Development of nanostructured magnetic materials based on high-purity rare-earth metals and study of their fundamental characteristics

The effect of the structural state on magnetic and hysteretic properties of compounds with high contents of a 3$d$ transition metal, i.e., $R_2$Fe$_{14-x}$Co$_x$B and $R$Fe$_{11-x}$Co$_x$Ti (where $R$ = Y, Sm; 0 $\le x\le$ 8), was studied. Alloys were prepared using high-purity rare-earth metals by two different methods: induction melting and argon-arc melting. Severe plastic deformation and rapid melt-quenching allowed preparation of nanostructured samples. Structural studies of the samples were performed by X-ray powder diffraction and atomic-force microscopy methods. Magnetic hysteretic properties were studied using a PPMS magnetometer in the temperature range of 4.2–300 K in fields to 20 kOe. It was shown that the dependences of fundamental magnetic parameters (Curie temperature, saturation magnetization, and magnetocrystalline anisotropy constant) on the cobalt content exhibit a similarity for both systems. It was found that, depending on sample treatment, the grain size varies from 30 to 70 nm after severe plastic deformation and in wider ranges (from 10 to 100 nm) after rapid quenching, not exceeding the single-domain size. The interrelation between the microstructure and magnetic characteristics was investigated. It was revealed that the concentration dependence of the coercivity for both systems has a maximum at the same cobalt content, i.e., $x$ = 2.