Correlated spin glass: A new way to extremely soft magnetic materials

We consider amorphous solids with ferromagnetic exchange and small random anisotropy. In the absence of an applied field or coherent anisotropy these solids are characterized by zero net magnetization and smooth stochastic rotation of the local magnetization. The ferromagnetic correlation length R is large compared with the random anisotropy correlation length r: where . Krand A are the random anisotropy and exchange energies. This soft amorphous state should have a large zero field susceptibility , a low spin resonance frequency, , and should show a square root magnetization law, (Mo-M(H))∼ H^-1/2for a wide range of applied fields. Coherent anisotropy transforms the randomly ordered state into one with ferromagnetic domains and reduces the susceptibility.