Partial order induced superconductivity in Fe²⁺ iron

Department of Physics, University of Sofia - 1164 Sofia, Bulgaria

^(a) naoum@phys.uni-sofia.bg

Received: 20 February 2019
Accepted: 17 May 2019

Abstract

In this letter, we address the Fe²⁺ state of iron with six 3d electrons. Five of them are localized with ferromagnetic order, while the sixth one is itinerant antiparallelly to the localized ones. We consider a spin-fermion model of 3d electrons and show that one can fix the parameters in the theory so that the calculated magnetization matches the experimentally measured one. With these parameters in mind we show that the sixth 3d electrons have well-defined Fermi surfaces, therefore the material is metal. Further on we consider an iron prepared by means of an applied external magnetic field upon cooling. We assume that the applied magnetic field is along the magnetic order of localized 3d electrons and antiparallel to the magnetic order of the itinerant sixth electron. Therefore, the applied field decreases the Zeeman splitting of the spin-up and spin-down sixth electrons. We focus on the quantum partial order (QPO) state which is obtained when the applied field compensates the Zeeman splitting so that the sixth 3d electrons do not contribute to the magnetism of iron and magnetic order is formed by means of localized 3d electrons. We obtain an effective Hamiltonian for iron in the (QPO) state and demonstrate that the spin triplet superconducting state with the T_1u gap symmetry may be a ground state.