Disorder-driven critical behavior of complex susceptibility in an amorphous ferromagnet

The disorder-driven critical, multicritical, and phase coexistence characteristics of the complex magnetic susceptibility for the Blume-Capel model with a uniaxial anisotropy term that fluctuates in magnitude are analyzed within the framework of the linear response theory. The generalized flux conjugate to its generalized force is formulated as the time derivative of the magnetization. The stationary solution of the kinetic equation in a sinusoidal external magnetic field yields the magnetic dispersion and absorption factors χ1(ω), χ2(ω). The thermal behavior of ac susceptibility is examined thoroughly, focusing on the temperature dependencies of magnetic dispersion and absorption factors near first, second-order, and tricritical points. Crystal field variances of χ1(ω) and χ2(ω) are shown in the neighborhood of two successive first-order transitions between ordered and disordered critical points, where phase transitions occur between ordered and partly ordered phases.