Comparison of the nature of magnetism in α-Ni(OH)2 and β-Ni(OH)2

For the two stable phases of Ni(OH)(2), viz. alpha-Ni(OH)(2) and beta-Ni(OH)(2), structural and magnetic properties are compared employing x-ray diffraction (XRD), scanning electron microscopy/transmission electron microscopy (TEM/SEM), and variation of the magnetization (M) with temperatures (2-350K) and magnetic fields (up to approximate to 65 kOe). Both phases crystallize in the layered hexagonal structure with a=3.04 angstrom (3.12 angstrom) and c=23.6 angstrom (4.67 angstrom) for the alpha(beta) phase with clear evidence for turbostraticity in the alpha-phase. From TEM/SEM, the beta-phase consists of nanoplates of dimensions 30(10) x 3(1) nm, whereas the alpha-phase has flowerlike morphology with petal thickness approximate to 5(1) nm. The low-field M versus T data for the zero-field-cooled/field cooled cases bifurcates at T-p=25 K (3 K) for the beta(alpha) phase. For T > T-p, Curie-Weiss variation of M versus T is observed yielding positive theta=20.6 K (2 K) with mu=2.95 mu(B) (3.13 mu(B)) for the Ni2+ ions in the beta(alpha) phase. The M versus H data at 2 K shows antiferromagnetic (ferromagnetic) like variation for the beta(alpha) phase with dM/dH showing peaks at H-c1=28 kOe and H-c2=55 kOe for the beta-phase. It is concluded that beta-Ni(OH)(2) is a metamagnet for T < T-N=25 K, whereas alpha-Ni(OH)(2) is a hard ferromagnet with T-c=13 K and domain structure for H < 5 kOe. (C) 2010 American Institute of Physics. [doi:10.1063/1.3358015]