Observation of ferromagnetic ordering in a stable α-Co(OH)2 phase grown on a MoS2 surface

Because of the potential application of Co(OH)(2) in a magnetic cooling system as a result of its superior magnetocaloric effect many people have investigated magnetic properties of Co(OH)(2). Unfortunately, most of the works have been carried out on the beta-Co(OH)(2) phase due to the fact that the alpha-Co(OH)(2) phase is very unstable and continuously transformed into the stable beta-Co(OH)(2) phase. However, in the present work, using a MoS2 sheet as a two-dimensional template, we have been able to synthesize a stable alpha-Co(OH)(2) phase in addition to a beta-Co(OH)(2) phase by varying the layer thickness. It is seen that for thinner samples the beta phase, while for thicker samples alpha phase, is grown on the MoS2 surface. Magnetic measurements are carried out for the samples over the temperature range from 2 to 300 K and it is seen that for the beta phase, ferromagnetic ordering with fairly large coercivity (1271 Oe) at 2 K is obtained instead of the usual antiferromagnetism. The most interesting result is the observation of ferromagnetic ordering with a transition temperature (Curie temperature) more than 100 K in the alpha-Co(OH)(2) phase. Complete saturation in the hysteresis curve under application of very low field having coercivity of similar to 162 Oe at 2 K and 60 Oe at 50 K is obtained. A thin stable alpha-Co(OH)(2) phase grown on MoS2 surface with very soft ferromagnetic ordering will be very useful as the core material in electromagnets.