Antiferromagnetic-like Transition Research Articles

Mn2Ga2S5 and Mn2Al2Se5 van der Waals Chalcogenides: A Source of Atomically Thin Nanomaterials.

Layered chalcogenides containing 3d transition metals are promising for the development of two-dimensional nanomaterials with interesting magnetic properties. Both mechanical and solution-based exfoliation of atomically thin layers is possible due to the low-energy van der Waals bonds. In this paper, we present the synthesis and crystal structures of the Mn2Ga2S5 and Mn2Al2Se5 layered chalcogenides. For Mn2Ga2S5, we report magnetic properties, as well as the exfoliation of nanofilms and nanoscrolls. The synthesis of both polycrystalline phases and single crystals is described, and their chemical stability in air is studied. Crystal structures are probed via powder X-ray diffraction and high-resolution transmission electron microscopy. The new compound Mn2Al2Se5 is isomorphous with Mn2Ga2S5 crystallizing in the Mg2Al2Se5 structure type. The crystal structure is built by the ABCBCA sequence of hexagonal close-packing layers of chalcogen atoms, where Mn2+ and Al3+/Ga3+ species preferentially occupy octahedral and tetrahedral voids, respectively. Mn2Ga2S5 exhibits an antiferromagnetic-like transition at 13 K accompanied by the ferromagnetic hysteresis of magnetization. Significant frustration of the magnetic system may yield spin-glass behavior at low temperatures. The exfoliation of Mn2Ga2S5 layers was performed in a non-polar solvent. Nanolayers and nanoscrolls were observed using high-resolution transmission electron microscopy. Fragments of micron-sized crystallites with a thickness of 70-100 nanometers were deposited on a glass surface, as evidenced by atomic force microscopy.

Structural and Magnetic Properties of the B-Site-Ordered Double Perovskites Ln2NiTiO6 (Ln = La, Pr, and Nd)

Abstract Structural and magnetic properties of B-site-ordered double perovskites Ln2NiTiO6 (Ln = La, Pr, and Nd) were investigated. The charge formulas were revealed to be Ln23+Ni2+Ti4+O6, which gave a geometrically frustrated face-centered cubic lattice consisting of magnetic Ni2+ (S = 1) cations. In spite of the geometrical spin frustration of Ni2+ spins, the samples show an antiferromagnetic-like magnetic transition at temperatures TN close to their absolute values of the Weiss temperature θ, giving small frustration indices f = |θ|/TN ∼ 1. The small f values are considered to be due to some amount of anti-site disorder between Ni2+ and Ti4+ originating in the small valence difference. The suppression of magnetic ordering in the geometrically frustrated system is strongly affected by the B-site cation ordering in the double perovskites.

