Nonsaturating magnetoresistance, anomalous Hall effect, and magnetic quantum oscillations in the ferromagnetic semimetal PrAlSi

摘要

We report a comprehensive investigation of the structural, magnetic, transport, and thermodynamic properties of single crystal PrAlSi, in comparison to its nonmagnetic analog LaAlSi. PrAlSi exhibits a ferromagnetic transition at T_C = 17.8 K which, however, is followed by two weak phase transitions at lower temperatures. The two reentrant magnetic phases can be suppressed by a small magnetic field of about 0.4 T and are proposed to be spin glasses or ferromagnetic cluster glasses based on dc and ac magnetic susceptibilities. Both the two compounds reveal large, nonsaturating magnetoresistance as a function of field. While Shubnikov-de Haas oscillations are absent in LaAlSi, they are clearly observed below about 25 K in PrAlSi, with an unusual temperature dependence of the dominating oscillation frequency F. It increases from F = 18 T at 25 K to F = 33 T at 2 K, hinting at an emerging Fermi pocket upon cooling into the ordered phase. Specific-heat measurements indicate a non-Kramers magnetic doublet ground state and a small overall crystal electric field splitting of the Pi~(3+) multiplets of less than 100 K; Hall-effect measurements show a large anomalous Hall conductivity amounting to ～2000 Ω~(-1) cm~(-1) below T_C These results suggest that PrAlSi is a new system where a small Fermi pocket is strongly coupled to local-moment magnetism. Whether topological state is also involved remains an intriguing open problem.