Magnetic Properties of nickel hydroxides layers 30A apart obtained by intercalation with dodecyl sulfate ion

Magnetic systems with reduced dimensionality make good test beds for checks on theoretical models [1]. Here, changes in the nature of magnetic ordering in quasi-2d system of layered Ni hydroxides (LH-Ni-) with variations in the interlayer spacing c are investigated. Magnetic properties of LH-Ni-DS with c $\approx $ 30 A$^{\circ}$ synthesized by intercalating dodecyl sulfate ion, (C$_{12}$H$_{25}$OSO$_{3})^{-}$ between the layers are compared with those of LH-Ni-Ac (c $\approx $ 8.5 A$^{\circ}$ ) containing the acetate (Ac) ligand [2]. Measurements included those of magnetization M vs. T and H, ac susceptibilities (f $=$ 0.1 Hz - 1000 Hz) and EMR (Electron Magnetic Resonance) spectra at 9.28 GHz. Results show that just like LH-Ni-Ac, LH-Ni-DS also orders ferromagnetically but with T$_{c\, }\approx $ 23 K about 45 {\%} larger than T$_{c\, }\approx $ 16 K reported for LH-Ni-Ac.[2]. In EMR studies, linewidth is strongly temperature-dependent, decreasing with decreasing T from 300 K, reaching a minimum near 45 K and then increasing sharply for T \textless\ 45 K, the latter due to short range magnetic ordering. These results differ with the model of Drillon et al [3] in which interlayer dipolar interaction between clusters of correlated spins in the layers yields T$_{C}$ nearly independent of c. Roles of magnetic anisotropy and exchange constants in determining T$_{C}$ in the LH-Ni systems is discussed.\\[4pt] [1]. ``Magnetic properties of layered transition metal compounds'' L.J. deJongh , Editor.\\[0pt] [2]. J.D. Rall {\&} M.S. Seehra, J. Phys.:Condens.Matter 24, 076002(2012).\\[0pt] [3]. M. Drillon et al, Phys.Rev.B65, 104404 (2002).