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A Polycrystalline sample of Pb2NiOsO6 was synthesized by high-pressure (6 GPa) and high-temperature (1575 K) conditions. Pb2NiOsO6 crystallizes in a monoclinic double perovskite structure with a centrosymmetric space group P21/n at room temperature. Pb2NiOsO6 is metallic down to 2 K and shows a single antiferromagnetic (AFM) transition at TN = 58 K. Pb2NiOsO6 is a new example of a metallic and antiferromagnetic oxide with three-dimensional connectivity. Neutron powder diffraction and first-principle calculation studies indicate that both Ni and Os moments are ordered below TN and the antiferromagnetic magnetic order breaks inversion symmetry. This loss of inversion symmetry driven by antiferromagnetic order is unusual in metallic systems and the 3d-5d double-perovskite oxides represent a new class of noncentrosymmetric AFM metallic oxides.

NaOsO3 has recently attracted significant attention for the strong coupling between its electronic band structure and magnetic ordering. Here, we used time-resolved magnetic x-ray diffraction to determine the timescale of the photoinduced antiferromagnetic dynamics in NaOsO3. Our measurements are consistent with a sub-100 fs melting of the antiferromagnetic long-range order that occurs significantly faster than the lattice dynamics as monitored by the transient change in intensity of selected Bragg structural reflections, which instead show a decrease of intensity on a timescale of several ps.

The formation of NaRMn2Ti4O12 compounds (R = rare earth) under high pressure (about 6 GPa) and high temperature (about 1750 K) conditions was studied. Such compounds with R = Sm, Eu, Gd, Dy, Ho, Y ...

Single crystals of a new germanium oxysulfide La4(GeS2O2)3 were grown out of a BaCl2-CaCl2 eutectic flux, and the crystal structure was determined via single-crystal X-ray diffraction. Ivory-white ...

Polycrystalline Sr3OsO6, which is an ordered double-perovskite insulator, is synthesized via solid-state reaction under high-temperature and high-pressure conditions of 1200 °C and 6 GPa. The synth...

Topochemical reactions between CaCrO3 and polyvinylidene difluoride yield the new fluorinated phase CaCrO2.5F0.5, which was characterized by powder synchrotron X-ray diffraction, X-ray photoemission spectroscopy, and magnetic susceptibility measurements. The reaction proceeds via reduced oxide intermediates, CaCrO2.67 and CaCrO2.5, in which CrO6 octahedral and CrO4 tetrahedral layers are stacked in a different manner along the c axis of CaCrO3. These two intermediate phases can be selectively synthesized by the carbothermal reduction with g-C3N4. Both CaCrO3 and CaCrO2.5F0.5 adopt the same orthorhombic space group, Pbnm; however, the fluorinated phase has decreased Cr-O-Cr bond angles as compared to the parent compound in both the ab plane and along the c-direction, which indicates an increased orthorhombic distortion due to the fluorination. While the oxygen vacancies are ordered in both intermediate phases, CaCrO2.67 and CaCrO2.5, a site preference for fluorine in the oxyfluoride phase cannot be confirmed. CaCrO3 and CaCrO2.5F0.5 undergo antiferromagnetic phase transitions involving spin canting, where the fluorination causes the transition temperature to increase from 90 K to 110 K, as a result of the competition between the increased octahedral tilting and the enhancement of superexchange interactions involving Cr3+ ions in the CaCrO2.5F0.5 structure.

ABO3 perovskite materials with small cations at the A site, especially those with ordered cation arrangements, have attracted a great deal of interest because they show unusual physical properties and deviations from the general characteristics of perovskites. In this work, perovskite solid solutions (Lu0.5Mn0.5)(Mn1−xTix)O3 with x = 0.25, 0.50, and 0.75 were synthesized by means of a high-pressure, high-temperature method at approximately 6 GPa and approximately 1550 K. All the samples crystallize in the GdFeO3-type perovskite structure (space group Pnma) and have random distributions of the small Lu3+ and Mn2+ cations at the A site and Mn4+/3+/2+ and Ti4+ cations at the B site, as determined by Rietveld analysis of high-quality synchrotron X-ray powder diffraction data. Lattice parameters are a = 5.4431 Å, b = 7.4358 Å, c = 5.1872 Å (for x = 0.25); a = 5.4872 Å, b = 7.4863 Å, c = 5.2027 Å (for x = 0.50); and a = 5.4772 Å, b = 7.6027 Å, c = 5.2340 Å (for x = 0.75). Despite a significant dilution of the A and B sublattices by non-magnetic Ti4+ cations, the x = 0.25 and 0.50 samples show long-range ferrimagnetic order below TC = 89 K and 36 K, respectively. Mn cations at both A and B sublattices are involved in the long-range magnetic order. The x = 0.75 sample shows a spin-glass transition at TSG = 6 K and a large frustration index of approximately 22. A temperature-independent dielectric constant was observed for x = 0.50 (approximately 32 between 5 and 150 K) and for x = 0.75 (approximately 50 between 5 and 250 K).

