Elastic Softening in HoFe2Al10

To investigate the 4f-electronic states under the crystal electric field (CEF) in HoFe2Al10, we carried out ultrasonic and specific heat measurements on single-crystalline samples. We found elastic softening of the transverse elastic modulus C55 below 20K and two Schottky peaks at 2 and 20K in the magnetic specific heat. By theoretical analyses of the modulus and the magnetic specific heat based on the CEF theory, we reproduced the elastic softening and the two Schottky peaks, and obtained the CEF parameters.