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Nanocrystalline samples of undoped dysprosium oxide (Dy2O3) and Ni2+ doped Dy2O3 (Dy1.90Ni0.10O3-δ/DNO) are prepared by co-precipitation method. X-ray diffraction (XRD) analysis by Maud software confirmed the desired crystallographic phase of both samples and also the substitution of Ni2+ ion in Dy2O3 lattice. Absence of impurity is confirmed from Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and high resolution transmission electron microscope (HRTEM) analysis. Magnetization vs. field (M-H) loop of DNO recorded at 5 and 10 K shows clear hysteresis loop with magnetization ∼138.71 emu/g at 5 K and ∼121.52 emu/g at 10 K with applied magnetic field of 5 T. The deviation of inverse susceptibility vs. temperature curve from Curie-Weiss fitting below ∼30 K and also the deviation of initial magnetization data of M-H loop recorded at 30 K from linear fitting suggests that the DNO is in mixed paramagnetic and ferromagnetic phase at and below ∼30 K. Defect mediated ferromagnetic ordering found in DNO at low temperature, is analyzed by bound magnetic polaron model.

Nanocrystalline ZnO and Yb-doped ZnO (Zn0.98Yb0.02O) are prepared by simple co-precipitation method. The pure crystallographic phases of ZnO and Zn0.98Yb0.02O are confirmed by Rietveld analyses of XRD patterns. Raman and photoluminescence spectra recorded at room temperature (RT) indicates that lattice defects and oxygen vacancy in Zn0.98Yb0.02O is more than that of ZnO. Magnetic measurements of ZnO and Zn0.98Yb0.02O are carried out from 300 to 5 K. Ferromagnetic ordering is observed in Zn0.98Yb0.02O at RT and the strength of the ordering increases with the lowering of temperature. Ferromagnetism of Zn0.98Yb0.02O is attributed to the oxygen vacancy introduced by annealing in vacuum. Magnetization vs. temperature curve is well fitted by the combination of 3D spin wave and Curie-Weiss law, which suggest simultaneous presence of para- and ferro-magnetic phases in Zn0.98Yb0.02O. Ferromagnetic ordering is successfully explained by vacancy mediated bound-magnetic polaron model.

To enhance the magnetoelectric property of GaFeO 3 (GFO), Al 3+ doped samples (Al x Ga (1−x) FeO 3 , x=0.05, 0.10 and 0.20) are prepared by the sol-gel technique. Crystallographic phases of the samples are confirmed by X-ray diffractograms. Morphology, average size of nanoparticles including the distribution of sizes are obtained from the results of field emission scanning electron microscopy and high-resolution transmission electron microscopy. Distribution of blocking temperatures and magnetocrystalline anisotropy are determined from the analyses of the observed magnetic hysteresis loops and thermal variation of magnetization curve under zero field cooled and field cooled conditions. Variations of dielectric constant and dielectric loss with frequency show the dispersion in the low frequency region. Ferroelectric orderings have been improved in the doped samples compared to that of GFO. Polarization vs. electric field loops recorded at room temperature indicate that. Magnetic field dependent dielectric constant and negative magneto-capacitance co-efficient of the samples measured at room temperature confirmed that all the samples are multiferroic. Raman spectra and their analyses provide a greater insight into the phase purity and physical properties of the samples. Simultaneous enhancement in magnetic and electric polarizations together with the presence of magneto-electric coupling in the doped samples may enhance the quality of applications in devices.

The magnetic properties of a melt-spun Cu 60 Au 35 Fe 5 alloy are examined by X-ray diffraction (XRD), magnetic measurements, and transmission electron microscopy (TEM). The XRD pattern of an as-spun sample indicates the formation of a solid solution of Cu and Au with no Fe phase, whereas that of the annealed sample (773 K × 36 ks) shows a small amount of the α-Fe phase because the Fe atoms precipitate during annealing. TEM observations and EDX analysis of the as-spun sample show no distinct Fe-rich domains, implying that some Fe atoms are dissolved in the matrix, and others form very fine magnetic clusters. Moreover, magnetic measurements indicate the presence of magnetic clusters and isolated Fe atoms. The AC magnetic susceptibilities show that the as-spun sample has a sharp cusp around 20 K, which is characteristic of spin glass behavior. The simulations of the M – H curves of the as-spun sample measured at 77 and 300 K, show that most Fe atoms are dissolved in the matrix as isolated atoms, not as clusters. Additionally, the calculated rate of clustering in the as-spun sample tends to decrease with temperature, suggesting that the magnetic exchange interactions are weak.

