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

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 ${\mathrm{Pr}}^{3+}$ multiplets of less than 100 K; Hall-effect measurements show a large anomalous Hall conductivity amounting to $\ensuremath{\sim}2000\phantom{\rule{4pt}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ 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.