Mössbauer-Effect Study of the Magnetic Structure of Single-Crystal Erbium

The magnetic structures of erbium metal have been investigated using the Mössbauer effect with single-crystal absorbers and a paramagnetic Ho${\mathrm{Al}}_2$ source. Measurements were performed between 4.2 and 80°K on two single crystals, one with the $c$ axis parallel and the other perpendicular to the $\gamma$-ray beam. At 4.2°K an analysis of the relative areas of the five resonance lines yields a value of (26±3)° for the semiapex angle of the ferromagnetic cone. No analysis was made on data from the intermediate-temperature region, because of the small effect. In the high-temperature region, a two-line spectrum was obtained at 55°K with the $c$ axis parallel to the beam. The data are best fitted by two Lorentzian lines, but an approximate fit can be achieved with a distribution of Lorentzian lines appropriate to a continuous sinusoidal distribution of hyperfine field values. At the Néel temperature of 80°K, a single-line spectrum was found with a full width at half-maximum of 0.34 cm/sec.