The magnetic properties of a melt-spun Fe-dilute Cu 60 Ag 35 Fe 5 alloy are examined by X-ray diffraction, magnetic measurements, and transmission electron microscopy (TEM). The X-ray diffraction patterns show that the as-spun and annealed (773 K×36 ks) samples contain Cu and Ag phases and no Fe phases; thus, most Fe atoms are dispersed as clusters. Magnetic measurements indicate that the as-spun and annealed samples exhibit superparamagnetic behavior at 300 K, whereas ferromagnetic and superparamagnetic behaviors coexist at 4.2 K. The magnetic moments of small clusters at 300 K are determined by the nonlinear least squares method as 5148 and 4671 μ B for as-spun and annealed samples, respectively, whereas those at 300 K are experimentally determined as 3500 and 3200 μ B . This decrease in magnetic moments may imply the formation of anti-ferromagnetic coupling by annealing. TEM observation of the melt-spun sample suggests that there are three regions with different compositions: Cu-rich, Ag-rich, and Fe-rich with no precipitation in the matrix. In addition, these regions have obscure interfaces. The magnetic clusters are attributed to the Fe-rich regions.

In order to elucidate the dependence of the magnetic ground state on the Ca content (x) in Sr1-xCaxCo2P2 (0 ≤x ≤1, ThCr2Si2-type structure), we have performed muon spin rotation− and relaxation (μ+SR) experiments on Sr1-xCax Co2P2 powder samples mainly in a zero applied field. The end member compound, SrCo2P2, is found to be paramagnetic down to 19 mK. As x increases, such a paramagnetic ground state is observed down to 1.8K until x = 0.45. Then, as x increases further, a short-range antiferromagnetic (AF) ordered phase appears at low temperatures for 0.48 ≤ x ≤ 0.75, and finally, a long-range AF ordered phase is stabilized for x > 0.75. The internal magnetic field of the other end member compound, CaCo2P2, is well consistent with that of the A-type AF order state, which was proposed from neutron scattering experiments. The phase diagram determined with μ+SR is different from that proposed by macroscopic measurements. For an isostructural compound, LaCo2P2, static magnetic order is found to be formed below

The ThCr2Si2-type layered compound SrCo2P2 shows an itinerant-electron metamagnetic transition at high magnetic field. To investigate substitution effects on the itinerant metamagnetic transition, we synthesized Sr[1-x]LaxCo2P2 and SrCo2(P[1-x]Gex)2 and measured their magnetic properties, including magnetizations under pulsed high magnetic fields. We have revealed a strong x dependence of the metamagnetic transition which is consistent with the band theory describing the physical properties in metals., 20th International Conference on Magnetism, ICM 2015

Nanoparticles of Fe-doped europium oxide (Eu 1.90 Fe 0.10 O 3− δ ) are prepared by co-precipitation method. To obtain the desired nanocrystalline phase, the as prepared sample has been sintered at 700 °C for 6 h in an argon atmosphere. The crystallographic phase is confirmed by Rietveld analysis of the X-ray diffraction (XRD) pattern. The results of XRD analysis is also in agreement with those obtained from high resolution transmission electron microscopy (HRTEM) and Raman spectra of the sample. The results of XRD, HRTEM and Raman spectra confirmed that all Fe ions are successfully doped in the lattice of europium oxide. Also, no impurity phase has been formed in the sample. Hysteretic behavior in the magnetization versus applied field curve confirmed the presence of ferromagnetic ordering of Eu 1.90 Fe 0.10 O 3− δ at room temperature. The ferromagnetism is attributed to the substitution of Fe-ions in Eu 2 O 3 , which is successfully explained by the bound-magnetic-polaron model.

It is tried to empirically understand the superconducting critical temperature Tc of various materials (24 elements, 286 AnB (n = 1, 2, 3) compounds, 34 Fe- and 49 Cu-based compounds) by the effective pseudopotential radius, r(eff), and the effective orbital electronegativity, χ(eff)(=[N(v)/r(eff)]1/2). By giving the sets of values of r(eff) and the number of effective electron, N(v), for 65 elements under the assumption that both the hybridization state and N(v) can be assigned to 65 elements in advance by considering their electronic characters, the Tc/N(atom)–χ(eff) and Tc–N(v)r(eff)3 relations are examined, where N(atom) is the number of atom in compounds. It is found that a convex triangle-like relation is obtained between Tc/N(atom) and χ(eff) and the maximum of Tc/N(atom) is observed at around the threshold χ(eff) corresponding to metal–semiconductor transition. The cuprates and Fe-compounds with the χ(eff) closer to the threshold value show the higher Tc value. Applying the linear relation between Tc and N(v)r(eff)3 empirically obtained for the elements to the compounds, it is indicated that about two-thirds of AnB compounds as well as the Fe- and Cu-based compounds are well placed along the linear relation. These results allow us to estimate the Tc value in compound materials empirically based on the effective pseudopotential radius determined by the assumed hybridization.

