TEMPERATURE DEPENDENCES OF MAGNETIZATION AND SPIN-WAVES IN MNP

The temperature dependence of the easy axis magnetization in the ferromagnetic phase of MnP is measured to an accuracy of ΔM/M< ±5 × 10-4 over a range from 4.2 K to 280 K. Instead of the usual T3/2 law, T ln T dependence holds up to about Tc/2. The following spin wave dispersion is expected to exsist at 0 K; along the a axis it is nearly constant up to qa = Q and increases very rapidly beyond Q. where Q is the screw propagation vector, while for perpendicular to the a axis it is quadratic in q⊥. At a finite temperature, the calculated two-magnon renormalization causes increase of the magnon energy near qa∼Q which induces an anomalous suppression for decrease of magnetization in MnP. The ferro-screw phase transition seems also to be due to this effect. © 1979, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.