Mn(Pt1−xPdx)5P : Isovalent tuning of Mn-sublattice magnetic order

We report the growth and characterization of ${\mathrm{MnPd}}_{5}\mathrm{P}$, a rare-earth-free ferromagnet, with ${T}_{C}\ensuremath{\approx}295\phantom{\rule{4pt}{0ex}}\mathrm{K}$ and planar anisotropy, and conduct a substitutional study with its antiferromagnetic analog ${\mathrm{MnPt}}_{5}\mathrm{P}$. All compounds in the family adopt the layered anti-${\mathrm{CeCoIn}}_{5}$-type structure with the space group $P4/mmm$, and EDS and x-ray diffraction results indicate that ${\mathrm{MnPt}}_{5}\mathrm{P}$ and ${\mathrm{MnPd}}_{5}\mathrm{P}$ form a complete solid solution. Based on measurements of the temperature- and field-dependent magnetization and resistance, we construct a temperature-composition ($T\text{\ensuremath{-}}x$) phase diagram for $\mathrm{Mn}{({\mathrm{Pt}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x})}_{5}\mathrm{P}$ and demonstrate that the essentially antiferromagnetic order found in ${\mathrm{MnPt}}_{5}\mathrm{P}$ is extraordinarily sensitive to Pd substitution. At low Pd fractions ($x<0.010$), the single antiferromagnetic-like transition in pure ${\mathrm{MnPt}}_{5}\mathrm{P}$ splits into a higher-temperature ferromagnetic transition followed first, upon cooling, by a lower temperature ferromagnetic to antiferromagnetic transition and then by a re-entrant antiferromagnetic to ferromagnetic transition at even lower temperatures. The antiferromagnetic region makes up a bubble phase that persists up to $x\ensuremath{\approx}0.008$--0.009 for $T\ensuremath{\approx}150\phantom{\rule{4pt}{0ex}}\mathrm{K}$, with all samples $0\ensuremath{\le}x<0.008$ recovering their initial ferromagnetic state upon further cooling to base temperature. Once $x>0.010$, $\mathrm{Mn}{({\mathrm{Pt}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x})}_{5}\mathrm{P}$ undergoes a only single transition into the ferromagnetic phase. The Curie temperature initially increases rapidly with $x$, rising from ${T}_{C}\ensuremath{\approx}197\phantom{\rule{4pt}{0ex}}\mathrm{K}$ at $x$ = 0.013 to a maximum of ${T}_{C}\ensuremath{\approx}312\phantom{\rule{4pt}{0ex}}\mathrm{K}$ for $x\ensuremath{\approx}0.62$, and then falling back to ${T}_{C}\ensuremath{\approx}295\phantom{\rule{4pt}{0ex}}\mathrm{K}$ for pure ${\mathrm{MnPd}}_{5}\mathrm{P}$ $(x=1.00)$. Given that Pt and Pd are isoelectronic, this work raises questions as to the origin of the extreme sensitivity of the magnetic ground state and the nature of the re-entrant ferromagnetism at dilute Pd levels.

Spin-Glass-like State and Reversible Room-Temperature Magnetocaloric Effect in Double Distorted Perovskites Nd(Cu3-xMnx)Mn4O12.

The preparation, complex magnetic properties and room-temperature magnetocaloric effect in Nd(Cu3-xMnx)Mn4O12 with cation distribution (Nd3+)A(Cu3-x2+xMnx3+)A'(Mn1+x3+Mn3-x4+)BO122- (x = 1 and 1.5) have been reported. Both compounds show a sharp paramagnetic-ferromagnetic (FM) transition at TC of 300 and 280 K, respectively. The substitution of Cu by Mn at the A' site induces the emergence of a spin glass state below ≈63 K for x = 1 and ≈72 K for x = 1.5 compound. Another antiferromagnetic-like magnetic transition is also observed in both compounds at 23 and 28 K, respectively, which is discussed as the antiferromagnetic coupling between Nd3+ at the A' site and (Mn3+/Mn4+) at the B site. These two compounds exhibit room-temperature magnetocaloric effect. For a small field of 2 T, the maximum magnetic entropy changes -ΔSM are 1.5 J/kg K at 300 K and 1.4 J/kg K at 280 K, respectively. Moreover, the -ΔSM(T) curves show an asymmetric distribution, resulting in high refrigerant capacity values for both compounds. We further demonstrate the distinct roles of the A'- and B-site spins on the magnetic properties and the origin of the spin-glass-like state in double distorted perovskites Ln(Cu3-xMnx)Mn4O12 family of compounds.

A New Superconductor Parent Compound NaMn6Bi5 with Quasi-One-Dimensional Structure and Lower Antiferromagnetic-Like Transition Temperatures

Mn-based superconductors are very rare and their superconductivity has only been reported in three-dimensional MnP and quasi-one-dimensional KMn6Bi5 and RbMn6Bi5 with [Mn6Bi5]− columns under high pressures. Here we report the synthesis, magnetism, electrical resistivity, and specific heat capacity of the newly discovered quasi-one-dimensional NaMn6Bi5. Compared with other AMn6Bi5 (A = K, Rb, and Cs), NaMn6Bi5 has abnormal Bi-Bi bond lengths and two antiferromagnetic-like transitions at 47.3 K and 51.8 K. Anisotropic resistivity and low-temperature non-Fermi liquid behavior are observed. Heat capacity measurement reveals that the Sommerfeld coefficient for NaMn6Bi5 is unusually large. Using first-principles calculations, an unusual enhancement of density of states near the Fermi level is demonstrated for NaMn6Bi5. The features make NaMn6Bi5 a more suitable platform to explore the interplay of magnetism and superconductivity.

