A unified theory of ferromagnetic quantum phase transitions in heavy fermion metals

Motivated by the recent discovery of a continuous ferromagnetic quantum phase transition in CeRh$_6$Ge$_4$ and its distinction from other U-based heavy fermion metals such as UGe$_2$, we develop unified explanation their different ground state properties based on an anisotropic Kondo-Heisenberg model. We employ improved large-$N$ Schwinger boson approach predict full diagram containing both for large magnetic anisotropy first-order transitions relatively small anisotropy. Our calculations reveal three phases including half-metallic spin selective Kondo insulator with constant magnetization. The Fermi surface topologies are found to change abruptly between phases, consistent that observed UGe$_2$. At finite temperatures, development hybridization well above long-range order relocalization near transition, good agreement band measurements CeRh$_6$Ge$_4$. results highlight importance provide theory understanding metals.