Effects of Isovalent Substitution in the Manganese Sublattice on Magnetic, Thermal, and Structural Properties of BiMnO₃: BiMn_1-<i>_x</i>M<i>_x</i>O₃ (M = Al, Sc, Cr, Fe, Ga; 0 ≤ <i>x</i> ≤ 0.2)

Solid solutions BiMn1-xMxO3 with M = Al, Sc, Cr, Fe, and Ga and 0 ≤ x ≤ 0.2 were prepared at a high pressure of 6 GPa and 1333−1453 K, and their magnetic, thermal, and structural properties were investigated. The orbital-ordered monoclinic phase of BiMnO3 (phase I) is destroyed by a small percentage of substitution. The M elements can be classified by their ability to destroy phase I in the sequence Ga (x ≈ 0.08) ≈ Fe (x ≈ 0.08) x ≈ 0.04) ≈ Al (x ≈ 0.04) x ≈ 0.02), where phase I is most stable for Ga substitution (up to x ≈ 0.08) and less stable for Sc substitution (up to x ≈ 0.02). The orbital-disordered high-temperature monoclinic phase of BiMnO3 (phase II) is stabilized with larger x. In all cases, a compositional range was found where phases I and II coexist at room temperature. In phase I, the effect of substitution on the ferromagnetic transition temperature is weak (e.g., TC = 102 K for BiMnO3 and TC = 99 K for BiMn0.95Ga0.05O3), but there is a drastic effect on the orbital ordering temperature (e.g., TOO = 474 K for BiMnO3 and TOO = 412 K for BiMn0.95Ga0.05O3). Magnetic susceptibilities of phase I are typical for ferromagnets while, in phase II, ferromagnetic cluster-glass-like behavior is observed. The magnetic transition temperature of phase II (e.g., TC = 70 K for BiMn0.8Ga0.2O3) exhibits a sudden drop compared with that of phase I. The effect of substitution on the structural monoclinic-to-orthorhombic transition is different depending on M (e.g., Tstr = 768 K for BiMnO3, Tstr = 800 K for BiMn0.95Ga0.05O3, and Tstr = 738 K for BiMn0.85Cr0.15O3)

Effects of Oxygen Content on Bi₃Mn₃O_11+δ: From 45 K Antiferromagnetism to Room-Temperature True Ferromagnetism

The effects of oxygen content on the structural, physical, and chemical properties of Bi3Mn3O11 with KSbO3-type structure have been investigated. It was found that the oxygen content in Bi3Mn3O11+δ can vary over a wide δ range, keeping the same cubic structure (space group Pn3̅, a = 9.12172(5) Å for δ = −0.5, a = 9.13784(8) Å for δ = 0, and a = 9.09863(7) Å for δ = 0.6) and semiconducting properties of the material. At the same time, magnetic properties change from true antiferromagnetic with TN = 45 K for δ = −0.5 to true ferromagnetic with TC = 307 K for δ = +0.6. Bi3Mn3O11 (δ = 0) shows ferrimagnetic-like properties with TC = 150 K and features typical for a re-entrant spin-glass below 30 K. Noticeable changes of the magnetic transition temperature and magnetism in Bi3Mn3O11+δ with δ can be compared with changes of the magnetic and electronic properties of LaMnO3+δ, BiMnO3+δ, high-temperature copper superconductors (e.g., YBa2Cu3O7+δ), and other cuprates. Bi3Mn3O11.6 shows a new record high TC among insulating/semiconducting true ferromagnets. Our results demonstrate that the oxygen content can vary for the same cation composition in KSbO3-type materials, and the oxygen content can be increased up to BiMnO3.867 (Bi3Mn3O11.6)

Effects of Oxygen Content on Bi₃Mn₃O_11+δ: From 45 K Antiferromagnetism to Room-Temperature True Ferromagnetism

The effects of oxygen content on the structural, physical, and chemical properties of Bi3Mn3O11 with KSbO3-type structure have been investigated. It was found that the oxygen content in Bi3Mn3O11+δ can vary over a wide δ range, keeping the same cubic structure (space group Pn3̅, a = 9.12172(5) Å for δ = −0.5, a = 9.13784(8) Å for δ = 0, and a = 9.09863(7) Å for δ = 0.6) and semiconducting properties of the material. At the same time, magnetic properties change from true antiferromagnetic with TN = 45 K for δ = −0.5 to true ferromagnetic with TC = 307 K for δ = +0.6. Bi3Mn3O11 (δ = 0) shows ferrimagnetic-like properties with TC = 150 K and features typical for a re-entrant spin-glass below 30 K. Noticeable changes of the magnetic transition temperature and magnetism in Bi3Mn3O11+δ with δ can be compared with changes of the magnetic and electronic properties of LaMnO3+δ, BiMnO3+δ, high-temperature copper superconductors (e.g., YBa2Cu3O7+δ), and other cuprates. Bi3Mn3O11.6 shows a new record high TC among insulating/semiconducting true ferromagnets. Our results demonstrate that the oxygen content can vary for the same cation composition in KSbO3-type materials, and the oxygen content can be increased up to BiMnO3.867 (Bi3Mn3O11.6)

