Successive antiferromagnetic and ferromagnetic phase transitions in PrRu₂Al₂B: A comprehensive study of magnetic transitions

In this study, we employed a comprehensive approach, utilizing magnetic susceptibility, zero-field muon spin relaxation (ZF-μSR), and neutron diffraction techniques, to elucidate the complex magnetic state of PrRu₂Al₂B. This compound, displaying an Ising-type ferromagnetic ground state, crystallizes in a tetragonal CeCr₂Si₂C-type structure with the space group P4∕mmm. Our ZF-μSR measurements and susceptibility investigations collaboratively unveiled distinct features in the magnetic behavior of PrRu₂Al₂B. A noticeable cusp emerged in both measurements at T_N = 26 K, indicative of an antiferromagnetic transition, whereas a sharp increase materialized around T_C = 11 K, signifying the commencement of ferromagnetic ordering. Below T_N, the muon asymmetry underwent a substantial two-thirds reduction, accompanied by a deceleration in the rate of muon depolarization. Complementary to these findings, neutron diffraction measurements provided crucial insights into the spin-density wave present below T_N and above T_C. A longitudinal incommensurate spin-density wave was observed, with the propagation vector k = (0, 0, k_z) exhibiting a steady evolution within this temperature range. This study establishes PrRu₂Al₂B as an intriguing model system for investigating the global phase diagram of ferromagnetic heavy-fermion metals, particularly in the context of magnetic frustration. The insights garnered from our investigation not only contribute to the comprehension of PrRu₂Al₂B's magnetic behavior but also hold broader implications for unraveling the magnetic complexities in analogous systems, such as CeRu₂Al₂B.