Magnetic neutron diffraction under pressures up to 43 GPa. Study of the EuX and GdX compounds

Abstract

We present some recent results on magnetic neutron studies at pressures above 40 GPa. We used diamond and sapphire anvil pressure cells for low temperature neutron studies and a powder diffractometer specialized for high pressure studies. Focusing systems and low-background conditions allowed us to study samples with volumes as small as 0.001 mm3 in a diamond anvil cell at a pressure of 50 GPa. This technical progress allowed us to obtain new results in studies of “textbook” magnetic insulators EuX (X = S, Se, Te) and GdX (X = As, Sb, Bi). We found new magnetic phases. In the Eu-chalcogenides we observed a strong anion-dependent increase of the ferromagnetic exchange with decreasing lattice constant. In contrast, in the GdX compounds the antiferromagnetic order remains stable up to a pressure of 43 GPa. We show the importance of our results to understand the origin of indirect exchange interactions in magnetic semiconductors with well localized magnetic shells.