Ambient effect on the Curie temperatures and magnetic domains in metallic two-dimensional magnets

The emergent magnetic two-dimensional (2D) materials provide ideal solid-state platforms for a broad range of applications including miniaturized spintronics, nonreciprocal optics, and magnetoelectric sensors. Owing to the general environmental sensitivity of 2D magnets, the understanding of ambient effects on 2D magnetism is critical. Apparently, the nature of itinerant ferromagnetism potentially makes metallic 2D magnets insensitive to environmental disturbance. Nevertheless, our systematic study showed that the Curie temperature of metallic 2D Fe3GeTe2 decreases dramatically in the air but thick Fe3GeTe2 exhibits self-protection. Remarkably, we found the air exposure effectively promotes the formation of multiple magnetic domains in 2D Fe3GeTe2, but not in bulk Fe3GeTe2. Our first-principles calculations support the scenario that substrate-induced roughness and tellurium vacancies boost the interaction of 2D Fe3GeTe2 with the air. Our elucidation of the thickness-dependent air-catalyzed evolution of Curie temperatures and magnetic domains in 2D magnets provides critical insights for chemically decorating and manipulating 2D magnets.

Direct observation of competition between charge order and itinerant ferromagnetism in vdW crystal Fe5-xGeTe2

The interplay of symmetry-breaking ordered states, such as superconductivity, charge density waves (CDW), magnetism and pseudogap, is a fundamental issue in correlated system. CDW and antiferromagnetism often coexist in the proximity of phase diagram region in cuprates. It is also worthy nothing that different order states appear in a situation on comparable temperature scales, so these orders are intertwined and competing on the same footing. The magnetism of vdW material Fe5-xGeTe2 with the one of the highest reported bulk Curie temperatures, is found to be sensitive to thermal history and external magnetic field. However, the temperature-dependent magnetization with two characteristic points still lacks a unified picture to describe. Using angle-resolved photoemission spectroscopy, scanning tunneling microscopy, magnetic properties measurements, and the first-principles calculations, the complex yet intriguing magnetic behaviors are gradually unveiled. A competition mechanism between charge order and ferromagnetism is proposed and firmly observed by experimental measurements. As the ferromagnetic order strengthens at low temperature, the charge order will be suppressed. Exchange splitting in itinerant ferromagnetism plays a significant role in the temperature evolution of band structure and causes a Lifshitz transition, which provides more control means to realize novel devices at room temperature.

Observation of itinerant ferromagnetism and coupled magnetoresistance in a spinel CuCo2S4

We report the existence of ferromagnetism in the thiospinel compound CuCo2S4 with Tc ~125K. The magneto-electronic transport of the CuCo2S4 demonstrates a metallic conductivity and positive magnetoresistance at high temperature....