Magnetization and magnetoacoustics of single-crystalline ErFe5Al7 in high magnetic fields

Abstract

The magnetization and sound propagation in single-crystalline ErFe5Al7 (tetragonal crystal structure) have been studied in steady (up to 18T) and pulsed magnetic fields (up to 60T). The compound orders ferrimagnetically at a Curie temperature TC=201K and has a compensation point at Tcomp=34K. ErFe5Al7 displays a strong magnetic easy-plane anisotropy. A strong magnetic anisotropy is present as well within the basal plane; the [100] axis is the easy magnetization direction with a spontaneous magnetic moment Ms=1.3µB/f.u. at 2K. Field-induced magnetic transitions, two along the [100] axis and two along the [110] axis, have been found in the vicinity of T=Tcomp. Changes in the magnetic state at the transitions result in significant alterations of the spin–phonon coupling, which is manifested by sharp anomalies in the sound velocity and sound attenuation. Along the easy [100] axis the forced ferromagnetic state is reached in a field of about 50 T at 2K, whereas along the [110] direction saturation is expected only above 60T. A magnetic field-temperature phase diagram has been extracted up to 60T. From the experimental data a value of nErFe=3.3T/µB for the inter-sublattice Er–Fe exchange interaction has been obtained.