PbMO3 (M = 3d transition metals) family shows systematic variations in charge distribution and intriguing physical properties due to its delicate energy balance between Pb 6s and transition metal 3d orbitals. However, the detailed structure and physical properties of PbFeO3 remain unclear. Herein, we reveal that PbFeO3 crystallizes into an unusual 2ap × 6ap × 2ap orthorhombic perovskite super unit cell with space group Cmcm. The distinctive crystal construction and valence distribution of Pb2+0.5Pb4+0.5FeO3 lead to a long range charge ordering of the -A-B-B- type of the layers with two different oxidation states of Pb (Pb2+ and Pb4+) in them. A weak ferromagnetic transition with canted antiferromagnetic spins along the a-axis is found to occur at 600 K. In addition, decreasing the temperature causes a spin reorientation transition towards a collinear antiferromagnetic structure with spin moments along the b-axis near 418 K. Our theoretical investigations reveal that the peculiar charge ordering of Pb generates two Fe3+ magnetic sublattices with competing anisotropic energies, giving rise to the spin reorientation at such a high critical temperature.

Spin state transition and intermetallic charge transfer can essentially change material structural and physical properties with a fashion of excluding external chemical doping. However, these two effects have rarely been found to occur sequentially in a specific material. In this article, we show the realization of these two phenomena in a perovskite oxide PbCoO3 with a simple ABO3 composition under high pressure. PbCoO3 possesses a peculiar A-and B-site ordered charge distribution Pb 2+ Pb 4+ 3Co 2+ 2Co 3+ 2O12 with insulating behavior at ambient conditions. The high spin Co 2+ gradually changes to low spin with increasing pressure up to about 15 GPa, leading to the anomalous increase of resistance magnitude. Between 15 GPa and 30 GPa, the intermetallic charge transfer occurs between Pb 4+ and Co 2+ cations. The accumulated charge-transfer effect triggers a metal-insulator transition as well as a first-order structural phase transition toward a Tetra.-I phase at the onset of ~20 GPa near room temperature. On further compression over 30 GPa, the charge transfer completes, giving rise to another first-order structural transformation toward a Tetra.-II phase and the reentrant electrical insulating behavior.

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Half metals, in which one spin channel is conducting while the other is insulating with an energy gap, are theoretically considered to comprise 100% spin‐polarized conducting electrons, and thus have promising applications in high‐efficiency magnetic sensors, computer memory, magnetic recording, and so on. However, for practical applications, a high Curie temperature combined with a wide spin energy gap and large magnetization is required. Realizing such a high‐performance combination is a key challenge. Herein, a novel A‐ and B‐site ordered quadruple perovskite oxide LaCu3Fe2Re2O12 with the charge format of Cu2+/Fe3+/Re4.5+ is reported. The strong Cu2+(↑)Fe3+(↑)Re4.5+(↓) spin interactions lead to a ferrimagnetic Curie temperature as high as 710 K, which is the reported record in perovskite‐type half metals thus far. The saturated magnetic moment determined at 300 K is 7.0 μB f.u.−1 and further increases to 8.0 μB f.u.−1 at 2 K. First‐principles calculations reveal a half‐metallic nature with a spin‐down conducting band while a spin‐up insulating band with a large energy gap up to 2.27 eV. The currently unprecedented realization of record Curie temperature coupling with the wide energy gap and large moment in LaCu3Fe2Re2O12 opens a way for potential applications in advanced spintronic devices at/above room temperature.

A 4H-type BaMnO 3 single crystal was prepared by combining the floating zone method with high-pressure treatment at 5 GPa and 1023 K. The crystal crystallizes to a hexagonal structure with space group P6 3 /mmc and lattice parameters a = 5.63723(5) Å and c = 9.22355(8) Å. In this structure, face-sharing MnO 6 octahedral dimers connect with each other by corner O atoms along the c-axis direction, forming an -A-B-A-C-type 4H arrangement. A long-range antiferromagnetic (AFM) phase transition is found to occur at T N ≈ 263 K. When the synthesis pressure increases to 20 GPa, a new polymorphic phase is obtained. This higher-pressure phase still possesses the hexagonal P6 3 /mmc symmetry, but the lattice parameters change to be a = 5.61349(2) Å and c = 13.66690(9) Å with a unit cell volume reduction of 2.05%. In this new phase, the c-axis MnO 6 dimers are separated by MnO 6 octahedral layers in the ab plane, forming an -A−B-C-A-C-B-type 6H structure. The 6H phase exhibits two long-range AFM orderings at T N1 ≈ 220 K and T N2 ≈ 25 K, respectively. The different magnetic properties are discussed on the basis of the detailed structural constitutions of 4H-and 6H-BaMnO 3 .

An A- and B-site ordered quadruple perovskite oxide LaCu3Co2Re2O12 was synthesized at 9 GPa and 1323 K. The compound possesses a Pn-3 space group, where both A and B sites are orderly occupied by different cations with a nearly 100% degree of order. Bond valence sum calculations and x-ray absorption spectroscopy confirm the charge distribution to be LaCu2+3Co2+2Re5.5+2O12. A ferrimagnetic phase transition is found to occur around 150 K due to the Cu2+(↑)-Co2+(↑)-Re5.5+(↓) spin coupling found by x-ray magnetic circular dichroism at Cu-, Co-, and Re-L2,3 edges. The magnetoresistance effects as well as the first-principle calculations indicate the half-metallic nature for LaCu3Co2Re2O12 with a wider energy gap at the up-spin channel and a conducting band at the down-spin channel.

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A new 3d–5d hybridization oxide, CaCu3Mn2Os2O12 (CCMOO), was prepared by high-pressure and high-temperature synthesis methods. The compound crystallizes to an A-site-ordered but B-site-disordered quadruple perovskite structure with a space group of Im3̅ (No. 204). The charge states of the transition metals are determined to be Cu2+/Mn3.5+/Os4.5+ by X-ray absorption spectroscopy. Although most B-site-disordered perovskites possess lower spin-ordering temperatures or even nonmagnetic transitions, the current CCMOO displays a long-range ferrimagnetic phase transition with a critical temperature as high as ∼280 K. Moreover, a large saturated magnetic moment is found to occur [7.8 μB/formula units (f.u.) at 2 K]. X-ray magnetic circular dichroism shows a Cu2+(↑)­Mn3.5+(↑)­Os4.5+(↓) ferrimagnetic coupling. The corner-sharing Mn/OsO6 octahedra with mixed Mn and Os charge states make the compound metallic in electrical transport, in agreement with a specific heat fitting at low temperature. This work provides a rare example with high spin-ordering temperature and a large magnetic moment in B-site-disordered 3d–5d hybridization perovskite oxides.