Magnetic, thermal, and magnetocaloric properties of the holmium trialuminide HoAl3 with polytypic phases

We investigate the magnetic, thermal, and magnetocaloric properties of the intermetallic HoAl3 compounds with two different crystal structures. The room-temperature equilibrium trigonal phase HoAl3 undergoes an antiferromagnetic (AFM) transition at the Néel temperature TNtri= 9.8 K. The AFM order of the compound is strong against the magnetic field, so that inverse magnetocaloric effect (MCE) is found even under a magnetic field change of 0–50 kOe. The high-pressure cubic phase HoAl3, prepared by a rapid-solidification process, is antiferromagnetically ordered below TNcub= 15 K. Magnetic and specific heat measurements reveal that this long-range AFM state becomes unstable as the temperature drops and then is replaced by a magnetic glassy state below a spin freezing temperature Tf= 11 K. The successive changes in magnetic state result in complicated temperature and field dependence of the MCE at low temperatures.