Perovskite-type ABO3 oxides show a number of cation-ordered structures, which have significant effects on their properties. The rock-salt-type order is dominant for B cations, and the layered order for A cations. In this work, we prepared a new perovskite-type oxide, Sm2CuMn(MnTi3)O12, with a rare columnar A-site order using a high-pressure, high-temperature method at about 6 GPa and about 1700 K. Its crystal structure was studied with synchrotron powder X-ray diffraction. The compound crystallizes in space group P42/nmc (No. 137) at room temperature with a = 7.53477 Å and c = 7.69788 Å. The magnetic properties of the compound were studied with dc and ac magnetic susceptibility measurements and specific heat. Spin-glass (SG) magnetic properties were found with TSG = 7 K, while specific heat, in the form of Cp/T, showed a strong, very broad anomaly developing below 20 K and peaking at 4 K. The dielectric constant of Sm2CuMn(MnTi3)O12 was nearly frequency and temperature independent between 8 K and 200 K, with a value of about 50. Cu2+ doping drastically modified the magnetic and dielectric properties of Sm2CuMn(MnTi3)O12 in comparison with the parent compound Sm2MnMn(MnTi3)O12, which showed a long-range ferrimagnetic order at 34–40 K. The antisite disorder of Cu2+ and Mn2+ cations between square-planar and octahedral sites was responsible for the SG magnetic properties of Sm2CuMn(MnTi3)O12.

We report magnetic, transport, neutron diffraction, and muon spin rotation data showing that Pb$_2$CoOsO$_6$, a newly synthesized metallic double-perovskite with a centrosymmetric space group at room temperature, exhibits a continuous second-order phase transition at 45 K to a magnetically ordered state with a non-centrosymmetric space group. The absence of inversion symmetry is very uncommon in metals, particularly metallic oxides. In contrast to the recently reported ferroelectric-like structural transition in LiOsO$_3$, the phase transition in Pb$_2$CoOsO$_6$ is driven by a long-range collinear antiferromagnetic order, with propagation vector $\textbf{k} = (\frac{1}{2},0,\frac{1}{2})$, which relieves the frustration associated with the symmetry of themagnetic exchanges. This magnetically-driven loss of inversion symmetry represents a new frontier in the search for novel metallic behavior., 5 pages, 3 figures

A-site-ordered quadruple perovskite CeCu3Cr4O12 was prepared by a high-pressure, high-temperature method at 7.7 GPa and about 1670 K. Its crystal structure was investigated using synchrotron X-ray powder diffraction between 100 and 590 K. In this temperature range, it crystallizes in the parent cubic structure for A-site-ordered quadruple perovskites with space group Im-3. It exhibits a ferrimagnetic transition at TC = 333 K. Very small changes of Cu O and Cr O bond lengths were found at TC, and no changes in Ce O bond lengths. Ce O bond lengths of CeCu3Cr4O12 (about 2.525 A at 290 K) were very close to those of CeCu3Mn4O12 and CeCu3Fe4O12 suggesting the Ce4+ oxidation state and the charge distribution as Ce4+Cu2+3Cr3.5+4O12. No intersite charge transfer or charge disproportionation transitions were found in CeCu3Cr4O12.