Field-driven spin reorientation in SmMnO3 polycrystalline powders

The SmMnO3 perovskite system shows interesting magnetic properties and making them an attractive material for specific technological application. However, these materials on nanosized dimension display properties that can be significantly different from their bulk dimension. In this regard, using the sol-gel method, the successful synthesis of SmMnO3 polycrystalline powders is herein reported. The structure, morphology, vibrational and magnetic properties of the as-produced sample have been investigated. X-ray diffraction pattern shows a single-perovskite SmMnO3 crystalline phase structure, with a crystalline size of ∼70 nm. The room temperature Raman spectrum confirms the formation of the perovskite SmMnO3 crystalline structure observed by XRD. DC magnetic measurements show an antiferromagnetic-like transition at 60 K (TN ≈ 60 K), attributed to the antiferromagnetic ordering of the Mn3+ spins, magnetic measurements also reveal a temperature-induced magnetization reversal phenomenon characterized by the magnetic compensation temperature (Tcomp ≈ 6 K), attributed to antiparallel orientation of weak ferromagnetic Mn3+- and Sm3+-ion magnetic moments induced by Sm3+-Mn3+ exchange interaction. Magnetization loops, recorded from the as-synthesized SmMnO3 sample contain some singularity compared to previous studies of SmMnO3, which are assigned to small particle size and single domain character of the particles, which are characterized by two well-defined anomalies, both connected with the spin inversion phenomena: one at low fields showing increasing and decreasing branches intersecting each other; another at high fields revealing sudden jumps. The study of a Schottky anomaly in the specific heat measurements recorded at low temperatures (below 10 K) under DC magnetic fields (in the range 5–14 T), is consistent with the presence of a field-driven spin reorientation, from antiferromagnetic to a net ferromagnetic order.

Magnetic and magneto-transport studies of two-dimensional ferromagnetic compound Fe3GeTe2

We have systematically reported the magnetic and magneto-transport properties of two-dimensional itinerant ferromagnetic compound Fe3GeTe2 at high magnetic fields of 58 T and demonstrated the correlation between its transport and magnetism. Anomalous two-steps magnetic ordering and antiferromagnetic-like transitions in zero field-cooling (ZFC) curves for H ∥ ab-plane are observed. Additionally, we find that intrinsic negative magnetoresistances in bulk Fe3GeTe2 single crystal are mainly attributed to the suppression of spin-fluctuations in low magnetic fields. Complex evolutions of temperature dependent high field magnetoresistances are detected under different magnetic field and current configurations, which can be explained as a result of the competition between spin-fluctuations, the magnon-scatterings and classical cyclotronic effects.

Neutron scattering study of commensurate magnetic ordering in single crystal CeSb2

Temperature and field-dependent magnetization M(T, H ) measurements and neutron scattering study of a single crystal CeSb2 are presented. Several anomalies in magnetization curves have been confirmed, i.e., at 15.6 K, 12 K, and 9.8 K, respectively. These three transitions are all metamagnetic transitions, which shift to lower temperatures as the magnetic field increases. In contrast to the previous studies that the anomaly at 15.6 K has been suggested as paramagnetic to ferromagnetic phase transition, in our measurement no hysteresis loop around zero field with either H ∥ c or H ⊥ c has been observed. The anomaly located at around 12 K is antiferromagnetic-like transition, and this turning point will clearly split into two when the magnetic field H ⩾ 2 kOe. A neutron scattering study reveals that the low temperature ground state of CeSb2 orders magnetically with commensurate propagation wave vectors k = (−1, ±1/6, 0) and k = (±1/6, −1, 0), with phase transition temperature TC ∼ 9.8 K.

Crystal Growth and the Magnetic Properties of Na2Co2TeO6 with Quasi-Two-Dimensional Honeycomb Lattice

Single crystal Na2Co2TeO6 has been successfully grown by self-flux method, and its lattice structure and basic magnetic properties were characterized. As determined by single crystal X-ray diffraction, Na2Co2TeO6 belongs to space group P6322 (182) with a = b = 5.2709(2) A, c = 11.2615(15) A, and V = 270.95 (4) A3, the crystal structure is a layered honeycomb formed by CoO6 octahedra and the TeO6 octahedra in the center of the honeycomb layers, and the NaO6 octahedra are between the honeycomb layers. Magnetic susceptibility measurements indicate that the single crystal sample displays a distinct anisotropic behavior and the spin parallels the honeycomb plane (ab-plane). In a lower temperature region, a series of antiferromagnetic-like (AFM-like) phase transitions were observed, which may result from the spin reorientation of Co2+ ions. The different magnetization behavior between the polycrystalline structure and the single crystal (with the magnetic field parallel to and perpendicular to the ab-plane) rev...