Effects of Isovalent Substitution in the Manganese Sublattice on Magnetic, Thermal, and Structural Properties of BiMnO₃: BiMn_1-<i>_x</i>M<i>_x</i>O₃ (M = Al, Sc, Cr, Fe, Ga; 0 ≤ <i>x</i> ≤ 0.2)

Solid solutions BiMn1-xMxO3 with M = Al, Sc, Cr, Fe, and Ga and 0 ≤ x ≤ 0.2 were prepared at a high pressure of 6 GPa and 1333−1453 K, and their magnetic, thermal, and structural properties were investigated. The orbital-ordered monoclinic phase of BiMnO3 (phase I) is destroyed by a small percentage of substitution. The M elements can be classified by their ability to destroy phase I in the sequence Ga (x ≈ 0.08) ≈ Fe (x ≈ 0.08) x ≈ 0.04) ≈ Al (x ≈ 0.04) x ≈ 0.02), where phase I is most stable for Ga substitution (up to x ≈ 0.08) and less stable for Sc substitution (up to x ≈ 0.02). The orbital-disordered high-temperature monoclinic phase of BiMnO3 (phase II) is stabilized with larger x. In all cases, a compositional range was found where phases I and II coexist at room temperature. In phase I, the effect of substitution on the ferromagnetic transition temperature is weak (e.g., TC = 102 K for BiMnO3 and TC = 99 K for BiMn0.95Ga0.05O3), but there is a drastic effect on the orbital ordering temperature (e.g., TOO = 474 K for BiMnO3 and TOO = 412 K for BiMn0.95Ga0.05O3). Magnetic susceptibilities of phase I are typical for ferromagnets while, in phase II, ferromagnetic cluster-glass-like behavior is observed. The magnetic transition temperature of phase II (e.g., TC = 70 K for BiMn0.8Ga0.2O3) exhibits a sudden drop compared with that of phase I. The effect of substitution on the structural monoclinic-to-orthorhombic transition is different depending on M (e.g., Tstr = 768 K for BiMnO3, Tstr = 800 K for BiMn0.95Ga0.05O3, and Tstr = 738 K for BiMn0.85Cr0.15O3)

Magnetic Properties of BiMnO₃ Studied with Dc and Ac Magnetization and Specific Heat

Magnetic and specific heat measurements were performed in a single-phased powder BiMnO3 sample prepared at 6 GPa and 1383 K. The imaginary part of the ac susceptibilities showed strong frequency dependence below the ferromagnetic Curie temperature of 98 K. The relaxation measurements revealed time-dependent magnetic properties below 98 K. These data indicate the appearance of a “spin-glass-like” state in BiMnO3. Specific heat measurements showed the existence of ferromagnetic spin waves. However, no simple term Cm ∝ T3/2 was found indicating an unconventional behavior of the magnetic specific heat. The Debye temperature was estimated to be 410 K using isostructural compounds BiScO3 and BiCrO3

Effects of Oxygen Content on Bi₃Mn₃O_11+δ: From 45 K Antiferromagnetism to Room-Temperature True Ferromagnetism

The effects of oxygen content on the structural, physical, and chemical properties of Bi3Mn3O11 with KSbO3-type structure have been investigated. It was found that the oxygen content in Bi3Mn3O11+δ can vary over a wide δ range, keeping the same cubic structure (space group Pn3̅, a = 9.12172(5) Å for δ = −0.5, a = 9.13784(8) Å for δ = 0, and a = 9.09863(7) Å for δ = 0.6) and semiconducting properties of the material. At the same time, magnetic properties change from true antiferromagnetic with TN = 45 K for δ = −0.5 to true ferromagnetic with TC = 307 K for δ = +0.6. Bi3Mn3O11 (δ = 0) shows ferrimagnetic-like properties with TC = 150 K and features typical for a re-entrant spin-glass below 30 K. Noticeable changes of the magnetic transition temperature and magnetism in Bi3Mn3O11+δ with δ can be compared with changes of the magnetic and electronic properties of LaMnO3+δ, BiMnO3+δ, high-temperature copper superconductors (e.g., YBa2Cu3O7+δ), and other cuprates. Bi3Mn3O11.6 shows a new record high TC among insulating/semiconducting true ferromagnets. Our results demonstrate that the oxygen content can vary for the same cation composition in KSbO3-type materials, and the oxygen content can be increased up to BiMnO3.867 (Bi3Mn3O11.6)