High-pressure RMn3O6 manganites (belonging to a family of A-site columnar-ordered quadruple perovskites A2A′A″B4O12, where A′ is a site with a square-planar coordination and A″ is a site with a tetrahedral coordination) are prone to cation non-stoichiometry: they are rare-earth-deficient, R1−xMn3+xO6, for R = Ho, Y, Er, and Tm and manganese-deficient, R1+xMn3−xO6, for R = Gd. Here we investigated their crystal structures using single-crystal X-ray diffraction and synchrotron X-ray powder diffraction at room temperature. We found that the rare-earth deficiency is formed by doping of Mn2+ into the A site: [Er3+1.78Mn2+0.22]A[Mn3+]A′[Mn2+]A′′[Mn3+2]B1[Mn3.61+2]B2O12. The manganese deficiency is realized through doping of a small amount of Gd3+ into the A″ site: [Gd3+2]A[Mn3+]A′[Mn2+0.87Gd3+0.13]A′′[Mn3+2]B1[Mn3.44+2]B2O12. They all crystallize in space group Pmmn with layered charge ordering at the B sites. They are structurally related to CaFeTi2O6. Cation non-stoichiometry is supported by variations of the oxidation states of manganese at one of the B sites.

A new polymorph of the triple perovskite Ba3CuOs2O9, which usually exists in the orthorhombic phase, was synthesized under high-pressure and high-temperature conditions at 6 GPa and 1100 °C. Under the synthetic condition, Ba3CuOs2O9 crystallizes into a hexagonal structure (P63/mmc) with a = 5.75178(1) A and c = 14.1832(1) A, and undergoes a 1.36% increment in density, compared to that of the orthorhombic phase. Although Ba3CuOs2O9 maintains its 6 H perovskite-type structure, the distribution of Cu and Os atoms are dramatically altered; (Cu)4a(Os,Os)8f transits to (Os)2a(Cu,Os)4f ordering over the corner- and face-sharing sites, respectively. The hexagonal Ba3CuOs2O9 exhibits a ferrimagnetic transition at 290 K, which is in stark contrast to the antiferromagnetic transition at 47 K exhibited by the orthorhombic Ba3CuOs2O9. The enhanced transition temperature is most likely due to the strongly antiferromagnetic Os5+–O–Os5+ bonds and the moderately antiferromagnetic Os5+–O–Cu2+ bonds, the angles of which are both approximately 180°. The 290 K ferrimagnetic transition temperature is the highest reported for triple-perovskite osmium oxides. Besides, the coercive field is greater than 70 kOe at 5 K, which is remarkable among the coercive fields of magnetic oxides.

We have used muon spin rotation and relaxation (μSR) and 23Na nuclear magnetic resonance (NMR) spectroscopic methods in the NaOsO3 antiferromagnetic phase to determine the temperature evolution of the magnetic order parameter and the role of the magnetic fluctuations at the Néel temperature. Additionally, we performed muon spin relaxation measurements in the vicinity of TA = 30 K, where the appearance of an anomaly in the electrical resistivity was suggested to be due to a progressive reduction of the Os magnetic moment associated with spin fluctuation. Our measurements suggest the absence of prominent change in the spin fluctuations frequency at TA, within the muon probing time scale and the absence of a reduction of the localized Os magnetic moment reflected by the stability within few permille of the local magnetic field strength sensed by the muons below 50 K.

We investigate the physical properties of the Shastry-Sutherland lattice material BaNd$_2$ZnO$_5$. Neutron diffraction, magnetic susceptibility, and specific heat measurements reveal antiferromagnetic order below 1.65 K. The magnetic order is found to be a 2-$\boldsymbol{Q}$ magnetic structure with the magnetic moments lying in the Shastry-Sutherland lattice planes comprising the tetragonal crystal structure of BaNd$_2$ZnO$_5$. The ordered moment for this structure is 1.9(1) $\mu_B$ per Nd ion. Inelastic neutron scattering measurements reveal that the crystal field ground state doublet is well separated from the first excited state at 8 meV. The crystal field Hamiltonian is determined through simultaneous refinement of models with both the LS coupling and intermediate coupling approximations to the inelastic neutron scattering and magnetic susceptibility data. The ground state doublet indicates that the magnetic moments lie primarily in the basal plane with magnitude consistent with the size of the determined ordered moment., Comment: 13 pages, 8 figures

