Theoretical Study on the Negative Thermal Expansion Perovskite LaCu₃Fe₄O₁₂: Pressure-Triggered Transition of Magnetism, Charge, and Spin State

Abstract

The A-site ordered negative thermal expansion material LaCuFeO (LaCFO) was comprehensively investigated by using first-principles calculations. A pressure-triggered crystal structural phase transition from space group Im3̅ (No. 204) to Pn3̅ (No. 201) and magnetic transformation from a G-type antiferromagnetic (G_AFM) ground state to ferrimagnetic (FerriM) coupling were observed in LaCFO via gradual compression of the equilibrium volume. Correspondingly, the Fe-Cu intersite charge transfer from Fe to Cu 3d orbital, expressed as 4Fe + 3Cu → 4Fe + 3Cu, was simulated along with the magnetic phase transformation from the G_AFM configuration to the FerriM state. Intriguingly, the Fe charge disproportionation, formulated as 8Fe → 5Fe + 3Fe, appeared and was attributed to the strong hybridization between Fe 3d and O 2p orbitals in the FerriM state when the volumes were substantially compressed up to less than or equal to 80%V. Meanwhile, the external hydrostatic pressure also leads to a spin flip from a high-spin Fe antiferromagnetically arranged LaCuFeO Mott insulator at low pressure and goes through a FerriM LaCuFeO half-metal to a low-spin FerriM coupled LaCuFeFeO metal at high pressure. Therefore, the crossover from high spin to low spin is responsible for the charge disproportionation in LaCFO. Essentially, the charge transfer and spin flip originate from the discontinuous changes of metal-oxygen bond lengths and angles in the compressed atomic structure. Finally, the negative thermal expansion behavior and mechanism of LaCFO were theoretically examined and clearly revealed.

Understanding the effect of water transport on the thermal expansion properties of the perovskites BaFe0.6Co0.3Nb0.1O3−δ and BaCo0.7Yb0.2Bi0.1O3−δ

“…The most frequently reported ones are phase transitions (ice/water), electronic valence transitions [19][20][21], ferroelectric ordering [22][23][24], contraction of zeolites (siliceous or ZrW 2 O 8 ) by changing in bridging M-O-M bond angles [25][26][27] or orbital and magnetic ordering [28]. While there have been some reports of perovskite materials with NTE during the last three decades [29][30][31][32][33], such observations are unusual as perovskites in the form ABO 3 generally do not exhibit NTE properties [30]. Another factor that is important for thermal expansion characteristics, particularly for perovskite systems in SOC operation, is the changes to the composition.…”

High-Temperature Ferrimagnetic Half Metallicity with Wide Spin-up Energy Gap in NaCu3Fe2Os2O12

“…In 1983, de Groot et al reported the first half metal . Since then, a wide variety of half-metallic magnets with different crystal structures were proposed in both experiment and theory. − However, it is still a big challenge to search for high-performance half metals with potential application near room temperature.…”

Eu–Mn Charge Transfer and the Strong Charge–Spin–Electronic Coupling Behavior in EuMnO3

“…In this work, first-principles calculations based on the DFT method were performed as implemented in the Vienna Ab initio Simulation Package (VASP) within the projector-augmented plane wave (PAW) method and WIEN2k code based on the full potential linearized augmented-plane-wave (FL-LAPW) method. − We performed structural optimization in the former code and calculated electronic as well as magnetic characteristics in the latter one, which was proved to be a conventional and effective way to deal with the systems involving f-electrons and/or magnetic characteristics. − In both packages, we employed the exchange–correlation functional given by generalized gradient approximation (GGA) in the form of Perdew, Burke and Ernzerhof revised for solids (PBEsol) . Hubbard U correction was applied to Eu 4f states and Mn 3d states .…”