351 ISSN 1062-8738, Bulletin of the Russian Academy of Sciences: Physics, 2017, Vol. 81, No. 3, pp. 351–353. © Allerton Press, Inc., 2017. Original Russian Text © L.A. Chekanova, S.V. Komogortsev, E.A. Denisova, L.A. Kuzovnikova, I.V. Nemtsev, R.N. Yaroslavtsev, R.S. Iskhakov, 2017, published in Izvestiya Rossiiskoi Akademii Nauk, Seriya Fizicheskaya, 2017, Vol. 81, No. 3, pp. 380–382. Ferromagnetic Resonance Linewidth in Powders Consisting of Core–Shell Particles L. A. Chekanova a , S. V. Komogortsev a, *, E. A. Denisova a, b , L. A. Kuzovnikova c , I. V. Nemtsev a , R. N. Yaroslavtsev a, b , and R. S. Iskhakov a a Kirensky Institute of Physics, Siberian Branch, Russian Academy of Sciences, Krasnoyarsk, 660036 Russia b Siberian Federal University, Krasnoyarsk, 660041 Russia c Krasnoyarsk Institute of Railway Engineering, Irkutsk State Railway Transport Engineering University, Krasnoyarsk, 660036 Russia *e-mail: komogor@iph.krasn.ru AbstractThe dependence of the ferromagnetic resonance linewidth on the thickness of nonmagnetic shells in powders consisting of ferromagnetic core–nonferromagnetic shell composite particles is investigated. It is found that an increase in shell thickness reduces the ferromagnetic resonance linewidth by several times, down to values comparable to those for coatings with compositions similar to that of the particle’s core. The observed effect is assumed to result from suppression of the inhomogeneity of demagnetizing fields in a pow- der consisting of magnetic particles. DOI: 10.3103/S1062873817030091 INTRODUCTION The ferromagnetic resonance (FMR) linewidth for the powders consisting of 3d metal particles can be as high as several kilooersteds. For cubic phases in Fe-, Co-, and Ni-based alloys, this is not only much larger than the linewidth for single crystals, but also exceeds by many times the expected linewidth for polycrystal- line samples [1]. Dipole–dipole interaction between neighboring particles does substantially affect both the magnetization vector orientation and the work of magnetization of an individual particle. In addition, dipole–dipole interaction leads to particle agglomera- tion with the formation of clusters with different shapes and sizes. The effective magnetic field acting on a powder particle is largely determined by the demagnetizing field, which depends on the size and shape of a particle cluster and the position the particles inside it. The inhomogeneity of the local effective fields eventually leads to very great FMR linewidths. When measuring the resonance absorption of electro- magnetic waves in a powder, this inhomogeneity is hard to control, which sharply reduces the utility of FMR in studying magnetic powders. The structure of the mutual arrangement of particles in magnetic pow- ders is poorly understood and depends on many fac- tors, including the prehistory of different effects on a powder. It is therefore nearly impossible to theoreti- cally consider such inhomogeneities in FMR line- width precisely. In this work, we isolated magnetic particles of a powder using a nonmagnetic shell to weaken the dipole–dipole interaction between them to the level at which the influence of the effective field inhomogeneity in a particle ensemble is weaker than that of the inhomogeneity inside particles. The aim of this work was to establish the influence a particle shell has on FMR linewidth. EXPERIMENTAL We investigated two particle coating techniques: the chemical deposition of a nonmagnetic shell on particles of a magnetic powder poured into a solution (series A), and chemical deposition on particles of a magnetic powder prepared in a solution according to the homogeneous nucleation scenario (series B). The formation of clusters of individual particles can funda- mentally differ for the different sample coating tech- niques we used. To prepare samples of series А, we used a finished Co–P powder with a known mass, which was ground in a mortar, mixed in a solution to form a homoge- neous suspension, and then coated with a copper shell from a solution containing CuSO 4 (12 g/L), trilon B (25 g/L), formalin (25 mL/L), and NaOH (pH 12) via chemical deposition. Knowing the weight of the pow- der and the mass of blue copper in the solution, we cal- culated the ratio between the two phases. To prepare samples of series В, we first synthesized powder (Co(Р), CoNi(P), CoFe(Р), or Fe(Р)) from a solution containing NiSO 4 (5 g/L), CoSO 4 (25 g/L by the example of CoNi(P) particles), Na 3 C 6 H 5 O 7 (40 g/L), and NaH 2 PO 2 (200 g/L). When the reaction