe/Dy
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TRICAL AND MAGNETIC PROPERTIES
Noncollinear Magnetic Order in a Dysprosium Layer and Magnetotransport Properties of a Spin Valve Containing the CoFe/Dy/CoFe Structure R. S. Zavornitsyna, *, L. I. Naumovaa, M. A. Milyaeva, M. V. Makarovaa, b, T. P. Krinitsinaa, V. V. Proglyadoa, and V. V. Ustinova a
Mikheev Institute of Metal Physics, Ural Branch, Russian Academy of Sciences, Ekaterinburg, 620108 Russia Ural Federal University Named after the First President of Russia B.N. Yeltsin, Institute of Natural Sciences and Mathematics, Ekaterinburg, 620002 Russia *e-mail: [email protected]
b
Received February 12, 2020; revised March 3, 2020; accepted March 10, 2020
Abstract—Spin valves comprising a synthetic antiferromagnet and a CoFe/Dy/CoFe structure in the pinned layer were prepared by magnetron sputtering. It is shown that the Dy layer is characterized by crystallites, the [0002] direction of which is perpendicular to the film plane; a part of nanostructure, in which the spin-dependent electron scattering occurs, is characterized by smooth interfaces. Variations of magnetotransport properties of the spin valve, which are due to the formation of antiferromagnetic order in the dysprosium layer, are observed. Peculiarities of noncollinear magnetic order of the Dy layer were found to depend on the direction of magnetic moments of adjacent layers and magnetic field strength when passing through the Néel temperature. Keywords: dysprosium, spin valve, magnetoresistance, spin-flop state, helical order DOI: 10.1134/S0031918X20070121
INTRODUCTION The dysprosium rare-earth metal exhibits three temperature ranges of magnetic order. Below the Curie temperature (TC) dysprosium is a ferromagnet. In the temperature range TC–TN, where TN is the Néel temperature, dysprosium is characterized by an antiferromagnetic helical structure (helical phase); above TN, dysprosium becomes paramagnet. For bulk dysprosium, TC = 85 K and TN = 179 K [1]. The Néel temperature of dysprosium layer constituting a nanostructure depends on the layer thickness [2]. Dysprosium has a hexagonal close-packed (hcp) structure. In the case of a helical phase, the resulting moment of each basal plane makes some angle α0 with the magnetic moment direction of a neighboring basal plane. In the temperature range TC–TN, the α0 angle varies from 26.5 to 43.2° [3]; the helicoid step decreases from 40 to 25 Å [4]. The magnetic field affects the helical structure [1, 5]. In a critical field Нcr, the helical order breaks and transfers into a fan pseudo-ferromagnetic structure. The maximum value of Нcr reaches 11 kOe. It is already known [6] that in multilayered structures, the diffusion and formation of amorphous compounds occur at the rare-earth–transition metal
boundary; the TC temperature of the amorphous compounds is in a range of 300–500 K and the coercive force is temperature-dependent [7–9]. Two ferromagnetic layers in a “spin-valve” nanostructure are separated by a copper layer. The ferromagnetic layer referred to as the pinned layer is exchange coupled with
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