Giant magnetocaloric effect in an exchange-frustrated ${\mathrm{GdCrTiO}}_5$ antiferromagnet

We report the role of exchange frustration on the magnetocaloric properties of ${\mathrm{GdCrTiO}}_5$. Due to the highly frustrated nature of magnetic interactions, in ${\mathrm{GdCrTiO}}_5$, the long-range antiferromagnetic ordering of ${\mathrm{Gd}}^{3+}$ moments occurs at a much lower temperature $T_N=0.9$ K and the magnetic cooling power enhances dramatically relative to that observed in several geometrically frustrated systems. Below 5 K, the isothermal magnetic entropy change ($-\mathrm{\Delta }{S}_{\mathrm{m}}$) is found to be 36 J ${\mathrm{kg}}^{-1}{\mathrm{K}}^{-1}$ for a field change ($\mathrm{\Delta }H$) of 7 T. $-\mathrm{\Delta }{S}_{\mathrm{m}}$ shows saturationlike behavior with decreasing $T$ down to 2 K and is reversible in nature. The adiabatic temperature change $\mathrm{\Delta }{T}_{\mathrm{ad}}$ is 15.5 K for $\mathrm{\Delta }H=7$ T. These magnetocaloric parameters are significantly larger than that reported for several potential magnetic refrigerants, even for small and moderate field changes. The present result not only suggests that ${\mathrm{GdCrTiO}}_5$ could be considered as a potential magnetic refrigerant at cryogenic temperatures but also promotes further studies on the role of exchange frustration on the magnetocaloric effect. In contrast, only the role of geometrical frustration on the magnetocaloric effect has been previously reported theoretically and experimentally investigated on very few systems.

Figure 1

The orthorombic crystal structure of ${\mathrm{GdCrTiO}}_5$. The polyhedra formed by chromium (Cr) and titanium (Ti) with oxygen (O) atoms are shown schematically.

Figure 2

Magnetic structure of $R{\mathrm{CrTiO}}_5$ and the arrow indicates the orientation of magnetic moment of $R^{3+}$ and ${\mathrm{Cr}}^{3+}$. In ${\mathrm{GdCrTiO}}_5$, the Gd moments order antiferromagnetically below 0.9 K but the Cr moments do not show any long-range ordering.

Figure 3

The x-ray diffraction pattern of the polycrystalline powder of ${\mathrm{GdCrTiO}}_5$ and the refinement parameters for the best fit result obtained from the profile fit are also shown.

Figure 4

The main panel shows the temperature dependence of magnetization for ${\mathrm{GdCrTiO}}_5$ at 0.05 T and the inset shows the Curie-Weiss fit to inverse susceptibility ($H$/$M$) at high temperature.

Figure 5

(a) The isothermal magnetization plots for ${\mathrm{GdCrTiO}}_5$ in the temperature range of 2–35 K and (b) the hysteresis loop at 2 K up to 2 T.

Figure 6

The temperature variation of $\mathrm{\Delta }{S}_{\mathrm{m}}$ for ${\mathrm{GdCrTiO}}_5$ calculated from the magnetization data and inset shows the field dependence of $\mathrm{\Delta }{S}_{\mathrm{m}}$ at 2 K.

Figure 7

The contour plot of $\mathrm{\Delta }{S}_{\mathrm{m}}$ as functions of temperature and magnetic field for ${\mathrm{GdCrTiO}}_5$.

Figure 8

(a) The zero-field heat capacity data for the ${\mathrm{GdCrTiO}}_5$ compound and the solid line is the combined Debye-Einstein fit. (b) The field dependence of heat capacity for ${\mathrm{GdCrTiO}}_5$. The arrow indicates the short-range ordering near 10 K.

Figure 9

The temperature variation of magnetic entropy with field for the ${\mathrm{GdCrTiO}}_5$ compound, whereas the red line represents the zero field entropy calculated from reported data [42] and the inset shows the variation of $\mathrm{\Delta }{S}_{\mathrm{m}}$ calculated from the heat capacity data.

Figure 10

The variation of entropy at different fields. The horizontal arrow from $a$ to $b$ indicates the adiabatic heating and $c$ to $d$ indicates the adiabatic cooling, whereas the vertical arrow indicates the isothermal entropy change for the magnetic field change 0–7 T.

Figure 11

The temperature dependence of $\mathrm{\Delta }{T}_{\mathrm{ad}}$ for ${\mathrm{GdCrTiO}}_5$ at different magnetic fields and the inset shows the final temperature $T_f$ as a function of the initial temperature $T_i$ in the adiabatic demagnetization process for different magnetic fields.

Figure 12

The main panel shows the temperature dependence of thermal conductivity for ${\mathrm{GdCrTiO}}_5$ whereas the red line shows the Debye fitting to the experimental data and the inset shows the anomaly near 150 K.