Magnetism of UCo₂Si₂Single Crystal Studied under Applied Magnetic Field and Hydrostatic Pressure

Abstract

UCo 2 Si 2 is an antiferromagnet below T N = 82.4 K. The magnetic ordering is accompanied by the pronounced anomalies of resistivity, which are very different for the current direction along the a-and c-axis. Evolution of the T N -related resistivity features with increasing hydrostatic pressure up to 7.3 GPa was studied in order to reveal the pressure effects on magnetism in UCo 2 Si 2 . The T N value is found to decrease with increasing pressure; the critical pressure of collapse of ordered magnetism is estimated as 7.8. GPa.KEYWORDS: uranium compounds, specific heat, resistivity under hydrostatic pressure IntroductionUCo 2 Si 2 crystallizes in the orthorhombic ThCr 2 Si 2 -type crystal structure. A neutron powder diffraction experiment revealed that the compound is antiferromagnetic (AF) at temperatures below T N = 85 K. The magnetic moment was observed only at the U atom and amounts to 1.42(5) B at 4.2 K. The collinear magnetic structure is built of ferromagnetic basal-plane layers of U magnetic moments (aligned along the c-axis) with the + + stacking along the c-axis [1]. The so far reported magnetic data were obtained only on polycrystals and the results were rather contradictory [1,2]. This motivated us to grow a single crystal by Czochralski method and characterize it by measuring the specific heat (C), magnetization (M), and electrical resistivity ( ) with respect to temperature and magnetic field applied along the a-and c-axis. The T N -related features on the (T) curve were used to monitor the hydrostatic pressure effect on the U 5f-electron magnetism.

Peculiar magnetism of UAu2Si2

“…It may be associated with the opening of a gap on the Fermi surface due to the phase transition. This kind of anomaly in electrical resistivity suggestive of the reduction of the carrier number is also observed in other uranium 1-2-2 compounds, such as URu 2 Si 2 23 , UCo 2 Si 2 24 , and UNi 2 Ge 2 25 . At lower temperatures the resistivity finally decreases with decreasing temperature.…”

High-field magnetism and magnetoacoustics in uranium intermetallic antiferromagnets

“…Results of previous studies of the magnetization, electrical resistivity and specific heat performed on a UCo 2 Si 2 single crystal [5] point to T N ¼83 K. The strong anisotropy is preserved in the paramagnetic range as well. The magnetic susceptibility along the moment direction (the c-axis in UT 2 X 2 ) is much larger than along the basal-plane and obeys the Curie-Weiss law with an effective moment m eff ¼2.55 m B and paramagnetic Curie temperature Y p ¼ À29 K. The w (T) curve along the a axis is smooth and does not obey the Curie-Weiss law.…”

“…In this work we used the same UCo 2 Si 2 crystals as in Ref. [5] (the lattice parameters are a ¼392.1 pm and c ¼963.9 pm).…”

Magnetic and magnetoelastic properties of UCo2Si2as studied by high-field magnetization and ultrasound measurements

“…Under pressure, T N has been found to decrease and the estimated relatively low critical pressure (∼8 GPa) for the loss of magnetic order in UCo 2 Si 2 points to an itinerant character of the magnetism. 5,6 Other UT 2 X 2 compounds exhibit more evolved magnetic phase diagrams than UCo 2 Si 2 . In particular, UNi 2 Si 2 has three ordered phases: a ferrimagnetic, an AF type-I, and an incommensurate AF phase.…”