Ferromagnetic kinetic exchange interaction in magnetic insulators

Abstract

The superexchange theory predicts dominant antiferromagnetic kinetic interaction when the orbitals accommodating magnetic electrons are covalently bonded through diamagnetic bridging atoms or groups. Here we show that explicit consideration of magnetic and (leading) bridging orbitals, together with the electron transfer between the former, reveals a strong ferromagnetic kinetic exchange contribution. First-principles calculations show that it is comparable in strength with antiferromagnetic superexchange in a number of magnetic materials with diamagnetic metal bridges. In particular, it is responsible for a very large ferromagnetic coupling (−10 meV) between the iron ions in a Fe 3+-Co 3+-Fe 3+ complex. Furthermore, we find that the ferromagnetic exchange interaction turns into antiferromagnetic by substituting the diamagnetic bridge with magnetic one. The phenomenology is observed in two series of materials, supporting the significance of the ferromagnetic kinetic exchange mechanism.

Vibronic order and magnetism in cubic 5d 1 double perovskite compounds

“…We have to quantitatively construct model Hamiltonian based on the first principles based microscopic interactions. In particular, the elastic coupling plays a crucial role: to adequately describe the elastic coupling in the Jahn-Teller crystals, the Green's function based method would be indispensable [44,37].…”

“…Let us derive an effective model for the low-energy phenomena. The energy scales of the microscopic interactions are in the order of Coulomb (U ≈ 3 eV [7,35]), spin-orbit (λ ≈ 0.25 − 0.35 eV [16,33,36]), electron transfer (t ≈ 50 meV) and Jahn-Teller ( ωg ≈ 50 meV [33]), and elastic coupling [37]. Thus, we consider the interactions with the larger energy scales.…”

Metal replacement in the syntheses of MAMBMC heterometallic metal‐string complexes: MPdM'(dpa)4Cl2

“…To date, there is no explicit model that can be applied to interpret the superexchange mediated by the d orbitals of non-covalent and diamagnetic metal ions. [42,43] Nevertheless, we may apply the Goodenough-Kanamori rules of the M-O-M model with linear structures, where the doubly occupied p z orbital of the oxygen anionic mediator is replaced by the doubly occupied d z2 orbital of the diamagnetic Pd II. [44][45][46] The virtual electron transfer from the half-filled d z 2 orbital of Ni II to the doubly occupied d z2 of Cu II can be considered as a potential ferromagnetic exchange.…”

Itinerant ferromagnetism in a spin-fermion model for diluted spin systems

“…Although ferromagnetic Heisenberg model is explored to understand itinerant ferromagnetism 18 but the real difficulty lies in arriving at the effective Hamiltonian of an interacting spin * kalpataru.pradhan@saha.ac.in system with negative exchange coupling 16 . Ferromagnetic kinetic exchange between localized spins that arises from an interplay of spin and orbital degrees of freedom is relatively rare 19 .…”