Magnetic structures of rare earth intermetallic compounds RCuAs2 (R = Pr, Nd, Tb, Dy, Ho, and Yb)

Neutron scattering studies have been carried out on polycrystalline samples of a series of rare earth intermetallic compounds RCuAs2 (R = Pr, Nd, Dy, Tb, Ho and Yb) as a function of temperature to determine the magnetic structures and the order parameters. These compounds crystallize in the ZrCuSi2 type structure, which is similar to that of the RFeAsO (space group P4/nmm) class of iron-based superconductors. PrCuAs2 develops commensurate magnetic order with K = (0, 0, 0.5) below TN = 6.4(2) K, with the ordered moments pointing along the c-axis. The irreducible representation analysis shows either a Γ12 or Γ13 representation. NdCuAs2 and DyCuAs2 order below TN = 3.54(5) K and TN = 10.1(2) K, respectively, with the same ordering wave vector but the moments lying in the a-b plane (with a Γ29 or Γ210 representation). TbCuAs2 and HoCuAs2 exhibit incommensurate magnetic structures below TN = 9.44(7) and 4.41(2) K, respectively. For TbCuAs2, two separate magnetic ordering wave vectors are established as K1(Tb) = (0.240,0.155,0.48) and K2(Tb) = (0.205, 0.115, 0.28), whereas HoCuAs2 forms a single K(Ho) = (0.121, 0.041, 0.376) magnetic structure with 3rd order harmonic magnetic peaks. YbCuAs2 does not exhibit any magnetic Bragg peaks at 1.5 K, while susceptibility measurements indicate an antiferromagnetic-like transition at 4 K, suggesting that either the ordering is not long range in nature or the ordered moment is below the sensitivity limit of ≈0.2 μB.

Nontrivial Recurrent Intergrowth Structure and Unusual Magnetic Behavior of Intermetallic Compound Fe32+δGe33As2.

A new phase Fe32+δGe33As2 (δ ≤ 0.136) was obtained by two-step synthesis from the elements. Fe32+δGe33As2 crystallizes in its own structure type (space group P6/mmm, Z = 1, a = 11.919(3) Å, c = 7.558(4) Å) that can be described as a recurrent two-dimensional intergrowth of two intermetallic structure types, MgFe6Ge6 and Co2Al5. Their blocks are represented by infinite columns in the structure. No visible structural changes were observed in the temperature range from 10 to 300 K. At 125 K, Fe32+δGe33As2 undergoes an antiferromagnetic-like transition, while above 150 K it shows a typical Curie-Weiss paramagnetic behavior. Below the transition temperature, a peculiar field-dependent magnetic susceptibility, that shows a significant increase of the susceptibility upon increasing the magnetic field, and a change in transport properties have been observed. Above 140 K, Fe32+δGe33As2 reveals a metallic behavior, in agreement with electronic structure calculation, while below this point the resistivity nonmonotonically increases upon cooling. The Seebeck coefficient is positive, indicating that holes are the major charge carriers, and shows a broad maximum around 57 K.

