Anisotropic Magnetocaloric Effect in Single Crystalline NiTa$_2$O$_6$

Magnetic susceptibility and heat capacity measurements were made on the low-dimensional antiferromagnet NiTa$_2$O$_6$. The antiferromagnetic structure most consistent with our measurements is the two sub-lattice model proposed by Law et al.\footnote{Law et al., \textit{Phys. Rev. B.} \textbf{89}, 014423 (2014).} in which magnetic moments in the z = 0 plane are aligned parallel to [110] and those in the z = 1/2 plane are aligned parallel to [1$\bar{1}$0]. Applying a magnetic field along [110] causes the peak in the heat capacity to split into two with one remaining at $T_N$ and the other shifting to lower temperatures as the field is increased with a maximum $\Delta T$ $\sim$ 3 K at 8 T. This splitting indicates that each sub-lattice orders at different N\'eel temperatures. Calculation of the magnetic entropy change associated with an increase in magnetic field($\Delta S_m(T, \Delta H$)) reveals $\Delta S_m(T, \Delta H$) $\sim$ 0.7 J/kg K for $H \parallel$ [110] and $\Delta S_m(T, \Delta H$) $\sim$ 0 J/kg K for $H \parallel$ [001] if $\Delta H$ = 8 T. This anisotropy in the magnetocaloric effect suggests that rotating the sample in constant magnetic field will result in a change in sample temperature.