The temperature dependence of the magnetic viscosity coefficient (Sv), the activation volume (v), and the anisotropy field (HA) were examinedfor Sr-Na-Zn W-type hexagonal ferrite magnet from 77 to 623 K. Samples with different coercive forces (HcJ) were prepared, and the dependence of Sv and v on Hcj was studied at 300 K. The results show that the temperature dependence of Sv is the same as that ofHcj. The value of v is inversely proportional to HA. The logarithm of Sv is proportional to In

more »

... nd H~J is proportional to va.1, as in the case of SmzFel7Nx and SrM particles used in magnets and BaMfine particles used for high density recording media. They are considered to have a similar coercive force mechanism.