Microwave Giant Magnetoresistance and Ferromagnetic and Spin-Wave Resonances in (CoFe)/Cu Nanostructures
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ave Giant Magnetoresistance and Ferromagnetic and Spin-Wave Resonances in (CoFe)/Cu Nanostructures V. V. Ustinova,*, A. B. Rinkevicha,**, I. G. Vazheninab,***, and M. A. Milyaeva a
b
Institute of Metal Physics, Ural Division, Russian Academy of Sciences, Yekaterinburg, 620108 Russia Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] Received January 24, 2020; revised March 23, 2020; accepted March 23, 2020
Abstract—The microwave phenomena that occur in magnetic multilayer (CoFe)/Cu nanostructures, which have a giant magnetoresistance, are studied. The transmission of waves through a nanostructure is used to investigate the microwave giant magnetoresistance effect. The changes in the transmission coefficient at frequencies of 29–38 GHz are found to exceed the relative magnetoresistance, which distinguishes the system under study from the nanostructures studied earlier. Ferromagnetic and spin-wave resonances are used to study the angular dependences of the microwave absorption spectra of a multilayer (CoFe/Cu)n nanostructure. The following parameters are determined: the critical angle that determines the boundaries of the ranges of excitation of uniform and nonuniform spin modes, the type of boundary conditions describing the pinning of spins on the outer nanostructure surfaces, and the surface anisotropy and exchange interaction constants. DOI: 10.1134/S1063776120070171
1. INTRODUCTION Antiferromagnets and artificial structures with antiferromagnetic ordering have specific magnetic properties and, hence, are of deep interest. The works performed under the guidance of A.S. Borovik-Romanov (see, e.g., [1, 2]) are important for understanding the dynamic magnetic properties of antiferromagnets. He studied the antiferromagnetic resonance and spin waves in antiferromagnets and found that the spin waves in antiferromagnets obey a linear dispersion law; in addition, he comprehensively investigated the parametric excitation of spin waves. Among the artificial structures with antiferromagnetic ordering, the metallic nanostructures consisting of ferromagnetic and nonferromagnetic metal layers are of particular interest. In these nanostructures, ferromagnetic metal layers are coupled by exchange interaction and the magnetization in each layer is antiparallel to the magnetization in the neighboring layer. These nanostructures have the giant magnetoresistance (GMR) effect [3, 4], which is caused by the spin-dependent electron scattering by a ferromagnetic layer boundary. The interlayer exchange interaction has an oscillating character depending on the nonferromagnetic layer (spacer) thickness. The GMR effect was observed in such nanostructures at microwave frequencies (μGMR) [5]. The authors of [6, 7] proposed and substantiated a method of microwave passage through a
nanostructure as a convenient method to study μGMR. The state of the art in this field of research was comprehensively de
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