Anisotropic magnetic properties and giant magnetocaloric effect of single-crystal PrSi

A single crystal of PrSi was grown by the Czochralski method in a tetra-arc furnace. Powder x-ray diffraction of the as-grown crystal revealed that PrSi crystallizes in an FeB-type structure with space group Pnma (No. 62). The anisotropic magnetic properties were investigated by means of magnetic susceptibility, isothermal magnetization, electrical transport, and heat capacity measurements. Magnetic susceptibility data clearly indicate the ferromagnetic transition in PrSi with a $T_C$ of 52 K. The relative easy axis of magnetization was found to be the [010] direction. Heat capacity data confirm the bulk nature of the transition at 52 K and exhibit a huge anomaly at the transition. A sharp rise in the low-temperature heat capacity has been observed (below 5 K) which is attributed to the ${}^{141}$Pr nuclear Schottky heat capacity arising from the hyperfine field of the Pr moment. The estimated Pr magnetic moment 2.88 ${\mu }_{\mathrm{B}}$/Pr from the hyperfine splitting is in agreement with the saturation magnetization value obtained from the magnetization data measured at 2 K. From the crystal electric field analysis of the magnetic susceptibility, magnetization, and heat capacity data it is found that the degenerate $J=4$ Hund's rule derived state of the Pr${}^{3+}$ ion splits into nine singlets with an overall splitting of 284 K, the first excited singlet state separated by just 9 K from the ground state. The magnetic ordering in PrGe appears to be due to the exchange-generated admixture of low-lying crystal field levels. The magnetocaloric effect (MCE) has been investigated from magnetization data along all three principal crystallographic directions. The large magnetic entropy change, $-\Delta S_M=$22.2 J/kg K, and the relative cooling power, RCP = 460 J/kg, characteristic of the giant magnetocaloric effect are achieved near the transition temperature ($T_C$ = 52 K) for $H=$ 70 kOe along $\left[010\right]$. Furthermore, the PrSi single crystal exhibits a giant MCE anisotropy.

Figure 1

Powder x-ray diffraction pattern of PrSi along with the Rietveld refinement. A representative Laue pattern, corresponding to the (010) plane, is shown in the inset.

Figure 2

Temperature dependence of electrical resistivity of PrSi. The inset shows the low-temperature part of the electrical resistivity. The solid lines are the fits to the spin-wave gap model.

Figure 3

(a) Temperature dependence of magnetization of PrSi along [100], [001], and [010] in an applied field of 1 kOe plotted on a log-log scale. Panel (b) shows the reciprocal magnetic susceptibility of PrSi. The solid lines represent the Curie-Weiss fit as mentioned in the text.

Figure 4

Inverse $\chi$ vs $T$ plot. The solid lines show the fit based on the crystalline electric field model (see text for details). The crystal field energy levels are shown.

Figure 5

Isothermal magnetization of PrSi along the three principal crystallographic directions. The upper inset shows calculated magnetization based on the crystal field model and the lower inset shows the Arrott plot.

Figure 6

Temperature dependence of the specific-heat capacity of LaSi. The dashed line and the continuous line are fits to the Debye model and Debye+Einstein model (see text for details). The inset shows the low-temperature part of $C/T$ versus $T^2$ plot. The solid line in the inset is the fit to the $C/T=\gamma +\beta T^2$ expression.

Figure 7

(a) Heat capacity of PrSi and LaSi, and the magnetic part of the heat capacity. The top inset shows $C_{4\mathrm{f}}/T$ versus $T$ plot and the entropy. Also shown are [lower inset in (a)] the low-temperature part of the heat capacity and a fit to the nuclear Schottky and (b) magnetic field dependence of heat capacity in PrSi.

Figure 8

Representative magnetization isothermals at various temperatures along (a) the $a$ axis ($H\parallel \left[100\right]$), (b) the $b$ axis ($H\parallel \left[010\right]$), and (c) the $c$ axis ($H\parallel \left[001\right]$). Only field increasing measurement data are included for each temperature.

Figure 9

Panels (a), (b), and (c) represent the temperature variation of magnetic entropy change ($-\Delta S_M$; along the three principal crystallographic directions $H\parallel \left[010\right]$, $H\parallel \left[001\right]$, and $H\parallel \left[100\right]$, respectively) around the magnetic transition region at various fields of PrSi.

Figure 10

Panels (a), (b), and (c) represent the field variation of magnetic entropy change ($-\Delta S_M$; along the three principal crystallographic directions $H\parallel$ [010], $H\parallel \left[001\right]$, and $H\parallel \left[100\right]$) around the magnetic transition region at different constant temperatures of PrSi.

Figure 11

Magnetic field variation of relative cooling power for PrSi along the [010] direction.