Alkali and alkali earth hydrides have been used as solid state reductants recently to yield many interesting new oxygen-deficient transition metal oxides. These reactions have tacitly been assumed to be a solid phase reaction between the reductant and parent oxide. We have conducted a number of experiments with physical separation between the reductant and oxides, and find that in some cases reduction proceeds even when the reagents are physically separated, implying reactions with in-situ generated H{sub 2} and, to a lesser extent, getter mechanisms. Our findings change our understanding of these topochemical reactions, and should enhance the synthesis of additional new oxides and nanostructures. - Graphical abstract: Topochemical reductions with hydrides: Solid state or gas phase reaction? Display Omitted - Highlights: • SrFeO{sub 2} and LaNiO{sub 2} were prepared by topochemical reduction of oxides. • Separating the reducing agent (CaH{sub 2}, Mg metal) from the oxide still results in reduction. • Such topochemical reactions can occur in the gas phase.

Two dimensional diagrams for superconducting elements and AnB(n = 1, 2, 3) compounds have been constructed using the difference (ΔrENav) between Zunger’s pseudopotential radii and the orbital electronegativity ( [ ( Z / r ( s n p m ) ) 1 / 2 ] ENav ) derived from the pseudopotential radii. It is found that both superconducting elements and AnB compounds are well placed in the same domain surrounded by four boundary lines in the Δ r ENav - [ ( Z / r ( s n p m ) ) 1 / 2 ] ENav diagram. For sp-bonded elements, the boundary for superconducting/non-superconducting (SC/non-SC) is determined by a constant orbital electronegativity of [ ( Z / r ( s n p m ) ) 1 / 2 ] ENav ≅ 2.3 , which is close to the boundary ( [ ( Z / r ( s n p m ) ) 1 / 2 ] ENav = 2.046 ) for the metal–semiconductor transition. Superconducting elements and compounds with relatively high Tc values have an orbital electronegativity close to the value ranging between SC/non-SC and metal–semiconductor transition boundaries. It is suggested that arithmetically averaging of electronegativity is inadequate in AB-type transition metal nitrides and carbides.

In order to elucidate the details of successive magnetic transitions in the rare earth cobalt arsenic oxides ( RE CoAsO), we have measured muon-spin rotation and relaxation( μ + SR) spectra of powder samples with RE = La, Ce, Pr, Nd, Sm, and Gd. Together with the result of magnetization measurements, it was found that all the compounds enter into abulk static ferromagnetic ordered phase below around 70 K(= T C ). Furthermore, additional transitions into a static antiferromagnetic ordered phase were found for the RE = Nd, Sm, and Gd compounds; namely T N1 = 15 K and T N2 = 7 K for Nd, T N1 = 41.5 K and T N2 = 17.5 K for Sm, and T N = 3K for Gd.

In order to clarify the carrier density dependence of the microscopic magnetic nature in Na x CoO 2 * y H 2 O, we have performed a μ + SR study of H 2 O and D 2 O absorbed samples. Based on the ZF- μ + SR measurements, there was no clear difference between the two superconducting phases (SCI and SCII). This is also likely to exclude the exotic scenario for the superconductivity of the SCII phase, in which the superconducting state breaks the time-reversal symmetry of the Cooper pairs, resulting in the appearance of a weak internal magnetic field below T c . Furthermore, the ZF-spectrum for the H 2 O absorbed sample exhibits a clear oscillation in the whole T range measured (1.4-100 K), suggesting the formation of “[H 3 O] + -like” H 2 μ + O ions in the sample. The absence of the oscillation in the D 2 O absorbed sample also evidences the presence of the H 2 μ + O complex. Considering the fraction of the H 2 μ + Osignal, we have demonstrated the coexistence of [H 3 O] + ions and H 2 O in this compound. Finally, the muonic Knight shift measurements suggested the change in electronic state around 10 K and 40 K for the SCI and SCII samples.

We will present the synthesis, structure and magnetic properties of a new quadruple-layered perovskite (CuCl)Ca{sub 2}NaNb{sub 4}O{sub 13}. Through a topotactic ion-exchange reaction with CuCl{sub 2}, the precursor RbCa{sub 2}NaNb{sub 4}O{sub 13} presumably having an incoherent octahederal tliting changes into (CuCl)Ca{sub 2}NaNb{sub 4}O{sub 13} with a 2a{sub p} Multiplication-Sign 2a{sub p} Multiplication-Sign 2c{sub p} superstructure (tetragonal; a=7.73232(5) A, c=39.2156(4) A). The well-defined superstructure for the ion-exchanged product should be stabilized by the inserted CuCl{sub 4}O{sub 2} octahedral layers that firmly connect with neighboring perovskite layers. Magnetic studies show the absence of long-range magnetic ordering down to 2 K despite strong in-plane interactions. Aleksandrov Prime s group theory and Rietveld refinement of synchrotron X-ray diffraction data suggest the structure to be of I4/mmm space group with in-phase tilting along the a and b axes, a two-tilt system (++0). - Graphical Abstract: We present a quadruple-layered copper oxyhalide (CuCl)Ca{sub 2}NaNb{sub 4}O{sub 13} synthesized through a topotactic ion-exchange reaction of RbCa{sub 2}NaNb{sub 4}O{sub 13} with CuCl{sub 2}. The compound has a well-defined superstructure. Magnetic studies suggest the absence of magnetic order even at 2 K. Highlights: Black-Right-Pointing-Pointer (CuCl)Ca{sub 2}NaNb{sub 4}O{sub 13} was prepared by ion-exchange reaction of RbCa{sub 2}NaNb{sub 4}O{sub 13} with CuCl{submore » 2}. Black-Right-Pointing-Pointer Compound has a 2a{sub p} Multiplication-Sign 2a{sub p} Multiplication-Sign 2c{sub p} superstructure (tetragonal; a=7.73 A, c=39.21 A). Black-Right-Pointing-Pointer Such a well-defined superstructure was not observed in the precursor compound. Black-Right-Pointing-Pointer Aleksandrov Prime s theory and Rietveld study suggest a (++0) octahedral tilting (I4/mmm). Black-Right-Pointing-Pointer Magnetic studies revealed the absence of magnetic order down to 2 K.« less

