Temperature-dependent Eu spin reorientations in the tetragonal A-type antiferromagnet EuGa $ _4 $ induced by small ab-plane magnetic fields

摘要: The body-centered-tetragonal antiferromagnet EuGa exhibits A-type antiferromagnetic order below its N\'eel temperature K in magnetic field where the moments are ferromagnetically aligned in the -plane with the Eu moments in adjacent Eu planes aligned antiferromagnetically. Previous magnetization versus field measurements revealed that the moments exhibit a spin-reorientation transition at a critical field where the Eu moments become perpendicular to an in-plane magnetic field while still remaining in the plane. A theory for K was previously presented that successfully explained the observed low-field moment-reorientation behavior at K. Here we present a theory explaining the observed dependence of in the [1,0,0] direction for from 2 to 14 K arising from a -dependent anisotropy energy.