Mössbauer study of spin reorientation in Y_1.8Er _0.2Fe₁₄B

Fe⁵⁷ Mössbauer spectra were taken from 300 K down to 4.2 K for two single-crystal samples of Y_1.8Er _0.2Fe₁₄B, one cut with its [001] axis normal to the surface, the other with its diagonal of [100], [010], and [001] axes normal to the surface. The former sample has shown that the angle between the Fe spin and the [001] increases continuously below ∼90 K. This qualitatively agrees with the spin reorientation (i.e., the easy axis of magnetization rotates away from the [001] toward [100] on cooling below ∼90 K) which have already been observed by torque magnetometry. The latter sample has shown that the Fe spin actually rotates continuously; abrupt change of Fe spin direction, which have been already suggested to occur in Er₂Fe₁₄B, does not occur in Y_1.8Er_0.2Fe₁₄B. The samples were so thick that the intensity of strong absorption lines were saturated. We have derived a formula with which the saturation effect can be corrected in order to determine the angle of the Fe spin direction correctly.