The nature of the magnetism in quasi-2D layered α-Ni(OH)2

The two layered hexagonal hydroxides of Ni are β-Ni(OH)2 and α-Ni(OH)2; β-Ni(OH)2 is now known to be an antiferromagnet whereas the nature of the magnetism in α-Ni(OH)2 is not yet well established. Here, the magnetic properties of α-Ni(OH)2 with lattice parameters a = 3.02 Å and c = 8.6 Å, and flower-like morphology with petal thickness of ≃ 50 Å are reported. Temperature (2-300 K) and magnetic field (up to 65 kOe) dependence of the magnetization and ac susceptibility at f = 0.1-1000 Hz were measured. Analysis of the data yields ferromagnetic ordering in the system with TC ≃ 16 K. In addition, a nanosize related blocking temperature TB = 8 K and spin-glass-like ordering of the surface spins near 3.5 K are inferred from the ac frequency and dc magnetic field dependence of these transitions. Fitting to the high temperature series and quasi-2D nature of the system is used to determine J1/kB = 4.38 K (J2/kB = 0.14 K) for the intraplane (interplane) exchange coupling between the Ni2+ ions. (paper)