High-field magnetization and magnetodielectric effect in a Ni2NbBO6 single crystal

We have studied the magnetization, dielectric permittivity, thermal expansion, and magnetostriction of Ni2NbBO6 single crystals. Different from that of the ab plane, the c axis magnetization approaches zero at low magnetic fields and a spin-flop transition happens around HSF = 3.65 T. The results indicate that the c axis is the hard axis and the ab plane is the easy plane. The high-field isothermal magnetization measured at T = 4.2 K reveals that the saturation magnetic field is Hs = 17 T, above which the magnetic structure changes from canted-antiferromagnetic order to ferromagnetic order with the saturation magnetic moment mu eff = 2.40 mu B/Ni2+ Below antiferromagnetic transition temperature TN, an unusual negative thermal expansion phenomenon is detected along the b axis and it can be interpreted by the magnetic structural variation. Based on the magnetization and the magnetostriction data, the magnetic field-temperature phase diagram of Ni2NbBO6 is constructed. The magnetodielectric effect confirms the existence of magnetoelectric coupling in Ni2NbBO6.