Room temperature d0 ferromagnetism in PbS films: nonuniform distribution of Pb vacancies

Abstract

Because of the importance of ferromagnetism at room temperature, we search for new materials that can exhibit a non-vanishing magnetic moment at room temperature and at the same time can be used in spintronics. The experimental results indicate that d⁰ ferromagnetism without any magnetic impurities takes place in PbS films made of close-packed lead sulfide nanoparticles of 30 nm. To explain the existence of the d⁰ ferromagnetism, we propose a model where various PbS bulk and surface configurations of Pb-vacancies are analyzed. The bulk configurations have a zero magnetic moment while the two surface configurations with Pb vacancies with the same non-vanishing magnetic moments and lowest ground state energies contribute to the total magnetization. Based on the experimental value of the saturation magnetization, 0.2 emu g⁻¹, we have found that the calculated Pb vacancy concentration should be about 3.5%, which is close to typical experimental values. Besides being very important for applications, there is one feature of PbS d⁰ ferromagnetism that makes this material special for fundamental research: PbS ferromagnetism can exhibit topologically driven spatial magnetic moment distributions (e.g., magnetic skyrmions) due to large spin–orbit coupling.