Magnetic nanoparticles of FePt intermetallic compound were formed in molten LiCl–KCl–CsCl electrolyte under 1 atm of Ar atmosphere by plasma-induced cathodic discharge electrolysis. By utilizing the displacement reaction between the Fe(0) and Pt(II), FePt intermetallic compound nanoparticles were obtained from the melt. The displacement reaction produced small primary particles that considerably aggregated to form larger secondary particles. The coercivity of the obtained FePt intermetallic compound nanoparticle increased with a longer residence time in the melt. The coercivity of the FePt intermetallic compound nanoparticle obtained after a residence time of 3 h was measured to be 199 mA m −1 . FePt intermetallic compound nanoparticles could also be obtained by the co-depositing Fe and Pt from Fe(II) and Pt(II) in the melt. In this case, the primary particle size distribution became broader, but the aggregation of primary particles was suppressed. The coercivity of the obtained FePt intermetallic compound nanoparticles showed a quite high value of 245 mA m −1 that did not depend on the residence time.

The influence of composition on the structural ordering and magnetism in the V x Nb 1+ y S 2 system has been investigated by X-ray diffraction and magnetic measurements. Stoichiometric V 1/3 NbS 2 did not exhibit the structural ordering of vanadium between the NbS 2 layers. In the ordered structure, the vanadium composition deviated from the ideal value of x = 1 3 to both higher and lower values, while the niobium composition was in the range of 0.05⩽ y ⩽0.18. Excess niobium, y >0, is thought to play an essential role in the structural ordering in this system. For samples with excess niobium and ordered structures, a magnetic transition was observed at 20–50 K, depending on the composition. The spontaneous magnetization of 3–5×10 −3 μ B /V atom is thought to be intrinsic to this system. The magnetization curves consisted of a constant and a proportional parts of the magnetic field, which correspond to the spontaneous magnetization and high-field susceptibility, respectively. The magnetization curves and the temperature dependencies of the high-field susceptibility were quite similar to those of the canted antiferromagnetic NiS 2 . A correlation between the structural and magnetic ordering is suggested.

We found two components of the in-plane Co 59 NMR Knight shift K and different nuclear spin–lattice relaxation rates 1 / T 1 in bilayer hydrated superconductor Na x CoO 2 · y H 2 O , an oriented powder sample by a magnetic field in Fluorinert FC70. Distinguishable two peaks in the central transition line of the Co 59 NMR spectrum at 10 K can be explained by an anisotropic Knight shift in a triangular plane. The hyperfine coupling constants seem to change around 150 K, in which the bulk susceptibility χ shows a broad minimum, suggesting a change of the electronic state in the CoO 2 plane.

A transition metal-radical heterospin complex [Ni(salox) 2 (IM4Py) 2 ] ( 1 ) (salox = salicylaldoxime, IM4Py = 2-(4′-pyridinyl)-4,4,5,5-tetramethylimidazoline-l-oxyl) ( 1 ) has been synthesized based on the substitution reaction of Ni(salox) 2 (py) 2 and IM4Py. Compound 1 exhibits a chain structure created by the intermolecular hydrogen bonds. Magnetic measurements show intermolecular antiferromagnetic interactions in 1 .

Thin films of Co2MnSn were prepared on MgO(0 0 1) substrates with a Cr-buffer layer from three elemental targets by ultrahigh-vacuum alternate deposition. These films showed good crystallinity, and the epitaxial relations were found to be MgO(0 0 1)//Cr(0 0 1)//Co2MnSn(0 0 1) and MgO[1 0 0]//Cr[1 1 0]//Co2MnSn[1 1 0]. [Co2MnSn(2.2 nm)/Cr(0.9 nm)]10 multilayers were also prepared with high crystallographic quality. The magnetic properties of Co2MnSn films were studied by magnetization measurements and 119Sn Mossbauer spectroscopy. Hyperfine fields observed by Mossbauer effect measurements showed that the degree of short range order around Sn in the samples grown at 200 ∘ C was as good as that in bulk samples.