Magnetic order of Y3NiSi3-type R3NiSi3 (R=Gd–DY) compounds

Magnetic measurements and neutron powder diffraction investigations on the Y3NiSi3-type R3NiSi3 compounds (R=Gd, Tb, Dy) reveal their complex antiferromagnetic ordering. Magnetic measurements on Gd3NiSi3, Tb3NiSi3 and Dy3NiSi3 indicate antiferromagnetic-like transition at temperatures 260K, 202K and 140K, respectively. Also, the Tb3NiSi3 and Dy3NiSi3 compounds show spin-reorientation transition at 132K and 99K, respectively. Below the spin-reorientation transition, the isothermal magnetization curves indicate the metamagnetic-like behavior of Tb3NiSi3 and Dy3NiSi3. The magnetocaloric effect of Dy3NiSi3 is calculated in terms of isothermal magnetic entropy change and it reaches a maximum value of −1.2J/kgK and −1.1J/kgK for a field change of 50kOe near 146K and 92K, respectively. The neutron diffraction studies of Tb3NiSi3 suggest the magnetic ordering of the Tb2 4j sublattice and no magnetic ordering of the Tb1 2a sublattice. Tb3NiSi3 transforms from the high temperature paramagnetic state to the commensurate high-temperature a- and c-axis antiferromagnet of I′2/m magnetic space group below 250K. Below 150K, the high-temperature antiferromagnet transforms into the low-temperature a-, b- and c-axis antiferromagnet of I′i magnetic space group. At 1.5K, the terbium magnetic moment in Tb2 sublattice and its a-, b- and c-axis components reach the values of MTb2=8.2(1) μB, MaTb2=5.9(1) μB, MbTb2=4.3(2) μB and McTb2=3.7(2) μB, respectively.

Tuning a cation distribution and microstructure of CoMn2O4nanoparticles: structural and magnetic studies

Complex metal oxides, especially one crystallizing in the spinel-type family AB2O4, represent an important class of functional materials. Their unique chemical, electric, magnetic and mechanical properties have found versatile applications ranging from energy storage and conversion to magnetism, electronics and catalysis.13 Majority of recent work on spinels appears to be strongly focused on electrochemical properties, while the structural and magnetic studies have been scarce in spite of few papers reporting on very intriguing and complex but still poorly understood magnetic behaviour.4, 5 In this study we have exploited the possibility of novel synthetic route to tune the structural and microstructural properties by simple alternations in preparation conditions, 6, 7 and to, furthermore, correlate these effects to magnetic behaviour. The samples were prepared by thermal decomposition of a heterometallic single-molecular precursor {; ; [Co(bpy)3] [Mn2(C2O4)3].H2O}; ; n (1) (bpy =2, 2 bypiridine) at T=500, 700, 800 1000 C. The X-ray powder diffraction revealed increase in the unit-cell parameters of CoMn2O4 with the increase of formation temperature. This indicated on thermally induced increase of the inversion parameter within spinel lattice. Pronounced changes in the cation distribution, i.e. substitution of Co2+ by Mn3+ on the tetrahedral A site, and vice versa on the octahedral B site, were confirmed by the increase of octahedral octMO and decrease of tetrahedral tetMO bond distances. Crystal structure and graphical result of the final Rietveld refinement for the CoMn2O4 phase treated at 800 C, is shown in Fig. 1. Increase of the applied decomposition temperature was reflected greatly on the magnetic behavior of CoMn2O4, including the increase of hysteresis width, increase of blocking temperature and raised expression of the low temperature antiferromagnetic-like transition. Those effects could originate from the nano-particle growth and increasedanisotropy due to change of the inversion, as well as from the rearrangement of interactions between the spins.

New orthorhombic derivative of CaCu5-type structure: RNi4Si compounds (R=Y, La, Ce, Sm, Gd–Ho), crystal structure and some magnetic properties

The crystal structure of new YNi4Si-type RNi4Si (R=Y, La, Ce, Sm, Gd–Ho) compounds has been established using powder X-ray diffraction. The YNi4Si structure is a new structure type, which is orthorhombic derivative of CaCu5-type structure (space group Cmmm N 65, oC12).GdNi4Si and DyNi4Si compounds order ferromagnetically at 25 and 19K, respectively whereas YNi4Si shows antiferromagnetic nature. At 15K, DyNi4Si shows second antiferromagnetic-like transition. The magnetic moment of GdNi4Si at 5K in 50kOe field is ~7.2μB/f.u. suggesting a completely ordered ferromagnetic state. The magnetocaloric effect of GdNi4Si is calculated in terms of isothermal magnetic entropy change and it reaches the maximum value of −12.8J/kgK for a field change of 50kOe near TC ~25K.

