Structure and magnetocaloric properties of the Fe-doped HoTiGe alloy

The structure and magnetocaloric properties of the Fe-doped HoTiGe compound were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy, x-ray diffraction, magnetometry, and calorimetry. As with the early studies on the undoped compound, the Fe-containing alloy exhibited an antiferromagnetic-to-paramagnetic transition and a magnetocaloric effect peak at 90 K. The magnetization (M) versus temperature (T) data showed peaks at 10 and 90 K, while M versus field (H) curves showed the presence of a field-induced transition for all T<120 K; additionally, for all T<60 K, open hysteresis loops at the magnetic transitions were observed. XRD measurements between 10 and 60 K under various magnetic fields up to 3184 kAm (40 kOe) showed that the hysteresis was not accompanied by any change in crystallography. The magnetization derived entropy change -Δ Sm vs T plot also showed the presence of two peaks, at 20 and 90 K; but below 15 K, -Δ Sm increased steeply with decreasing temperature. It is believed that the minor phases in the Fe-doped alloy give rise to the magnetization-derived -Δ Sm peak at 20 K. The heat-capacity-derived -Δ Sm vs T plot for the Fe-doped alloy also showed the presence of two peaks at 20 and 90 K. However, the heat-capacity-derived -Δ Sm did not show a rapid rise with decreasing temperature below 15 K.