A Prussian-blue analogue Mn 3 [Cr(CN) 6 ] 2 ·12H 2 O has been prepared and characterized by single crystal X-ray analysis and magnetic measurements. The complex has a disordered face-centered cubic lattice and shows two magnetic transition temperatures of 74 and 61 K.

A novel copper(II)-radical complex [Cu(NITmPy)(PDA)(H2O)] · (H2O) (1) (NITmPy = 2-(3′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, H2PDA = 2,6-pyridinedicarboxylic acid) has been synthesized and structurally characterized by X-ray diffraction methods. It crystallizes in the triclinic space group P 1 ¯ . The Cu(II) ion exists in a distorted square pyramid environment. The molecules of [Cu(NITmPy)(PDA)(H2O)] · (H2O) are connected as a two-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show intramolecular ferromagnetic interactions between NITmPy and Cu(II) ion and intermolecular antiferromagnetic interactions in 1.

Combined with pulsed magnets, we have carried out X-ray diffraction experiments under magnetic fields above 30 T. A key technique is that we employed a very small pulsed magnet, which is readily included in a conventional X-ray diffraction system because of the small size, small required energy, and small heat production. The insulator-to-metal transition of Pr0.6Ca0.4MnO3 around 9 T and the valence transition of YbInCu4 around 26 T are shown as demonstrations.

The physical properties of the rare-earth metal diselenides RS e2− x and rubidium intercalated gadolinium triselenide Rb x GdSe 3− y were investigated. The resistivity and the electron diffraction scattering measurements of RS e2− x revealed that the energy gaps of these semiconductive compounds are related to the presence of the superstructures due to distortion of the Se-layer. All magnetic RS e2 and Rb x GdSe 3− y show antiferromagnetic transition. The anisotropy of the magnetic moment in RSe 2− x and Rb x GdSe 3− y originates in the single ion anisotropy of the rare-earth metal while the direction of magnetic moment in the ordered state originates also in the single ion anisotropy in the case of RS e2− x but in the dipolar interaction in Rb x GdSe 3− y .

A selenate analogue of sodium Jarosite NaFe 3 (SeO 4 ) 2 (OH) 6 has been synthesized by precipitation from aqueous solution. We have newly determined the structural parameters by powder X-ray diffraction refinement. The structure is similar to that of sulfate Jarosite analogues, while the unit cell volume is larger. The temperature dependence of the magnetic susceptibility shows a cusp-like anomaly at 45 K, and the spontaneous magnetization appears below 33 K. We have measured the Mossbauer spectra of 57 Fe 3+ ( S =2/5) ions, and revealed an anomalous fluctuation of the hyperfine field.

We report a 205 Tl NMR study of vortex state for an oriented polycrystalline sample of an overdoped high- T c superconductor Tl 2 Ba 2 CuO 6+δ ( T c ∼85 K) with magnetic field 2 T along the c -axis. An obvious Redfield pattern of the 205 Tl NMR spectrum for our sample at T =5 K indicates the vortex lattice state without local antiferromagnetic order at vortex cores. We emphasize that nonexponential nuclear spin-lattice relaxation curves indicate an imperfect vortex lattice or Bragg glass phase.

High-field ESR technique has been applied to the novel frustrated spin chain system KCu5V3O13, to reveal the peculiar ground state proposed by the previous results of the magnetic susceptibility and the magnetization measurements. We successfully observed the antiferromagnetic resonance with the easy axis type anisotropy below 7 K . In addition, small shifts of the resonance field probably due to the re-arrangements of spin configuration in the ordered phase were also observed at about 4 K in the detailed temperature dependence measurements. This result confirmed the observation of double peaks at 3.9 and 7 K in the specific heat measurements performed in advance to the high-field ESR measurements. We will discuss about the ground state of KCu5V3O13 based on these results together with those obtained in the KMgCu4V3O13, where no antiferromagnetic resonance was observed.

The magnetic and transport properties have been investigated by means of magnetization and resistivity measurements for EuSr 2 RuCu 2 O 8 compound. It is shown that EuSr 2 RuCu 2 O 8 compound exhibits ferromagnetic order of Ru moments below T c =130.2 K and becomes superconducting at T c =10 K. The fact that the magnetization increases with increasing external magnetic field and does not show the saturation even at the highest applied field 42 T indicates that the magnetic order in this compound is an itinerant-electron ferromagnetic. It is estimated that Ru exists in a mixed valance state (near Ru 4.8+ ) between Ru 4+ and Ru 5+ in this compound from the estimated saturation moment value. We have discussed the ferromagnetic order by the viewpoint of a band model.

The magnetic properties of Ca 3 FeRhO 6 , which is isostructural with the rhombohedral K 4 CdCl 6 -type structure, were investigated by magnetic susceptibility and high-field magnetization measurements using field-oriented samples and 57 Fe Mossbauer spectroscopy using a powder sample. We observed anisotropy in the magnetic susceptibility below 12 K and the spin–flop transition in the magnetization curve at 4.2 K. The 57 Fe Mossbauer spectra show that the Fe ions occupy the trigonal prism site in the trivalent state with the high-spin configuration. It has been confirmed from our investigations that Ca 3 FeRhO 6 orders below 12 K antiferromagnetically with the strong magnetic anisotropy along the c -axis. The quantitative analysis suggests that the Rh ions occupy the trigonal prism site partially in place of the Fe ions.

