Permanent Electride Magnets Induced by Quasi-Atomic Non-Nucleus-Bound Electrons

Interstitial quasi-atomic electrons (IQEs) in the quantized energy levels of positively charged cavities possess a substantial own magnetic moment and control the magnetism of crystalline electrides depending on the interaction with surrounding cations. However, weak spin-orbit coupling and gentle exchange interaction restricted by the IQEs preclude a large magnetic anisotropic, remaining a challenge for a hard magnetism. It is reported that 2D [Re₂C]²⁺·2e⁻ electrides (Re = Er, Ho, Dy, and Tb) show the permanent magnetism in a ferrimagnetic ground state, mimicking the ferrites composed of magnetic sublattices with different spin polarizations. Magnetic interaction between Re-spin lattice and IQE-spin lattice in the [Re₂C]²⁺·2e⁻ electrides results in a large magnetocrystalline anisotropy and high coercivity, giving a maximum energy product of 15 MGOe. It is demonstrated that the spontaneous breaking of magnetic IQE-sublattice through substitution with paramagnetic elements produces a crossover into an antiferromagnetic spin ordering of Re-sublattice, implying that the magnetic sublattice of IQEs drives the permanent magnetism.