Ferromagnetic resonance in a system of magnetic films with different Curie temperatures
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DISORDER, AND PHASE TRANSITION IN CONDENSED SYSTEM
Ferromagnetic Resonance in a System of Magnetic Films with Different Curie Temperatures E. V. Skorokhodova*, E. S. Demidovb, S. N. Vdovicheva, and A. A. Fraermana** a
Institute of Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia b Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] **e-mail: [email protected] Received October 19, 2016
Abstract—The peculiarities of absorption of rf electromagnetic radiation (ferromagnetic resonance) in multilayer NiFe/Ni0.65Cu0.35(d)/CoFe structures in a wide temperature range are analyzed. It is shown that the type of interaction of the NiFe and CoFe ferromagnetic films via a “weak” ferromagnetic Ni0.65Cu0.35 interlayer changes from antiferromagnetic to ferromagnetic upon cooling and a decrease in interlayer thickness d. The detected temperature dependence of the interlayer interaction indicates the possibility of observation of a strong magnetocaloric effect in the structures under investigation. DOI: 10.1134/S1063776117030177
1. INTRODUCTION The contact between two ferromagnets with different Curie temperatures leads to a substantial rearrangement of the magnetization distribution in the contacting subsystems. In the general case, this rearrangement involves demagnetization of the “strong” ferromagnet with a higher Curie temperature and magnetization of the “weaker” ferromagnet with a lower Curie temperature. An analogous situation takes place if one of the contacting magnets is in the paramagnetic phase. This “magnetic proximity” effect was investigated experimentally and theoretically in a number of studies [1–4]. The systems consisting of two strong ferromagnets (F) separated by an interlayer of a weak ferromagnet (f) with a Curie temperature lower or higher than the sample temperature are of considerable interest. As the material for such an interlayer, solid solutions NixCu1 – x can be used, the Curie temperature of which can be controlled by varying concentration x of the solution [5, 6]. The interest in multilayer F/f /F structures is due to the possibility of designing microgenerators of microwave radiation on their basis [7], in which the mutual orientation of magnetic moments of ferromagnetic films substantially depends on temperature. High values of the efficiency of magnetic cooling for such systems were predicted theoretically in [8]. The exchange interaction at the interfaces between a paramagnetic films and ferromagnetic “banks” leads to a decrease in the magnetic moment of the paramagnetic film and
ferromagnets in the case of antiparallel orientation of their magnetic moments and, hence, to an increase in the entropy of the system as compared to that for the parallel orientation. The switching between the states with different entropies occurs owing to the switching of the mutual orientation of magnetic moments of ferromagnetic films. In fact, the distribution of the “exchange” fields acting on the paramagnetic film
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