Mechanism of magnetic phase transition in correlated magnetic metal: insight into metallic ferromagnet Fe3-δGeTe2

Developing a comprehensive magnetic theory of correlated itinerant magnets is a challenging task due to the difficulty in reconciling both local moments and itinerant electrons. In this work, we investigate the microscopic process of magnetic phase transition in ferromagnet metal Fe _3-δ GeTe ₂ . A new paradigm is proposed to describe the magnetic phase transition in correlated metallic ferromagnets, where Hund's coupling dominates the spectral weight transfer between different spin channels, rather than spin-splitting as described by the Stoner model. We recognize that our theory should be universal for itinerant magnets. Additionally, we reveal an efficient way to achieve novel quantum states from various competing orders in multi-site crystal structures. Our research shows that Fe1 are proximate to Mott physics, while Fe2 exhibit Hund physics due to their distinct atomic environments. These competing orders work together to produce heavy fermion behavior within ferromagnetic long-range order through well-defined quasiparticle bands, which are promoted by Hund's coupling and further hybridized with relative itinerant bands. The complex interactions of competing orders drive correlated magnetic metal to a new frontier for discovering outstanding quantum states and exotic phenomena in condensed matter physics.