The (x, T) magnetic phase diagram of Y2Co17−xCrx (1.17 ≤ x ≤ 3) compounds by neutron diffraction

We present the (x, T) phase diagram of the ferromagnetic Y2Co17−xCrx (x = 1.17, 1.76, 2.34, 3) compounds with rhombohedral structure (space group R3¯m, Th2Zn17-type), determined for the entire magnetically ordered regime from high-resolution neutron-diffraction data. Substitution of small amounts of Cr for Co was found to have drastic effects on the magnetic properties such as a decrease of the Curie (TC) and spin reorientation (TSR) temperatures as well as a decrease of the ordered-moment values. These effects could be brought into connection to the fact that Cr was found to have a preference for the four Co sites in the following order 6c > 18f > 9d > 18h. The number of Cr atoms found occupying the latter two sites, however, is within experimental error negligible. The magnetic phase diagram comprises three distinct regions of magnetic order in addition to the paramagnetic state: (a) the HT range (easy axis), (b) the LT (easy plane) for 0 < x < 2.3 and (c) the LT (canted) for 2.3 < x ≤ 3. Alloying with Cr promotes the easy-axis anisotropy at the cost of decreasing values of TC and TSR. It also leads to the formation of varying portions of the hexagonal Th2Ni17-modification (with similar magnetic properties) in samples with x ≥ 1.76. The crystal and magnetic structure of both modifications were refined simultaneously.