UI3 – 5f-electron magnetic van der Waals material

Abstract

We grew high-quality single crystals of the 5f electron van der Waals compound UI3 and investigated them by measurements of specific heat and magnetization as function of temperature and magnetic field. UI3 behaves as an antiferromagnet with a first-order magnetic phase transition at the Neél temperature TN ​= ​2.65 ​K. It is characterized by a sharp symmetric specific-heat peak which is gradually shifted to lower temperatures by increasing magnetic field applied along either the a- or b-axis. The behavior in magnetic field reveals orthorhombic magnetocrystalline anisotropy with the hard magnetization direction along the c-axis. The 2-K a- and b-axis magnetization curves exhibit a metamagnetic transition at the critical field μ0Hc ​≈ ​3 ​T and ≈ 1.8 ​T, respectively. In higher fields, when the long-range antiferromagnetism is suppressed by a metamagnetic transition, signs of short-range magnetic ordering of antiferromagnetic correlations in the paramagnetic state show up both in specific heat and magnetization. The anomalous S-shape field dependence of a-axis magnetization well above Hc can be understood as the crossover from the correlated paramagnetic regime to the high-field polarized paramagnet. The magnetic phase diagrams for the magnetic field applied along the a- and b-axis, respectively, designed using the mentioned experimental results are presented. We have also found that the UI3 crystals are easily cleavable which predisposes this material for direct investigation of 5f electron magnetism in the 2D limit on exfoliated atomically thin samples.