Fe nGeTe2 ( n =  3, 4, and 5) has recently attracted increasing attention due to its two-dimensional van der Waals characteristic and high temperature ferromagnetism, which makes promises for spintronic devices. A Fe(1) split site is an important structural characteristic of Fe5GeTe2, which makes it very different from other Fe nGeTe2 ( n =  3 and 4) systems. The local atomic disorder and short-range order can be induced by the split site. In this work, high-quality van der Waals ferromagnet Fe5GeTe2 single crystals were grown to study low-temperature transport properties. We found a resistivity upturn below 10 K. The temperature and magnetic field dependence of the resistivity are in good agreement with a combination of the theory of disorder-enhanced three-dimensional electron–electron and single-channel Kondo effect. The Kondo effect exists only at low magnetic fields [Formula: see text], while electron–electron interaction dominates the appearance for the low-temperature resistivity upturn. We believe that the enhanced three-dimensional electron–electron interaction in this system is induced by the local atomic structural disorder due to the split site of Fe(1). Our results indicate that the split site of Fe plays an important role for the exceptional transport properties.

In this work, the effect of uniaxial stress on the stability of magnetic skyrmion is studied by use of Monte Carlo simulations. The classical Heisenberg model with anisotropic exchanges and Dzyaloshinskii-Moriya interactions is applied to correlate the stress behavior. We calculate magnetization M and skyrmion number Q to estimate the phase transition points, use the spin configurations and their Fourier transform to determine the region of skyrmion state. The h − T phase diagram show the area of skyrmion state is larger with stress than without stress. These results are interpreted qualitatively by the energy competitions between Zeeman, exchanges and Dzyaloshinskii-Moriya interactions. The simulated results suggest that anisotropy induced by uniaxial stress can stabilize the skyrmion phase.

Magnetic frustration can induce interesting magnetic phases including skyrmion state in centrosymmetric materials. By means of Monte Carlo simulations, we theoretically study the frustrated J1-J2classical Heisenberg model on the triangular lattice. Both h-J2 and h-T phase diagrams show rich magnetic phases, and skyrmion state can be stabilized by J2. These results can be qualitatively explained by energy competitions, and indicate that skyrmion can be driven by the competition of short-range interactions in absence of DM interaction. This may help us to design and apply the skyrmion devices more easily in the future.

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