High ferromagnetic transition temperature in PbS and PbS:Mn nanowires

Spontaneous magnetization measured in the temperature range 5-300 K with high ferromagnetic transition temperature (T(c)) has been observed in both undoped and Mn doped (2-8 mol %) PbS nanowires (diameter 30 nm) in polymer. For undoped sample, we find T(c) ~ 290 K while for doped samples T(c) varies between 310-340 K depending on Mn concentrations. Both T(c) and coercive fields are critically dependent on Mn concentrations. Coercive fields show a T(0.5) dependence with temperature for a moderate concentration of Mn (4 mol %) in PbS while it deviates from T(0.5) behavior for higher Mn concentrations. Anionic defects arising out of nonstoichiometric growth is solely responsible for the observed magnetism in undoped PbS nanowires. The role of intrinsic strain along with reduced dimensionality in determining such high T(c) and overall magnetizations has been discussed.