Magnetic, thermal, and magnetocaloric properties of the holmium trialuminide HoAl$_{3}$ with polytypic phases

We investigate the magnetic, thermal, and magnetocaloric properties of the intermetallic HoAl$_{3}$ compounds with two different crystal structures. The room-temperature equilibrium trigonal phase HoAl$_{3}$ undergoes an antiferromagnetic (AFM) transition at the Neel temperature $T^{\rm tri}_{\rm N} =$ 9.8 K. The AFM ordering 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 $T^{\rm cub}_{\rm N} =$ 15 K. Magnetic and specific heat measurements reveal that this long-range AFM state becomes unstable as the temperature drops and then it is replaced by a magnetic glassy state below a spin freezing temperature $T_{\rm f} =$ 11 K. The successive changes in magnetic state result in complicated temperature and field dependence of the MCE at low temperatures.