Powder neutron-diffraction experiments have been employed to establish the effects of site-selective magnetic dilution in the ${\mathrm{Sm}}_{2}{\mathrm{MnMnMn}}_{4\ensuremath{-}x}{\mathrm{Ti}}_{x}{\mathrm{O}}_{12} A$-site columnar ordered quadruple perovskite manganites ($x=1, x=2$, and $x=3$). We show that in all three compositions the Mn ions adopt a collinear ferrimagnetic structure below 27, 62, and 34 K, respectively. An unexpected increase in the ordering temperature was observed between the $x=1$ and $x=2$ samples, which indicates a considerable departure from mean-field behavior. This result is corroborated by large reductions in the theoretical ground-state magnetic moments observed across the series, which indicate the presence of spin fluctuations and/or disorder. We show that long-range magnetic order in the $x=3$ sample, which occurs below the percolation threshold for B-B exchange, can only be understood to arise if it is mediated via both A-B and B-B exchange, hence confirming the importance of A-B exchange interactions in these materials. Finally, we show that site-selective magnetic dilution enables the tuning of a ferrimagnetic compensation point and the introduction of temperature-induced magnetization reversal.

A new ternary chromium disulfide, Ba9Cr4S19, has been grown out of BaCWl(2) molten salt. Single-crystal structure analysis revealed that it crystallizes in the centrosymmetric space group C2/c with lattice parameters: a = 12.795(3) angstrom, b = 11.3269(2) angstrom, c = 23.2057(6) angstrom, beta = 104.041(3)degrees, and Z = 4. Ba9Cr4S19 comprises four face-sharing Cr-centered octahedra with disulfide ions occupying sites on each terminal face. The resulting Cr4S15 tetramer units are isolated by nonmagnetic Ba-centered polyhedra in the ab plane and barium disulfide (=Ba-4(S-2)(2)) layers along the c-axis. Following the structure analysis, the title compound should be expressed as [Ba2+](9)[Cr3+](4)[(S-2)(2-)](4)[S2-](11), which is also consistent with Cr2p X-ray photoemission spectra showing trivalent states of the Cr atoms. The unique Cr-based zero-dimensional structure with the formation of these disulfide ions can be achieved for the first time in ternary chromium sulfides, which adopt 1-3 dimensional frameworks of Cr-centered polyhedra.

${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$ is a newly synthesized polar metal in which inversion symmetry is broken by the magnetic frustration in an antiferromagnetic ordering of Co and Os sublattices. The coupled magnetic and structural transition occurs at 45 K at ambient pressure. Here, we perform transport measurements and first-principles calculations to study the pressure effects on the magnetic/structural coupled transition of ${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$. Experimentally, we monitor the resistivity anomaly at ${T}_{N}$ under various pressures up to 11 GPa in a cubic anvil cell apparatus. We find that ${T}_{N}$ determined from the resistivity anomaly first increases quickly with pressure in a large slope of $d{T}_{N}/dP=+6.8(8)\phantom{\rule{0.28em}{0ex}}\mathrm{K}/\mathrm{GPa}$ for $Pl4\phantom{\rule{0.28em}{0ex}}\mathrm{GPa}$ and, then, increases with a much reduced slope of 1.8(4) K/GPa above 4 GPa. Our first-principles calculations suggest that the observed discontinuity of $d{T}_{N}/dP$ around 4 GPa may be attributed to the vanishing of the Os magnetic moment under pressure. Pressure substantially reduces the Os moment and completely suppresses it above a critical value, which relieves the magnetic frustration in the antiferromagnetic ordering of ${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$. The Co and Os polar distortions decrease with the increasing pressure and simultaneously vanish at the critical pressure. Therefore, above the critical pressure, a new centrosymmetric antiferromagnetic state emerges in ${\mathrm{Pb}}_{2}\mathrm{Co}\mathrm{Os}{\mathrm{O}}_{6}$, distinct from the one under ambient pressure, thus, showing a discontinuity in $d{T}_{N}/dP$.

We show that a polar, pseudo-Jahn-Teller instability exists for the underbonded rare-earth $A$-site cations in the quadruple perovskite ${\mathrm{Dy}}_{1\ensuremath{-}\ensuremath{\delta}}{\mathrm{Mn}}_{7+\ensuremath{\delta}}{\mathrm{O}}_{12}$, which leads to the spontaneous formation of a dipolar glass. This observation alone expands the applicability of pseudo-Jahn-Teller physics in perovskite-derived materials, for which it is typically confined to $B$-site cations. We demonstrate that the dipolar glass order parameter is coupled to a ferrimagnetic order parameter via strain, leading to a first order magnetostructural phase transition that can be tuned by magnetic field. This phenomenology may emerge in a broad range of perovskite-derived materials in which $A$-site cation ordering and octahedral tilting are mutually tied to meet the criteria of structural stability.