We make the first report that a metallic pyrochlore oxide \Cd2Re2O7, exhibits type II superconductivity at 1.1 K. The pyrochlore oxide is known to be a geometrical frustrated system, which includes the tetrahedral network of magnetic ions. A large number of compounds are classified in the family of pyrochlore oxides, and these compounds exhibit a wide variety of physical properties ranging from insulator through semiconductor and from bad metal to good metal. Until now, however, no superconductivity has been reported for frustrated pyrochlore oxides. The bulk superconductivity of this compound is confirmed by measurements of the resistivity and the a. c. magnetic susceptibility. The \Hc2, which is extrapolated to 0 K, is estimated as about 0.8 T, using the resistivity measurements under aplied field. The plot of \Hc2 vs $T$ indicates that the Cooper pairs are composed of rather heavy quasiparticles. This fact suggests that frustrated heavy electrons become superconducting in this compound., 8 pages, submitted to Jounal of Physics: Condensed Matter

The copper-ruthenium oxide, EuSr 2 RuCu 2 O 8 has been studied by means of nuclear magnetic resonance (NMR) and nuclear spin-lattice relaxation rate (T -1 1 ) measurements. This compound shows the ferromagnetic-like transition at T M ∼ 130 K and the superconducting transition at T onset ∼ 30 K. 99,101 Ru NMR signals under zero applied field have been observed at high frequencies around 60 MHz and around 130 MHz, both of which could be identified as ferromagnetic resonances even below T onset c . These frequency-swept spectra around 60 MHz and around 130 MHz are ascribed to 99,101 Ru nuclei of Ru 4+ (S = 1) and to those of Ru 5+ (S = ), respectively. The nuclear spin-lattice relaxation rate T -1 1 for 101 Ru nuclei decreases just below T onset c due to the formation of a superconducting gap. Our NMR results are supported microscopically that coexistence of the ferromagnetism and superconductivity is realized in this compound.

The specific heat of LuCu5−xAgx reference samples was measured to reanalyse the heavy-fermion behaviour of the isostructural AuBe5-type cubic system YbCu5−xAgx with x=0–1 which is a series of dense Kondo compounds whose characteristic temperature T0 decreases as x decreases. For YbCu5−xAgx, the γ-value increases from 210 mJ / mol K 2 for x=1.0 to 550 mJ / mol K 2 for x=0.0. The analysis of the magnetic susceptibility and of the magnetic contribution to the specific heat in terms of Coqblin–Schrieffer (CS) model reveals a significant reduction of the effective ground state degeneracy: While YbCu4Ag is well described by the CS model with J= 7 2 and T 0 =150 K , one has to consider a crystalline electric field splitting of the Yb3+ ground state multiplet with an energy scale of the order of 80 K and a Kondo contribution corresponding to the CS model with J= 3 2 and T 0 ∼30 K in the case of YbCu5, i.e. there is a cross-over of the characteristic energy scales of the Kondo interaction and of the CEF splitting within the series Yb(Cu,Ag)5.

We report magnetic properties of CuSb 2− x Ta x O 6 with tri-rutile type structure. Solubility limit was determined to be x =1.0 by the solid-state reaction and X-ray diffraction measurements. The value of J , the magnetic interaction obtained by Bonner–Fisher fitting, was found to decrease gradually with Ta content x . The value of T N also decreases with x and seems to be zero at x =0.6. As a result of our structural analysis, this fact shows the crossover from one-dimensional to two-dimensional magnetic system with a local distortion caused by Ta substitution. Although the ground state of the compound with x >0.6 is not clear, it can be considered that the long-range antiferromagnetic order disappears and that the quantum critical regime such as a spin-singlet state is realized in this system.

We synthesized the powder samples of KMgxCu5−xV3O13 (x=0.1∼1) and investigated their magnetic susceptibilities and the magnetization curves up to 47 T. The Curie constant and the Weiss temperature of KMgCu4V3O13 change markedly around 20 K. From the Curie constant estimated from the data between 5 and 10 K, the number of spins in the low-temperature region was estimated to be nlow=8.13%, assuming all the copper spins have S=1/2 and g=2. The magnetization curve of KMgCu4V3O13 at 1.7 K is bent around 20 T and shows a linear increase between 20 and 30 T. The magnetization, Mlinear(H→0), estimated by extrapolating the linear part to 0 T is 0.306μB/f.u. Furthermore, all the x dependences of the Neel temperature TN, nlow, θlow, the magnetic field at spin–flop transition Hsf and Mlinear(H→0) change continuously with x. This indicates that there is no quantum critical region between the frustrated spin chains of KCu5V3O13 and KMgCu4V3O13. The ground states of KCu5V3O13 and KMgCu4V3O13 have been deduced.

