We report our systematic investigation of structural, magnetic, and magnetocaloric properties of double
perovskite compounds Ho2FeMnO6, Ho2CoMnO6, and Ho2NiMnO6, which crystallize into monoclinic crystal
structure with P21/n space group. The magnetic phase transition temperatures are determined to be 7.5 K for
Ho2FeMnO6, 69 K for Ho2CoMnO6, and 71.5 K for Ho2NiMnO6, where Ho2FeMnO6 exhibits an antiferromagnetic
to paramagnetic phase transition, while Ho2CoMnO6 and Ho2NiMnO6 exhibits ferromagnetic to paramagnetic
phase transitions. The magnetic entropy change ( ΔSM), which are found to be 10.2, 3.4 and 4.7 J/kgK at ΔH =
7 T for Ho2FeMnO6, Ho2CoMnO6, and Ho2NiMnO6 samples, respectively. The magnetic and magnetocaloric
characteristics of double perovskite compounds are well explained based on structural and electronic properties.
For future applications, our quantitative method provides a guideline for magnetic property engineering of
double perovskite systems containing ferromagnetic 3d transition metals.