Low-temperature antiferromagnetic order of Ni 4 single-molecule magnets

The low-temperature specific heat of Ni4 single-molecule magnets (SMMs) is measured in a PPMS He-3 system. The temperature- dependent specific heat of Ni4 SMMs shows an antiferromagnetic phase transition at 0.91 K. The experimental results are in good consistency with Monte Carlo simulation of 3D-Ising model, indicating two independent diamond-like antiferromagnetic structures with an exchange energy J = 0.020 K in Ni4 system.