Effect of the short-range interaction on critical phenomena in elastic interaction systems

The elastic interaction, induced by the lattice distortion due to the difference of the molecular size, causes an effective long-range interaction. In spin-crossover (SC) compounds, local bistable states, i.e., high-spin and low-spin states, have different molecular sizes, and the elastic interaction is important. In bipartite lattices, e.g., the square lattice, the ground state can be two types of phases: ferromagneticlike and antiferromagneticlike phases. In systems like SC compounds, the former phase consists of all small or large molecules, and the latter phase has the configuration of alternating small and large molecules. In fact, both cases are observed in SC systems. In this paper we have studied the effect of the short-range interaction in the elastic system on the properties of those order-disorder phase transitions. We have obtained a phase diagram in the coordinates of the temperature and the strength of the short-range interaction, including the metastable structures. We show that effects of the short-range interaction are essentially different for ferromagneticlike and antiferromagneticlike phase transitions. In the ferromagneticlike transition, the long-range interaction of elasticity is relevant, and the system exhibits a phase transition in the mean-filed universality class. In this case, the long-range interaction strongly enhances the ferromagneticlike order, and it works cooperatively with the short-range interaction. In contrast, in the antiferromagneticlike transition, the elastic interaction slightly enhances the antiferromagneticlike order, but essentially it does not contribute to the ordering, and the system shows a transition in the Ising universality class. We have found that in the border region between ferromagneticlike and antiferromagneticlike phases, the antiferromagneticlike phase has an advantage at finite temperatures. We discuss the critical properties of two-step SC transitions with comparison between the elastic interaction model and conventional SC models (Ising-like models).

Synthesis and properties of a new quadruple perovskite: A-site ordered PbMn3Mn4O12

PbMn3Mn4O12 a quadruple perovskite was prepared by high pressure and high temperature synthesis. Powder X-ray diffraction (PXD) and differential scanning calorimetry reveal a structural phase transition at ∼380K. Rietveld refinement of the synchrotron room temperature data indicate rhombohedral symmetry (R-3) with a=6.43675(4)Å and α=109.556(2)°. Similar 423K PXD data refined in a body centered cubic cell (Im-3) with a=7.4283(9)Å. The temperature variation of magnetization, shows a magnetic field dependent antiferromagnetic-like transition at 68K, and dynamic fluctuations indicative of magnetic frustration. The semiconducting electrical behavior indicates a large decrease in the conductivity near 68K. The temperature dependence of the real part of the dielectric constant, εreal increases dramatically at ∼68K, and shows relaxor-type ferroelectric behavior as a function of frequency. The intimate coupling of magnetic, electrical and dielectric properties at 68K in PbMn3Mn4O12 suggests possible multiferroic behavior.

Structural and Magnetic Properties of YBa2Ru0.85Cu0.15O6 and Sr2Re0.69Ca0.31CuO6 Perovskites

In this present investigation, both YBa2Ru0.85Cu0.15O6 and Sr2Re0.69Ca0.31CuO6 perovskite compounds were prepared through high pressure/high temperature (HPHT) synthetic route. The as-prepared samples were structurally characterized by powder X-ray diffraction technique and their magnetic properties were measured. Both compounds crystallized in cubic symmetry with a different space group. The refined lattice parameter for the YBa2Ru0.85Cu0.15O6 and Sr2Re0.69Ca0.31CuO6 compounds are found to be a=8.332(2) A with space group, Fm-3m (225) and a=7.967(4) A space group Pm-3m (221), respectively. The cuprate ordered perovskite compound shows ferromagnetism with high Curie temperature, Tc at ∼450 K whereas the YBa2Ru0.85Cu0.15O6 compound reveals mixed magnetic natures below ∼170 K which is complicated by the presence of magnetic order in the Ru and Cu sublattices. Below 170 K, the compound shows two antiferromagnetic-like transitions (in ZFC mode) at ∼135 K and ∼60 K. With a further decrease of temperature (below 60 K), the susceptibility crosses negative (diamagnetic) signal at ∼35 K and shows maximum negative susceptibility at ∼11 K. By decreasing the temperature below 11 K, the negative susceptibility decreases and shows positive magnetic susceptibility at 2 K. In the fc mode curve, the sample shows broad antiferromagnetic like transition at ∼55 K. At low temperature (below 30 K), an increase in susceptibility signal is seen in the fc magnetic susceptibility curve. The magnetic parameters, such as Weiss temperature, θw and the effective paramagnetic moment, peff obtained from the linear region of χ−1(T) plots are found to be −307.25 K and 3.74 μB/Ru, respectively, for the YBa2Ru0.85Cu0.15O6 compound. The negative sign of θw reveals the antiferromagnetic correlations of the compound. While these studied compounds are already known to the literature, the synthesis method (HPHT) employed for the present YBa2Ru0.85Cu0.15O6 compound is a new approach and quite different from the routine conventional solid state synthesis approach.

