We investigated the anisotropy of the magnetic and magnetocaloric properties of single-crystalline double-perovskite $\mathrm{T}{\mathrm{b}}_2\mathrm{CoMn}{\mathrm{O}}_6$, which crystallizes in a monoclinic $P{2}_1/n$ structure. Due to dissimilar magnetic anisotropy, the ferromagnetic order of the $\mathrm{C}{\mathrm{o}}^{2+}$ and $\mathrm{M}{\mathrm{n}}^{4+}$ moments emerges along the $c$ axis at $T_{\mathrm{C}}=100\mathrm{K}$, and the larger $\mathrm{T}{\mathrm{b}}^{3+}$ moments align perpendicular to the $c$ axis, below $T_{\mathrm{Tb}}=15\mathrm{K}$. The intricate temperature development of the metamagnetism along the $c$ axis results in a large negative change in the magnetic entropy at low temperature. On the other hand, the larger but almost reversible magnetization, perpendicular to the $c$ axis, results in a small and positive entropy change. This highly anisotropic magnetocaloric effect (MCE) leads to a giant rotational MCE, estimated to be $20.8\mathrm{J}/\mathrm{kg}\mathrm{K}$. Our findings, based on the magnetic anisotropy in $\mathrm{T}{\mathrm{b}}_2\mathrm{CoMn}{\mathrm{O}}_6$, enrich fundamental and applied research on magnetic materials, considering the distinct magnetic characteristics of double perovskites.

• Received 7 September 2018

DOI:https://doi.org/10.1103/PhysRevB.98.174424