High-Pressure Synthesis of Semiconducting PbCu3Mn4O12 with Near-Room-Temperature Ferrimagnetic Order.

A transition-metal oxide of PbCu3Mn4O12 was prepared at 1523 K and 10 GPa. An A-site-ordered quadruple perovskite structure with the space group Im3̅ is assigned for this compound. Based on bond-valence-sum calculations and X-ray absorption spectroscopy, the charge combination is determined to be PbCu32+Mn44+O12. Due to Cu2+(↑)-Mn4+(↓) antiferromagnetic coupling, a near-room-temperature ferrimagnetic phase transition is observed at approximately 287 K. PbCu3Mn4O12 exhibits a semiconducting electric transport property with the energy band gap Eg ≈ 0.2 eV. In addition, considerable low-field magnetoresistance effects are observed at lower temperatures. This study provides an intrinsic near-room-temperature ferrimagnetic semiconductor that exhibits potential applications in next-generation spintronic devices.

Exceptional Magnetocaloric Responses in a Gadolinium Silicate with Strongly Correlated Spin Disorder for Sub-Kelvin Magnetic Cooling.

The development of magnetocaloric materials with a significantly enhanced volumetric cooling capability is highly desirable for the application of adiabatic demagnetization refrigerators in confined spatial environments. Here, the thermodynamic characteristics of a magnetically frustrated spin-7/2 Gd9.33[SiO4]6O2 is presented, which exhibits strongly correlated spin disorder below ≈1.5 K. A quantitative model is proposed to describe the magnetization results by incorporating nearest-neighbor Heisenberg antiferromagnetic and dipolar interactions. Remarkably, the recorded magnetocaloric responses are unprecedentedly large and applicable below 1.0 K. It is proposed that the S = 7/2 spin liquids serve as versatile platforms for investigating high-performance magnetocaloric materials in the sub-kelvin regime, particularly those exhibiting a superior cooling power per unit volume.

High-Pressure Synthesis of Quadruple Perovskite Oxide CaCu3Cr2Re2O12 with a High Ferrimagnetic Curie Temperature.

An AA'3B2B'2O12-type quadruple perovskite oxide of CaCu3Cr2Re2O12 was synthesized at 18 GPa and 1373 K. Both an A- and B-site ordered quadruple perovskite crystal structure was observed, with the space group Pn-3. The valence states are verified to be CaCu32+Cr23+Re25+O12 by bond valence sum calculations and synchrotron X-ray absorption spectroscopy. The spin interaction among Cu2+, Cr3+, and Re5+ generates a ferrimagnetic transition with the Curie temperature (TC) at about 360 K. Moreover, electric transport properties and specific heat data suggest the presence of a half-metallic feature for this compound. The present study provides a promising quadruple perovskite oxide with above-room-temperature ferrimagnetism and possible half-metallic properties, which shows potential in the usage of spintronic devices.

Robust Crystal Phase Separation with Distinct Charge, Orbital, and Spin Orders in AgMn7O12.

An AA'3B4O12-type A-site-ordered quadruple perovskite oxide AgMn7O12 was prepared by high-pressure and high-temperature methods. At room temperature, the compound crystallizes into a cubic Im3̅ symmetry with a charge distribution of AgMn33+Mn43.5+O12. With the temperature decreasing to TCO,OO ≈ 180 K, the compound undergoes a structural phase transition toward a monoclinic C2/m symmetry, giving rise to a B-site charge- and orbital-ordered AgMn33+Mn23+Mn24+O12 phase. Moreover, this charge-/orbital-ordered main phase coexists with the initial cubic AgMn33+Mn43.5+O12 phase in the wide temperature range we measured. The charge-/orbital-ordered phase shows two antiferromagnetic phase transitions near 125 and 90 K, respectively. Short-range ferromagnetic correlations are found to occur for the initial B-site mixed cubic phase around 35 K. Because of the robust phase separation, considerable magnetoresistance effects are observed below TCO,OO in AgMn7O12.

Antiferroelectricity-Induced Negative Thermal Expansion in Double Perovskite Pb2 CoMoO6.

Materials with negative thermal expansion (NTE) attract significant research attention owing to their unique physical properties and promising applications. Although ferroelectric phase transitions leading to NTE are widely investigated, information on antiferroelectricity-induced NTE remains limited. In this study, single-crystal and polycrystalline Pb2 CoMoO6 samples are prepared at high pressure and temperature conditions. The compound crystallizes into an antiferroelectric Pnma orthorhombic double perovskite structure at room temperature owing to the opposite displacements dominated by Pb2+ ions. With increasing temperature to 400 K, a structural phase transition to cubic Fm-3m paraelectric phase occurs, accompanied by a sharp volume contraction of 0.41%. This is the first report of an antiferroelectric-to-paraelectric transition-induced NTE in Pb2 CoMoO6 . Moreover, the compound also exhibits remarkable NTE with an average volumetric coefficient of thermal expansion αV = -1.33 × 10-5 K-1 in a wide temperature range of 30-420 K. The as-prepared Pb2 CoMoO6 thus serves as a prototype material system for studying antiferroelectricity-induced NTE.

CaCu3Mn2Te2O12: An Intrinsic Ferrimagnetic Insulator Prepared Under High Pressure.

