Anisotropy energy of C uMn spin glasses

Abstract

We have investigated the angular dependence of the anisotropy energy of a CuMn 4.7 at. % glass alloy at Tg by susceptibility and torque measurements. In our experiments the remanent magnetization σ↘ is initially along z↘ and is then rotated by an angle θ in the yz plane by a magnetic field. We measure the ac susceptibility along y↘ and the torque needed to prevent the sample from rotating as a function of θ. Our measurements show that the anisotropy energy is purely unidirectional (E_A=−K cos θ) as long as the spin system rotates bodily (θ≲40°). For larger values of θ we observe irreversible and time dependent effects which reveal rearrangements of the spins. Such rearrangements stabilize the states around θ=π and explain previous results on the anisotropy around π(apparent uniaxial anisotropy).