The magnetic susceptibility and the 63,65 Cu nuclear quadrupole resonance have been measured in the quasi-one-dimensional cuprate Ca 0.85 CuO 2 which contains edge-sharing CuO 2 chains separated by Ca layers. The behaviors of the magnetic susceptibility and the 63 Cu nuclear spin–lattice relaxation rate are well explained by assuming the coexistence of an antiferromagnetic ordering and spin gap states which can be realized in the hole doped 1D Cu–O chain.

Pure and Yb-site partially substituted by Y, Lu and Zr samples of YbInCu 4 were synthesized. Temperature dependence of magnetic susceptibility from 2 to 300 K under 0.5 T and high field magnetization up to 41 T at 4.2 K were measured. We found that both transition temperature ( T v ) and transition magnetic field ( H v ) of YbInCu 4 are shifted to lower temperatures and lower magnetic fields by Y or Lu substitution, while they are increased by Zr substitution. The chemical pressure effect and dense Kondo interaction are discussed as factors to influence the valence transition of YbInCu 4 .

51 V nuclear magnetic resonance and relaxation are reported for the Hollandite Bi 1.77 V 8 O 16 system. Bi x V 8 O 16 having the Hollandite structure with 1.6 x x T 1 of 51 V NMR to investigate the magnetic and electric properties of Bi 1.77 V 8 O 16 , which will provide information on the electronic states below and above the MIT temperature T MIT in this system. Above T MIT , the temperature dependence of 1/ T 1 T obeys a modified Korringa relaxation with a large correlation factor K ( α )=3.2, implying that the antiferromagnetic spin fluctuations are dominant in the metallic regime of the present system.

The structure, magnetization and electrical resistance for the La2-xSrxMnRuO6 system with double-perovskite structure were investigated. The structural transition from an orthorhombic cell with a random arrangement of Mn and Ru to a cubic cell (rock salt sublattice) with an ordered arrangement occurs at near x=1.0. All samples La2-xSrx MnRuO6 (0 less than or equal tox less than or equal to2.0) show semiconducting behavior. The conductivity for the samples with x less than or equal to0.3 at higher temperature has a 2-dimensional variable-range-hopping (VRI-I) mechanism. Bur the temperature dependence of resistance for La2-xSxMnRuO6 (1.0 less than or equal tox less than or equal to2.0) samples can be described using neither a VRH mechanism nor a thermal activation mechanism in a single energy gap. The samples with x s less than or equal to2.0) samples show ferromagnetism below 300 K. The molecular field constant radio N-AB/N-AA changes with the doping concentration of Sr for La. (C) 2001 Elsevier Science B.V. All rights reserved.

Temperature and magnetic field variations of the electric resistivitiy ( ρ ) as well as temperature dependence of the magnetic susceptibility ( χ ) are reported for the YbCu 5− x Au x system with the C15b-type structure. These results indicate a systematic composition dependence from dense Kondo to RKKY antiferromagnetic system via quantum critical point with x =0.2–0.4. The logarithmic temperature dependence of ρ was observed in the middle temperature range for all the compositions, implying that the incoherent Kondo scattering is dominant in this T-region. With decreasing temperature, the ρ tends to saturate, makes a maximum, then decreases toward the Fermi liquid ground state due to the coherent dense Kondo effect ( x x >0.4). The non-Fermi liquid behavior was observed around the quantum critical composition ( x =0.2–0.4).

Physical properties of the heavy-fermion system YbCu5 and the YbCu5−xAgx compounds are studied in high magnetic fields. These systems show metamagnetic-like behavior at low temperature. This can be qualitatively explained by the Bethe-ansatz solution of the Coqblin–Schrieffer model. A large negative magnetostriction is observed in YbCu5 at low temperature, which indicates a valence change of Yb by field: from the valence-fluctuating state with itinerant 4f-electrons at low field to a stable Yb3+ state with localized magnetic moments at high field.

In order to clarify the variation of the microscopic magnetic nature with the carrier density in Na x CoO 2 · y H 2 O , we have measured positive muon-spin rotation/relaxation ( μ + SR ) spectra for H2O as well as D2O absorbed samples. Based on the zero field (ZF-) μ + SR measurements, there was no clear difference between the two superconducting phases (SC-I and SC-II). Furthermore, the ZF-spectrum for the H2O absorbed sample exhibits a clear oscillation in the whole T range measured (1.4–100 K), suggesting the formation of “[H3O]+-like” H2μ+O ions in the sample. Further, the absence of an oscillation in the D2O absorbed sample also evidences the presence of H2μ+O. We also measured 59Co nuclear quadrupole resonance spectra of magnetic sample. The temperature dependence of spectra shows that there is no evidence of charge ordering and CDW ordering around magnetic transition temperature.

