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

• Published in: Physical chemistry chemical physics : PCCP Vol. 2; no. 47; pp. 2984 - 2981
• Main Authors: Pimachev, Artem, Rimal, Gaurab, Nielsen, Robert D, Tang, Jinke, Dahnovsky, Yuri
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 05.12.2018
• Subjects: Configurations; Ferromagnetism; Hypothetical particles; Lead sulfides; Magnetic moments; Magnetic saturation; Magnetism; Magnetization; Nanoparticles; Particle theory; Room temperature; Spin-orbit interactions; Spintronics; Vacancies
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c8cp04882g

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 d 0 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 d 0 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 d 0 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. We experimentally find room temperature ferromagnetism in PbS nanoparticles and theoretically attribute this to the Pb-vacancies located on the surface.