Polycrystalline samples of $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ were synthesized at ambient pressure (AP) and high pressure (HP) conditions, respectively. Both samples are electrically semiconducting. The AP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ crystallizes in the $6H$ perovskite structure with space group $P{6}_{3}/mmc$, consisting of face-sharing $\mathrm{O}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ dimer units and corner-sharing $\mathrm{Ni}{\mathrm{O}}_{6}$ octahedra. Magnetic measurements indicated that AP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ is antiferromagnetically ordered below 130 K. HP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ crystallizes in the $6H$ perovskite structure too, but the face-sharing octahedral sites appear to be occupied by both $\mathrm{N}{\mathrm{i}}^{2+}$ and $\mathrm{O}{\mathrm{s}}^{5+}$ ions, whereas the corner-sharing site is occupied exclusively by $\mathrm{O}{\mathrm{s}}^{5+}$. HP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ undergoes a high-temperature ($\ensuremath{\approx}\phantom{\rule{0.16em}{0ex}}400\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) weak ferromagnetic transition, which is much different from the antiferromagnetism of the AP phase. The long-range magnetic order of HP $\mathrm{B}{\mathrm{a}}_{3}\mathrm{NiO}{\mathrm{s}}_{2}{\mathrm{O}}_{9}$ was confirmed by neutron powder diffraction. X-ray magnetic circular dichroism analysis supported ferromagnetic coupling between Os and Ni moments which leads to a spin arrangement, where the ferromagnetic moments mainly arise from $\mathrm{N}{\mathrm{i}}^{2+}$ ions.

A new germanate garnet compound, Ce2CaMg2Ge3O12, was synthesized via flux crystal growth. Truncated spherical, reddish-orange single crystals with a typical size of 0.1-0.3 mm were grown out of a BaCl2-CaCl2 melt. The single crystals were characterized by single-crystal X-ray diffraction analysis, which revealed that it adopted a cubic garnet-type structure with a = 12.5487(3) angstrom in the space group Ia-3d. Its composition is best described as A(3)B(2)C(3)O(12), where Ce/Ca, Mg, and Ge occupied the A, B, and C sites, respectively. A UV-vis absorption spectroscopy measurement on the germanate garnet revealed a clear absorption edge corresponding to a band gap of 2.21 eV (lambda = 561 nm). First-principle calculations indicated that the valence band maximum was composed of Ce 4f bands, whereas the conduction band minimum mainly consisted of Ce 5d bands. These findings explain the observed absorption edge through the Ce 4f -> 5d absorption. Photoluminescence emission spectra exhibited a very broad peak centered at 600 nm, corresponding to transition from the lowest energy d level to the 4f levels.

Metallic LiOsO$_3$ undergoes a continuous ferroelectric-like structural phase transition below $T_c$ = 140 K to realize a polar metal. To understand the microscopic interactions that drive this transition, we study its critical behavior above $T_c$ via electromechanical coupling - distortions of the lattice induced by short-range dipole-dipole correlations arising from Li off-center displacements. By mapping the full angular distribution of second harmonic electric-quadrupole radiation from LiOsO$_3$ and performing a simplified hyper-polarizable bond model analysis, we uncover subtle symmetry-preserving lattice distortions over a broad temperature range extending from $T_c$ up to around 230 K, characterized by non-uniform changes in the short and long Li-O bond lengths. Such an extended region of critical fluctuations may explain anomalous features reported in specific heat and Raman scattering data, and suggests the presence of competing interactions that are not accounted for in existing theoretical treatments. More broadly, our results showcase how electromechanical effects serve as a probe of critical behavior near inversion symmetry breaking transitions in metals., Comment: 6 pages main text, 4 figures, 10 pages supplementary information

