By means of powder neutron diffraction we investigate changes in the magnetic structure of the coplanar non-collinear antiferromagnet Mn3Ge caused by an application of hydrostatic pressure up to 5 GPa. At ambient conditions the kagomé layers of Mn atoms in Mn3Ge order in a triangular 120 • spin structure. Under high pressure the spins acquire a uniform out-of-plane canting, gradually transforming the magnetic texture to a non-coplanar configuration. With increasing pressure the canted structure fully transforms into the collinear ferromagnetic one. We observed that magnetic order is accompanied by a noticeable magnetoelastic effect, namely, spontaneous magnetostriction. The latter induces an in-plane magnetostrain of the hexagonal unit cell at ambient pressure and flips to an out-of-plane strain at high pressures in accordance with the change of the magnetic structure. arXiv:1805.09372v2 [cond-mat.str-el]

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We have used high precision neutron diffraction and ab initio calculations to investigate the behavior of the magnetism of spinel magnetite ͑Fe 3 O 4 ͒ under pressure in the 0-10 GPa range and at temperatures of 130-300 K. We find a significant but continuous decrease of the magnetic moments at both the A and B sites to at least 10 GPa, as well as an absence of any detectable pressure dependence of the oxygen atomic parameter. The data indicate a very weak dependence of the saturation moment on pressure and temperature and rule out unambiguously a transition from inverse to normal spinel in the P / T range investigated. Consequently, charge ordering cannot be precluded as the origin of the Verwey transition under pressure.

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We report high-pressure neutron diffraction data on the Morin-transition TM in α-Fe2O3 hematite, up to 8 GPa and under hydrostatic conditions. We find a strictly linear pressure coefficient of ∂TM /∂P = +27 ± 1 K/GPa with no evidence for intermediate magnetic states as indicated by all previous non-hydrostatic measurements. The behaviour of TM is highly regular and can well be explained within the framework of Artman et al.'s single-ion model if a change of the single-ion anisotropy energy by +1%/GPa is assumed. Such a value seems not to be unusual for iron oxides.