CaCu3Mn2Te2O12 was synthesized using high-temperature and high-pressure conditions. The compound possesses an A- and B site ordered quadruple perovskite structure in Pn3̅ symmetry with the charge combination of CaCu32+Mn22+Te26+O12. A ferrimagnetic phase transition originating from the antiferromagnetic interaction between A' site Cu2+ and B site Mn2+ ions is found to occur at TC ≈ 100 K. CaCu3Mn2Te2O12 also shows insulating electric conductivity. Optical measurement demonstrates the energy bandgap to be about 1.9 eV, in agreement with the high B site degree of chemical order between Mn2+ and Te6+. The first-principles theoretical calculations confirm the Cu2+(↓)-Mn2+(↑) ferrimagnetic coupling as well as the insulating nature with an up-spin direct bandgap. The current CaCu3Mn2Te2O12 provides an intriguing example of an intrinsic ferrimagnetic insulator with promising applications in advanced spintronic devices.

High-Pressure-Stabilized Post-Spinel Phase of CdFe2O4 with Distinct Magnetism from Its Ambient-Pressure Spinel Phase.

α-CdFe2O4 stabilizes its normal spinel structure due to the covalent Cd-O bond, in which all the connections between adjacent FeO6 octahedral are edge-shared, forming a typical geometrically frustrated Fe3+ magnetic lattice. As the high-pressure methods were utilized, the post-spinel phase ß-CdFe2O4 with a CaFe2O4-type structure was synthesized at 8 GPa and 1373 K. The new polymorph has an orthorhombic structure with the space group Pnma and an 11.5% higher density than that of its normal spinel polymorph (α-CdFe2O4) synthesized at ambient conditions. The edge-shared FeO6 octahedra form zigzag S = 5/2 spin ladders along the b-axis dominating its low-dimensional magnetic properties at high temperatures and a long-range antiferromagnetic ordering with a high Néel temperature of TN1 = 350 K. Further, the rearrangement of magnetic ordering was found to occur around TN2 = 265 K, below which the competition of two phases or several couplings induce complex antiferromagnetic behaviors.

High-pressure single crystal growth and magnetoelectric properties of CdMn7O12.

The concurrent presence of large electric polarization and strong magnetoelectric coupling is quite desirable for potential applications of multiferroics. In this paper, we report the growth of CdMn7O12single crystals by flux method under a high pressure of 8 GPa for the first time. An antiferromagnetic (AFM) order with a polar magnetic point group is found to occur at the onset temperature ofTN1= 88 K (AFM1 phase). As a consequence, the pyroelectric current emerges atTN1and gradually increases and reaches its maximum atTset= 63 K, at which the AFM1 phase finally settles down. BelowTset, CdMn7O12single crystal exhibits a large ferroelectric polarization up to 2640µC m-2. Moreover, the spin-induced electric polarization can be readily tuned by applying magnetic fields, giving rise to considerable magnetoelectric coupling effects. Thus, the current CdMn7O12single crystal acts as a rare multiferroic system where both large polarization and strong magnetoelectric coupling merge concurrently.

Strong Magnetocaloric Coupling in Oxyorthosilicate with Dense Gd3+ Spins.

Searching for working refrigerant materials is the key element in the design of magnetic cooling devices. Herein, we report on the thermodynamic and magnetocaloric parameters of an X1 phase oxyorthosilicate, Gd2SiO5, by field-dependent static magnetization and specific heat measurements. An overall correlation strength of |J|S2 ≈ 3.4 K is derived via the mean-field estimate, with antiferromagnetic correlations between the ferromagnetically coupled Gd-Gd layers. The magnetic entropy change -ΔSm is quite impressive, reaches 0.40 J K-1 cm-3 (58.5 J K-1 kg-1) at T = 2.7 K, with the largest adiabatic temperature change Tad = 23.2 K for a field change of 8.9 T. At T = 20 K, the lattice entropy SL is small enough compared to the magnetic entropy Sm, Sm/SL = 21.3, which warrants its potential in 2 -20 K cryocoolers with both the Stirling and Carnot cycles. Though with relatively large exchange interactions, the layered A-type spin arrangement ultimately enhances the magnetocaloric coupling, raising the possibilities of designing magnetic refrigerants with a high ratio of cooling capacity to volume.

Immunization with a Prefusion SARS-CoV-2 Spike Protein Vaccine (RBMRNA-176) Protects against Viral Challenge in Mice and Nonhuman Primates.

There is an urgent need for a broad-spectrum and protective vaccine due to the emergence and rapid spreading of more contagious SARS-CoV-2 strains. We report the development of RBMRNA-176, a pseudouridine (Ψ) nucleoside-modified mRNA-LNP vaccine encoding pre-fusion stabilized trimeric SARS-CoV-2 spike protein ectodomain, and evaluate its immunogenicity and protection against virus challenge in mice and nonhuman primates. A prime-boost immunization with RBMRNA-176 at intervals of 21 days resulted in high IgG titers (over 1:819,000 endpoint dilution) and a CD4+ Th1-biased immune response in mice. RBMRNA-176 vaccination induced pseudovirus-neutralizing antibodies with IC50 ranging from 1:1020 to 1:2894 against SARS-CoV-2 spike pseudotyped wild-type and variant viruses, including Alpha, Beta, Gamma, and Kappa. Moreover, significant control of viral replication and histopathology in lungs was observed in vaccinated mice. In nonhuman primates, a boost given by RBMRNA-176 on day 21 after the prime induced a persistent and sustained IgG response. RBMRNA-176 vaccination also protected macaques against upper and lower respiratory tract infection, as well as lung injury. Altogether, these findings support RBMRNA-176 as a vaccine candidate for prevention of COVID-19.