Spin reorientations in (Er/sub x/Y/sub 1-x/)/sub 2/Fe/sub 14/B and (Er/sub x/Pr/sub 1-x/)/sub 2/Fe/sub 14/B systems

The bulk magnetic properties of (Er/sub x/Y/sub 1-x/)/sub 2/Fe/sub 14/B and (Er/sub x/Pr/sub 1-x/)/sub 2/Fe/sub 14/B systems were studied over the temperature range 4.2 - 1100 K. Lattice parameters, saturation magnetizations, Curie temperatures and spin reorientation temperatures were determined. Theoretical description of the detailed magnetic behavior is presented, based on a crystal field model. The (Er/sub x/Y/sub 1-x/)/sub 2/Fe/sub 14/B compounds were all found to exhibit plane-to-axis spin reorientation similar to that observed for Er/sub 2/Fe/sub 14/B, with the transition temperature decreasing with increasing Y content. In contrast, the spin reorientations in the (Er/sub x/Pr/sub 1-x/)/sub 2/Fe/sub 14/B systems appear to be of the cone-to-axis type. Since higher order crystal field terms appear to be significant only in the cases of Nd/sup 3+/ and Ho/sup 3+/, the results are discussed in terms of a crystal field Hamiltonian involving only 2nd order terms. Using known values of the exchange field, Fe anisotropy and the ratios of the crystal field coefficients, the multi-ion crystal field problem was formulated in terms of a single adjustable parameter (B/sub 2//sup O/(f)). It is shown that 2nd order crystal field terms are capable, not only of explaining the conical anisotropy of the (Er/sub x/Pr/sub 1-x/)/sub 2/Fe/sub 14/B systems, but also the decrease in the Er moment upon passing through the spin reorientation (as has been observed for Er/sub 2/Fe/sub 14/B). The magnetic structure of Er/sub 1.5/Pr/sub 0.5/Fe/sub 14/B is also predicted