Magnetic-Field-Driven Ising Quantum Criticality of Two-Dimensional Square-Lattice Antiferromagnet Cr(dien)(O$_{2})_{2}$.H$_{2}$O

We report on a systematic study of magnetically driven quantum phase transition in a new compound based on Cr(IV). The compound, Cr(dien)(O$_{2})_{2}$.H$_{2}$O, is a low dimensional antiferromagnet with a Neel temperature T$_{N}$ of 2.55 K in zero field. We have used torque magnetometry, heat capacity and magnetocaloric-effect measurements down to 200 mK, to obtain a complete magnetic phase diagram. A detailed analysis of the dependence of T$_{N}$ on magnetic field using the power law T$_{N}$ $\sim $ (H$_{c}$-H)$^{\alpha }$ yielded the critical exponent $\alpha $ = 2.01$\pm $0.02, with H$_{c}$ = 12.392$\pm $0.003 T, indicating that this system behaves like a 3-d Ising magnet at low temperatures.