Magnetic Field–Temperature Phase Diagram of CeCoSi Constructed on the Basis of Specific Heat, Magnetoresistivity, and Magnetization Measurements: Single Crystal Study

Abstract

The Ce-based metallic compound CeCoSi with a tetragonal structure exhibits successive phase transitions: a hidden ordering, whose order parameter is unidentified, at T0 ∼ 12 K and an antiferromagnetic ordering at TN = 9.4 K. [Tanida et al., J. Phys. Soc. Jpn. 88, 054716 (2019).] We performed specific heat, magnetoresistivity (MR), and magnetization (M) measurements for single crystals of CeCoSi at low temperatures in magnetic fields B of up to 14 T and constructed detailed magnetic field–temperature phase diagrams for both 𝐵∥[100] and [001]. In the longitudinal MR measurements for 𝐵∥[100], the sign of MR changes from negative in a paramagnetic state to positive in the hidden ordered state, which suggests a change in electronic state across T0. In addition, the longitudinal MR and magnetization processes for 𝐵∥[100] show anomalies upon the application of B in both ordered states, suggesting the presence of B-induced regions. Similar B-induced regions may exist in the magnetic phase diagram for 𝐵∥[001]. The emergence of B-induced regions may be attributed to a change in the symmetry of the order parameter or domain alignment on applying B.