Magnetization reversal and Yb3+/Cr3+ spin ordering at low temperature for perovskite YbCrO3 chromites

The temperature dependence of the dc magnetization and the specific heat capacity are systematically investigated for the perovskite YbCrO3 chromites. The results show that there exist two complex sequences of magnetic transitions with the characteristics of magnetization reversal and Yb3+/Cr3+ spin ordering at different temperature, respectively. The antiferromagneticlike transition around TN=118 K is attributed to the antiferromagnetic ordering of the Cr3+ spins and a negative magnetization, accompanied with a tendency to the plateau below 10 K caused by the Yb3+ ordering. We obtain the Weiss constant of −197.0 K and an effective moment of 5.99μB for the sum of the free ion values of 4.53μB for Yb3+ and 3.87μB for high-spin Cr3+ from the experiments, which shows an antiferromagnetic interaction and the existence of weak canted antiferromagnetic (CAFM) characteristics. Corresponding to the magnetic phase transition in the Cr sublattice, the specific heat capacity under zero fields exhibits a sharp λ-shape peak near temperature TN, which is depressed and broadened smoothly with the increase in the magnetic field. And a shoulder-shaped Schottky-type anomaly below 12 K is observed in the specific heat capacity curves. This can be interpreted by accounting for the molecular field approximation by assuming that the induced polarization of the paramagnetic ytterbium ions is opposite to the ferromagnetic moment of the chromium ions. According to the results of the zero fields cooling and the field cooling magnetization, the possible existence of spin ordering for the Yb3+ moments can be predicted.

ChemInform Abstract: Formation of Cubic URh4In and UPd4.5In0.5 Phases and Their Characterization by X-Ray-Diffraction, Magnetic-Susceptibility, and Electrical-Resistivity Measurements.

Abstract The ternary phases URh4In and UPd4.5In0.5 are formed and their polycrystalline samples are found by X-ray diffraction to adopt the cubic AuCu3-type structure, with room-temperature lattice parameters of 399.5±0.2 and 407.0±0.5 pm, respectively, similar to the structure and lattice parameters in the related binary phases URh3 and UPd5−x, respectively. Measurements of the dc-magnetic susceptibility show in URh4In a weak temperature dependence at high temperatures and a rise at lower temperatures, while in UPd4.5In0.5 a Curie–Weiss behaviour (with θp=−84 K and μeff=3.02 μB) at high temperatures and an antiferromagnetic-like transition at Tmax=18±1 K is observed. The temperature dependence of the electrical resistivity ρ(T) of URh4In indicates a metallic character with a BT2.5 dependence at low temperatures. A similar character of ρ(T) at high temperatures is exhibited also by UPd4.5In0.5. However, the latter exhibits a different low-temperature behaviour, involving a small maximum in the resistivity just below Tmax, the size of this maximum being reduced under applied magnetic field.

Convergent beam electron diffraction study on ge-based oxide spinels

Transition metal oxides with spinel crystal structure exhibit intriguing and non trivial magnetic phenomena owing to magnetic frustration between spins having antiferromagnetic coupling interaction on triangle or kagome lattice. GeCo2O4(GCO) and GeNi2O4(GNO), which belong to above category, are very rare normal spinels containing Ge ion. Both reveal antiferromagnetic-like phase transitions at 20 K and 12 K, respectively. According to previous neutron and x-ray diffraction measurements, GNO keeps its cubic structural symmetry down to 2 K which is not natural because such a magnetic transition tends to associate with symmetry breaking structural transitions. In order to know whether the structural transition or symmetry change occur or not at the magnetic transition in detail, convergent beam electron diffraction measurements is employed for the compounds.