Bi₃Mn₃O₁₁: A New KSbO₃-Type Random Ferrimagnet with High <i>T</i>_C

Bi3Mn3O11: A New KSbO3-Type Random Ferrimagnet with High TC</sub

Crystal Structure and Magnetic Properties of the Trilayered Perovskite Sr₄Rh₃O₁₀: A New Member of the Strontium Rhodate Family

The trilayered perovskite Sr4Rh3O10 is reported for the first time. High-pressure and high-temperature heating (6 GPa and 1500 °C) brought about successful preparation of a polycrystalline sample of the expected member at n = 3 of Srn+1RhnO3n+1. Neutron-diffraction studies revealed the orthorhombic crystal structure (Pbam) at room temperature and 3.4 K. Local structure distortions rotationally tilt the RhO6 octahedra ∼12° in the perovskite-based blocks along the c-axis, and approximately a 20% disorder was found in the sequence of the alternating rotational tilt. The sample was also investigated by measurements of specific heat, thermopower, magnetic susceptibility, and electrical resistivity. The data clearly revealed enhanced paramagnetism and electrically conducting character, which reflected the nature of the correlated 4d5-electrons of Rh4+. However, no clear signs of magnetic and electrical transitions were observed above 2 K and below 70 kOe, providing a remarkable contrast to the rich electronic phenomena for the significantly relevant ruthenate Sr4Ru3O10

Perovskite, LiNbO₃, Corundum, and Hexagonal Polymorphs of (In_1–<i>x</i>M_<i>x</i>)MO₃

LiNbO3 (LN), corundum (cor), and hexagonal (hex) phases of (In1–xMx)MO3 (x = 0.143; M = Fe0.5Mn0.5) were prepared. Their crystal structures were investigated with synchrotron X-ray powder diffraction, and their properties were studied by differential thermal analysis, magnetic measurements, and Mössbauer spectroscopy. The LN-phase was prepared at high pressure of 6 GPa and 1770 K; it crystallizes in space group R3c with a = 5.25054(7) Å, c = 13.96084(17) Å, and has a long-range antiferromagnetic ordering near TN = 270 K. The cor- and hex-phases were obtained at ambient pressure by heating the LN-phase in air up to 870 and 1220 K, respectively. The cor-phase crystallizes in space group R-3c with a = 5.25047(10) Å, c = 14.0750(2) Å, and the hex-phase in space group P63/mmc with a = 3.34340(18) Å, c = 11.8734(5) Å. TN of the cor-phase is about 200 K, and TN of the hex-phase is about 140 K. During irreversible transformations of LN-(In1–xMx)MO3 with the (partial) cation ordering, the In3+, Mn3+, and Fe3+ cations become completely disordered in one crystallographic site of the corundum structure, and then they are (partially) ordered again in the hex-phase. LN-(In1–xMx)MO3 exhibits a reversible transformation to a perovskite GdFeO3-type structure (space group Pnma; a = 5.2946(3) Å, b = 7.5339(4) Å, c = 5.0739(2) Å at 10.3 GPa) at room temperature and pressure of about 5 GPa

Magnetic Properties of Bulk BiCrO₃ Studied with dc and ac Magnetization and Specific Heat

Single-phased powder BiCrO3 sample was prepared at 6 GPa and 1653 K. Its magnetic properties were investigated by dc/ac magnetization, magnetic relaxation, and specific heat measurements. Four anomalies of magnetic origin were found near 40, 75, 109, and 111 K. The long-range antiferromagnetic order with weak ferromagnetism occurs at TN = 109 K. The ac susceptibilities showed that the transition near TN is a two-step transition. Additional frequency-independent broad anomalies were observed on the real part of the ac susceptibilities near 75 K, likely, caused by the change in the magnetic easy axis. The dc magnetic susceptibilities also had anomalies at 75 K, and the isothermal magnetization curves and relaxation curves changed their behavior below 75 K. Below 40 K, frequency-dependent anomalies with very large temperature shifts were observed on both the real and imaginary parts of the ac susceptibilities. The monoclinic-to-orthorhombic structural phase transition near 420 K was investigated by magnetization and differential scanning calorimetry measurements