The perovskite NaOsO3 has a metal–insulator transition at temperature 410 K, which is delicate, intriguing, and provokes a lot of debate on its nature. Our combined electrical resistance, Raman, and synchrotron x-ray diffraction experiments show that the insulating ground state in this osmate endures under high pressure up to at least 35 GPa. In this pressure range, compression reveals hidden hysteretic resistance properties with a transient metallic state near 200 K, manifested three electronic character anomalies (at 1.7, 9.0, and 25.5 GPa), and a structural transition to the singular polar phase (at ~18 GPa). We distinguish NaOsO3 from the regular crystallographic behavior of perovskites, though the electrical specificities resemble iridates and nickelates. The theoretical first-principle band structure and lattice dynamics calculations demonstrate that the magnetically itinerant Lifshitz-type mechanism with spin–orbit and spin–phonon interactions is responsible for these pressure-induced changes. Our findings provide another new playground for the emergence of new states in 5d materials by using high-pressure methods.

We report on the structural, magnetic, and electronic properties of two new double-perovskites synthesized under high pressure; Pb2CaOsO6 and Pb2ZnOsO6. Upon cooling below 80 K, Pb2CaOsO6 simultaneously undergoes a metal--insulator transition and develops antiferromagnetic order. Pb2ZnOsO6, on the other hand, remains a paramagnetic metal down to 2 K. The key difference between the two compounds lies in their crystal structure. The Os atoms in Pb2ZnOsO6 are arranged on an approximately face-centred cubic lattice with strong antiferromagnetic nearest-neighbor exchange couplings. The geometrical frustration inherent to this lattice prevents magnetic order from forming down to the lowest temperatures. In contrast, the unit cell of Pb2CaOsO6 is heavily distorted up to at least 500 K, including antiferroelectric-like displacements of the Pb and O atoms despite metallic conductivity above 80 K. This distortion relieves the magnetic frustration, facilitating magnetic order which in turn drives the metal--insulator transition. Our results suggest that the phase transition in Pb2CaOsO6 is spin-driven, and could be a rare example of a Slater transition., Comment: 14 pages, 9 figures. Accepted as a regular article in Phys. Rev. B

Room-temperature ferrimagnetism was discovered for the anti-site-disordered perovskite $\mathrm{C}{\mathrm{a}}_{2}\mathrm{MnOs}{\mathrm{O}}_{6}$ with ${T}_{\mathrm{c}}=305\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. $\mathrm{C}{\mathrm{a}}_{2}\mathrm{MnOs}{\mathrm{O}}_{6}$ crystallizes into an orthorhombic structure with a space group of Pnma, in which Mn and Os share the oxygen-coordinated-octahedral site at an equal ratio without a noticeable ordered arrangement. The material is electrically semiconducting with variable-range-hopping behavior. X-ray absorption spectroscopy confirmed the trivalent state of the Mn and the pentavalent state of the Os. X-ray magnetic circular dichroism spectroscopy reveals that the Mn and Os magnetic moments are aligned antiferromagnetically, thereby classifying the material as a ferrimagnet which is in accordance with band structure calculations. It is intriguing that the magnetic signal of the Os is very weak, and that the observed total magnetic moment is primarily due to the Mn. The ${T}_{\mathrm{c}}=305\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is the second highest in the material category of so-called disordered ferromagnets such as $\mathrm{CaR}{\mathrm{u}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}{\mathrm{O}}_{3}$, $\mathrm{SrR}{\mathrm{u}}_{1\ensuremath{-}x}\mathrm{C}{\mathrm{r}}_{x}{\mathrm{O}}_{3}$, and $\mathrm{CaI}{\mathrm{r}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x}{\mathrm{O}}_{3}$, and hence, may support the development of spintronic oxides with relaxed requirements concerning the anti-site disorder of the magnetic ions.

