Spin reorientation and magnetohistory of DyFe_12-xNb_xcompounds

Abstract

Structural and magnetic properties, especially the magnetocrystalline anisotropy of DyFe12-xNbx compounds with x = 0.55-0.85, have been investigated. The easy magnetization directions at room temperature for all the compounds are along the c-axis. With decreasing temperature the magnetocrystalline anisotropy changes from easy axis to easy cone at Tsr2, then to easy plane at Tsr1. A spin phase diagram has been constructed for DyFe12-xNbx. The change of magnetocrystalline anisotropy was further investigated by the angular dependence of magnetization with respect to the magnetic field at various temperatures. The temperature dependence of the cone angle was determined for DyFe11.3Nb0.7. It is noteworthy that with increasing Nb content both Tsr1 and Tsr2 decrease monotonically while the Curie temperature is almost independent of Nb content. The cone angle increases monotonically with decreasing temperature from Tsr2 and discontinuously comes up to 90° at Tsr1. The temperature dependence of the cone angle can be quite well defined in terms of crystal field theory. In addition, an obvious magnetohistory effect was observed for all compounds at low temperature. The critical field of magnetohistory was found to be smaller than 0.5 T for DyFe11.3Nb0.7.

Anomalies in magnetoelastic properties of DyFe11.2Nb0.8 compound

“…Details of the fitting procedure are as described previously. 2,6 Similar to the behaviours reported for DyFe 11.4 Nb 0. 6 6 and ErFe 12Àx Nb x , 2 the overall shape of the spectrum changes with decreasing temperature as a result of the change in anisotropy.…”

“…2,6 Similar to the behaviours reported for DyFe 11.4 Nb 0. 6 6 and ErFe 12Àx Nb x , 2 the overall shape of the spectrum changes with decreasing temperature as a result of the change in anisotropy. The temperature dependences of the hyperfine parameters are shown in Figure 3 with the spin reorientation transition temperatures marked by arrows.…”

“…With increasing Nb content both T sr1 and T sr2 decrease monotonically but their Curie temperature T C remains independent of Nb content. 6 Similar behaviours were also observed in TbFe 12Àx Ti x systems 7 where the spin reorientation temperatures are very sensitive to the Ti concentration (dT sr /dx ¼ À380 K/Ti) but T C remain almost unchanged with variation in Ti content.…”

“…With further decrease in temperature the cone angle, h (between the easy magnetization direction and the four-fold axis [001]) increases smoothly to T sr1 and exhibits an abrupt change up to 90 . 6 Due to interaction of the anisotropic orbital electron cloud around the Dy 3þ magnetic ion with the crystal field of the lattice, the strong magnetostructural coupling 11 can be reflected by the appearance of anomalies in the thermal expansion coefficients as observed here for DyFe 11.2 Nb 0. 8 .…”

“…The temperature dependences of the hyperfine parameters are shown in Figure 3 with the spin reorientation transition temperatures marked by arrows. Based on the fact, the 8i sites are considered to provide the largest contribution to the overall 3d anisotropy, 6 for clarity only the hyperfine field and quadrupole shift of the 8i sites are shown in Figure 3, in addition to the average values of the hyperfine parameters (full lines). It can be discerned from the trends of the data (dashed lines) that both the hyperfine field and quadrupole shift of the 8i sites exhibit a change around T sr2 .…”