Roughness effects in uncompensated antiferromagnets

Abstract

Monte Carlo simulations show that roughness in uncompensated antiferromagnets decreases not just the surface magnetization but also the net magnetization and particularly strongly affects the temperature dependence. In films with step-type roughness, each step creates a new compensation front that decreases the global net magnetization. The saturation magnetization decreases non-monotonically with increasing roughness and does not scale with the surface area. Roughness in the form of surface vacancies changes the temperature-dependence of the magnetization; when only one surface has vacancies, the saturation magnetization will decrease linearly with surface occupancy, whereas when both surfaces have vacancies, the magnetization is negative and exhibits a compensation point at finite temperature, which can be tuned by controlling the occupancy. Roughness also affects the spin-texture of the surfaces due to long-range dipolar interactions and generates non-collinear spin configurations that could be used in devices to produce locally modified exchange bias. These results explain the strongly reduced magnetization found in magnetometry experiments and furthers our understanding of the temperature-dependence of exchange bias.

Investigation of Magnetotaxis of Reconfigurable Micro‐Origami Swimmers with Competitive and Cooperative Anisotropy

“…The outcome of this competition depends on the arrangement of the MNPs: in a scenario where the particles are evenly dispersed (e.g., as shown in Figures or a), there is no pronounced net magnetic easy axis and the PDM can be programmed by the external field by saturating the sample. In a scenario where the MNPs are aligned in chains, however, the dipole–dipole interactions along the chain become dominant, provided that interparticle distances in the chain are much smaller than distances between chains, and thus the PDM will always lie in the chain axis. Hence, the PDM will take the form of the chains, as shown in Figure (see S1, Supporting Information).…”

Thickness-Dependent and Magnetic-Field-Driven Suppression of Antiferromagnetic Order in Thin V5S8 Single Crystals

“…Confinement can affect the itinerant carriers, as seen in the thickness-dependent ρ(T), potentially impacting exchange processes. The effects of uncompensated surface spins may also be at play, 29 due to a possible lack of perfect AFM order at the crystal surfaces, which would be more important in crystals of reduced thickness. Thinner crystals are more strained due to their elastic interactions with the underlying substrate.…”

Interface-induced phenomena in magnetism

“…As examples, EuTe(111) films exhibit strongly reduced magnetization near the film surface [Schierle et al ., 2008], the magnetization of NiO(111) and NiO(100) films is stronger at the surfaces, such that surface order persists even above T N of bulk NiO [Marynowski et al ., 1999; Barbier et al ., 2004], while KMnF 3 (110) [Sinkovic et al ., 1985] and MnO(001) [Hermsmeier et al ., 1989; Hermsmeier et al ., 1990] surfaces exhibit ordering at temperatures that are twice as high as bulk T N . For antiferromagnets, the consequences of surface exchange modifications can be particularly dramatic, since the net spontaneous moment of the material is dominated by surfaces and defects [ e.g ., Charilaou and Hellman, 2014; Charilaou and Hellman, 2014, 2015a, 2015b]. …”