Abstract
We establish the low-temperature phase diagrams of the spin- and spin-1 Kondo lattice models as a function of the conduction-band filling and the exchange coupling strength in the regime of ferromagnetic effective exchange interactions (, ). We show that both models have several distinct ferromagnetic phases separated by continuous Lifshitz transitions of the Fermi-pocket vanishing or emergence type: one of the phases has a true gap in the minority band (half metal with magnetization rigidity), the others only a pseudogap. The spin- model has the half-metal phase, two topologically different pseudogap phases, and a paramagnetic state for very large . The spin-1 model has the half-metal phase and a single pseudogap phase with an electron pocket. We find that, quite generically, ferromagnetism and Kondo screening coexist rather than compete both in spin- and spin-1 models. We establish the hysteretic behavior of the systems in an external magnetic field: spin-flop transitions preempt further Lifshitz transitions at finite magnetic field. We establish a “ferromagnetic Doniach diagram”: in the spin- model the Curie temperature peaks near and goes to zero, while in the spin-1 model it saturates.
- Received 10 January 2013
DOI:https://doi.org/10.1103/PhysRevB.88.054431
©2013 American Physical Society