We report NMR experiments on heavily electron-doped Fe-based superconductor in comparison with the results on the parent Fe-based compounds. The typical parent Fe-based compound LaFe(As1-x′P x′)O exhibits the re-emergent antiferromagnetic (AFM) order at x′ ~ 0.6 (AFM2) separated from the parent AFM order at x′ =0 (AFM1). Systematic 31P-NMR study on [Sr4Sc2O6]Fe2(As1−x P x )2 (SrSc42622), which has local lattice parameters of iron-pnictogen (FePn) layer similar to the series of LaFe(As1−x′/P x′)O, also revealed that the presence of AFM1 order is universal for most of parent Fe-based compounds. In contrast, the static AFM2 order was absent in this series, however, the dynamical low-energy AFM spin fluctuations are enhanced at around x ~ 0.8, indicating that the onset of the static AFM2 is quite sensitive to the local lattice parameters of FePn layer. In order to elucidate the further universality and diversity, we have carried out 77Se-NMR measurement on Li x (NH3)yFe2−δ Se2 (Tc = 44 K) in heavily electron-doped regime. Although the spin fluctuations at low energies does not significantly develops upon cooling, the moderate spin fluctuations were extracted at high temperatures from comparison of the temperature (T) dependences of Knight shift and nuclear relaxation rate (1/T 1 T). We discuss the universality and diversity of the relationship between the Tc and the characteristics of the spin fluctuations in the Fe-based compounds from a microscopic point of the NMR measurements.

We report a systematic NMR study on [Sr4Sc2O6]Fe-2(As1-xPx)(2), for which the local lattice parameters of the iron-pnictogen (FePn) layer are similar to those of the series LaFe(As1-x'Px')O, which exhibits two segregated antiferromagnetic (AFM) order phases, AFM1 at x' = 0 - 0.2 and AFM2 at x' = 0.4 - 0.7. Our results reveal that the parent AFM1 phase at x = 0 disappears at x = 0.3 - 0.4, corresponding to a pnictogen height (h(pn)) from the Fe plane of 1.3-1.32 angstrom, which is similar to that of LaFe(As1-x'Px')O and various parent Fe pnictides. By contrast, the AFM2 order reported for LaFe(As0.4P0.6)O does not appear at x similar to 0.8, although the local lattice parameters of the FePn layer and the microscopic electronic states are quite similar. Despite the absence of the static AFM2 order, reemergent dynamical AFM spin fluctuations were observed at approximately x similar to 0.8, which can be attributed to the instability of the AFM2 phase. We suggest this re-enhancement of AFM spin fluctuations plays a significant role in enhancing the T-c to 17 K for x = 0.8 - 1. Finally, we discuss the universality and diversity of the complicated magnetic ground states from a microscopic point of view, including the difference in the origins of the AFM1 and AFM2 phases, and their relations with the high superconducting transitions in Fe pnictides.

We report on our investigation on the magnetism of the iridate double perovskite ${\mathrm{Sr}}_{2}{\mathrm{CoIrO}}_{6}$, a nominally ${\mathrm{Ir}}^{5+}$ Van Vleck ${J}_{\mathrm{eff}}=0$ system. Using x-ray absorption (XAS) and x-ray magnetic circular dichroism (XMCD) spectroscopy at the Ir-${L}_{2,3}$ edges, we found a nearly zero orbital contribution to the magnetic moment and thus an apparent breakdown of the ${J}_{\mathrm{eff}}=0$ ground state. By carrying out also XAS and XMCD experiments at the Co-${L}_{2,3}$ edges and by performing detailed full atomic multiplet calculations to simulate all spectra, we discovered that the compound consists of about 90% ${\mathrm{Ir}}^{5+}$ (${J}_{\mathrm{eff}}=0$) and ${\mathrm{Co}}^{3+}$ ($S=2$) and 10% ${\mathrm{Ir}}^{6+}$ ($S=3/2$) and ${\mathrm{Co}}^{2+}$ ($S=3/2$). The magnetic signal of this minority ${\mathrm{Ir}}^{6+}$ component is almost equally as strong as that of the main ${\mathrm{Ir}}^{5+}$ component. We infer that there is a competition between the ${\mathrm{Ir}}^{5+}\ensuremath{-}{\mathrm{Co}}^{3+}$ and the ${\mathrm{Ir}}^{6+}\ensuremath{-}{\mathrm{Co}}^{2+}$ configurations in this stoichiometric compound.

We present the magnetic structure of ${\mathrm{TmMn}}_{3}{\mathrm{O}}_{6}$, solved via neutron powder diffraction. We demonstrate that long-range magnetic order develops below 74 K, and at 28 K a spin-flop transition occurs driven by $f\ensuremath{-}d$ exchange and rare-earth single-ion anisotropy. In both magnetic phases, the magnetic structure may be described as a collinear ferrimagnet, contrary to conventional theories of magnetic order in the manganite perovskites. Instead, we show that these magnetic structures can be understood to arise due to ferro-orbital order, the $A, {A}^{\ensuremath{'}}$, and ${A}^{\ensuremath{'}\ensuremath{'}}$ site point symmetry, $mm2$, and the dominance of $A\ensuremath{-}B$ exchange over both $A\ensuremath{-}A$ and $B\ensuremath{-}B$ exchange, which together are unique to the $R{\mathrm{Mn}}_{3}{\mathrm{O}}_{6}$ perovskites.

