Magnetic properties of hard magnetic FePt prepared by cold deformation

The second-order anisotropy constant, K₁(T), in tetragonal L1₀ FePt is deduced from the analysis of the magnetization versus field curves, between 4.2 K and 700 K. K₁(T) varies approximately as expected for local moments in the classical limit. The temperature dependence of the coercive field H_c(T) is discussed with reference to the so-called micromagnetic and global models. The observed behavior suggests that coercivity is governed by passage-expansion or de-pinning. Dipolar interactions are shown to increase the coercive field, rather than reduce it, which is usually the case.