Compensated ferrimagnetic Heusler alloys: A search for the forgotten Neel's L -type ferrimagnet

In his groundbreaking work on the theory of ferri- and antiferromagnetism, Néel proposed the existence of ferrimagnets with zero net magnetization. These L -type ferrimagnets were later termed fully compensated. This study focuses on L -type ferrimagnets, particularly Heusler alloys based on vanadium (V), manganese (Mn), iron (Fe), and cobalt (Co). First-principles calculations reveal that these ferrimagnets exhibit anomalous temperature dependence, differing from antiferromagnets. Spin dynamics calculations, based on the calculated exchange coupling coefficients, show that this behavior stems from the ferrimagnets' inequivalent magnetic sublattices, which have distinct exchange interactions. The temperature dependence of the magnetic properties is analyzed through a comparison of the first-principles calculations and Néel's molecular field theory, extended to include Heusler compounds. In addition to exhibiting compensated ferrimagnetic behavior, examining the electronic structure using the Bloch spectral function shows that the investigated Heusler alloys are half-metals which have a full spin polarization at the Fermi energy. The combination of complete magnetic compensation and half-metallicity makes these alloys interesting for fundamental research and spintronics applications because their zero net magnetization minimizes stray fields while retaining half-metallicity.