Magnetic Compton profile in uranium chalcogenide compounds UX (X=Se, Te)

Abstract

Magnetic Compton scattering is a well-established technique to investigate the momentum distribution of electrons with unpaired spins in ferroand ferrimagnetic materials, using circularly polarized X-rays. There are some features inherent to the magnetic Compton scattering technique under the impulse approximation [1]. One is that the magnetic Compton profile (MCP) sees only ‘spin’ contribution to the magnetic moment, i.e. no orbital contribution can be reflected in MCP. Therefore, if the total magnetization is measured by some independent technique, one can separately obtain spin and orbital contributions to the magnetic moment by combining MCP with the traditional magnetization measurement [2]. The second is that the momentum distributions of different groups (3d, 4f, 5f, conduction-like electrons, etc.) have different characteristic MCPs, therefore one can deduce site-selective magnetic information even in alloys and compounds. Uranium monochalcogenide compounds UX (X = S, Se, Te) undergo the ferromagnetic phase transition at the temperature Tc = 180, 174, and 104 K, respectively. The magnetic moment of UX increases with increasing atomic number of chalcogenide element. This is believed to come from the degree of localization of 5f electrons because the U–U separation inferred from the structural data increases from US to UTe. However, the magneto-optical properties do not show monotonic correspondence against the atomic number of chalcogenide element; i.e. Kerr rotation angle of US, USe and UTe are 2.6°, 3.3° and 3.1°, respectively [3], which suggest non-simple scheme of spin–orbit interaction between U and chalcogenide element. Therefore, it would be interesting to study the spin and orbital contribution of UX compounds separately by magnetic Compton scattering. In this paper, we report MCP of Use and UTe which have been carried out at AR-NE1 station of KEK, Japan, and try to separate the spin and orbital contributions of magnetic moments by combining MCP with the magnetization measurement. Furthermore, we discuss the degree of localization of 5f electrons of these samples by decomposing the MCP into localized component and itinerant component.