A high-pressure synthesis method was employed to prepare Mn-self-doped perovskites (R 0.667Mn0.333)MnO3 (R = Yb, Lu) at about 6 GPa and 1670 K. Crystal and magnetic structures of (Yb0.667Mn0.333)MnO3 have been studied by combining neutron powder diffraction, magnetic susceptibility and specific heat measurements. Within the orthorhombic space group Pnma, magnetic cations are located on site 4c (A site, occupied by two thirds of Yb3+ and one third of Mn2+) and on site 4b (B site, occupied by two thirds of Mn3+ and one third of Mn4+). The degree of structural distortion of the MnO6 octahedra follows the general trend of (R1−x Mn x )MnO3 compounds which shows a decrease with increasing amount of Jahn–Teller inactive Mn4+ cations. Mn–Mn interactions produce a collinear ferrimagnetic structure (T C,Mn = 106 K) with ferromagnetically ordered Mn moments at the B site being coupled antiferromagnetically with ordered Mn moments at the A site. Mn–Yb interactions induce a small but non-zero ferromagnetic Yb3+ moment which can explain a small decrease of the magnetic susceptibility at low temperature. Yb–Yb interactions create an antiferromagnetic structure at T N,Yb ≈ 40 K. Ordered moments of the ferrimagnetic and antiferromagnetic structures are oriented perpendicular to each other within the ac-plane and Yb3+ moments contribute to both structures. The appearance of ordered Yb3+ moments induced by Mn–Yb interactions in perovskite (Yb0.667Mn0.333)MnO3 is a result of the Mn self-doping on the A site and has not been observed in the orthorhombic perovskite modification (space group Pnma) of the undoped parent compound YbMnO3, but interestingly, it also appears in the hexagonal non-perovskite modification (space group P63 cm) of YbMnO3.

A high-pressure synthesis method was employed to prepare (Ho1-xMnx)MnO3 solid solutions with x = 0.2 and 0.3 (at about 6 GPa and 1,670 K) and magnetic properties and structures were investigated by magnetic, dielectric and neutron diffraction measurements. Both samples crystallize in the GdFeO3-type Pnma perovskite structure, and both samples show magnetization reversal behavior below the compensation temperature of about 35 K (at H = 100 Oe). The magnetization reversal phenomena are originated from a ferrimagnetic (FiM) structure which takes place below TC = 76 K (x = 0.2) and 102 K (x = 0.3) and is built from ferromagnetic (FM) ordering of Mn3+ and Mn4+ cations at the B site which are antiferromagnetically (AFM) coupled with Ho3+ and Mn2+ cations at the A site. The magnetic moment of Ho3+ cations increases significantly with deceasing temperature, and it overcomes the saturated magnetic moment of Mn3+ and Mn4+ cations at the B site. Field-induced first-order transitions were found in both compounds below about 35 K. Neutron diffraction measurements on the x = 0.2 sample found a collinear FiM structure between 76 K and 40 K, and the development of spin canting at the A site below 40 K. The coexistence of Ho3+ and Mn2+ at the A-site gives rise to additional short-range magnetic ordering of Ho3+ and to strain effects along the a-direction which are stronger than in (R1−xMnx)MnO3 materials with heavier and smaller rare-earths cations.

The structure of a polycrystalline sample of SrOsO 3 has been investigated using powder neutron diffraction from 5 to 300 K, and powder synchrotron X-ray diffraction from 80 to 870 K. At low temperatures SrOsO 3 is orthorhombic in Pbnm and heating results in a sequence of phase transition transitions Pbnm → Imma → I 4 / mcm → Pm 3 m . This behavior is compared to that of other Sr containing perovskites. Comparison of the transition temperatures in Sr B O 3 perovskites shows that the tolerance factor alone does not determine the temperature at which the cubic phase is stabilized but rather the electronic configuration of the B-site cation appears to be significant.