The magnetization of V 5 S 8 and V 5 Se 8 was measured in pulsed high magnetic fields up to 39 T. The anomalies were observed in the magnetization curves for both V 5 S 8 and V 5 Se 8 . For V 5 S 8 , the anomaly at lower field is thought to correspond to spin flopping. The magnetization curves exhibited saturation for both compounds and the values of the ordered moments for V 5 S 8 and V 5 Se 8 were estimated to be 1.5 and 1.2 μ B /V I from the saturation moments, respectively. Our results support the magnetic structure of V 5 S 8 proposed by neutron diffraction measurements.

One-dimensional compounds Ca3CoRhO6 and Ca3FeRhO6 have been newly synthesized and structurally characterized by Rietveld refinement of powder X-ray diffraction data. Both compounds are isostructural with the rhombohedral K4CdCl6-type structure (space group R 3 c; Z=6; Ca3CoRhO6: a=9.2017(1) A, c=10.7296(1) A Ca3FeRhO6: a=9.1960(1) A, c=10.7861(1) A). The structure of Ca3CoRhO6 and Ca3FeRhO6 contains one-dimensional chains consisting of alternating faced-sharing CoO6, FeO6 trigonal prisms, and RhO6 octahedra, respectively. The magnetic susceptibility of Ca3CoRhO6 exhibits an abrupt drop at 35 K, which is also observed in Sr3NiIrO6 and Ca3CoIrO6. Ca3FeRhO6 is an antiferromagnet with TN=12 K.

We have investigated the physical properties of Pb 2 - x Ln x Ru 2 O 7 - δ ( Ln = Sm , Eu ) compounds with pyrochlore crystal structure. The solid-solution compounds of Pb 2 - x Ln x Ru 2 O 7 - δ show from metallic ( x = 0 ) to insulating ( x = 2 ) behaviors. These compounds with x > 1.0 also indicate the spin-glass like behaviors at low temperature ( T T SG ) which are attributed to the geometrical frustration on pyrochlore lattice. The transition temperature T SG decreases monotonously with decreasing x and goes to zero at x = 0.6 . The sample with 0.4 ⩽ x ⩽ 0.8 shows the metal–insulator (MI) transition at 10–30 K where the sign of temperature derivative of electric resistivity changes.

We have studied electronic structures of VO 2 by soft and hard X-ray synchrotron core-level photoelectron spectroscopy. In our measurements, temperature and photon energy dependences of the V 2p core-level spectra are observed. Remarkable spectral changes are observed across the metal-insulator transition (MIT) at T = 340 K . A clear shoulder structure is observed on the lower binding energy side of the V 2 p 3 / 2 peak in the metallic phase. This shoulder structure, being stronger for larger h ν , is interpreted as the well-screened feature by bulk conduction electrons.

We studied magnetic excitations of a spin-gapped compound Na 2 Cu 2 TeO 6 , the hole doping effect on the Cu 2 TeO 6 plane via topotactic Na deficiency introduced by soft-chemical treatment, the spin vacancy effect by Zn substitution and the magnetic impurity effect by Ni substitution for Cu by means of magnetic susceptibility measurements. It turned out that unpaired moments of the doped holes by Na deficiency, Zn and Ni impurities induce Curie magnetism and lower the broad maximum temperature T max in the uniform spin susceptibility. The decrease of T max indicates the decrease of a predominant superexchange interaction.

Pb 2 V 3 O 9 is an S = 1 2 alternating spin chain compound with a spin-gap. We have observed field- and impurity- induced antiferromagnetic long range order (AF-LRO) in this system. We made phase diagrams for each case from the temperature dependence of magnetic susceptibility χ measurement. For both perturbation induced AF-LRO, the increase of T N was commonly observed in the low magnetic field and the low impurity concentration regions. However, the behavior of χ below T N for each case is quite different; one increases and the other decreases. These contrastive behaviors originate from spatially different characters of the induced moments by the perturbations introduced to the spin-gap system.

We have studied the synthesis and physical properties of misfit cobaltates compounds intercalated by the iodine. The iodine atoms was successfully intercalated into the misfit cobaltates by the heat treatment at a constant iodine partial pressure. In the case of Bi(Pb)–Sr–Co–O system, I α Bi 2 - x Pb x Sr 2 Co 2 O y , it was found that the c -axis drastically increased by the intercalation. The iodine content α was determined to be 0.97 for Pb content x = 0 , and 0.81–0.85 for x > 0.4 . From magnetic and electric measurements for these compounds, it was suggested that the intra-layer couplings between CoO 2 layers are probably reduced by the iodine intercalation.

High resolution synchrotron X-ray diffraction methods have been used to study the crystal structure of the two-dimensional square-lattice antiferromagnets ( CuCl ) LaNb 2 O 7 and ( FeCl ) LaNb 2 O 7 . While the structure of the former is of tetragonal symmetry with simple perovskite unit cell dimensions in the a , b plane ( a × a ) , the latter exhibits a tiny orthorhombic distortion with a 2 a × 2 a × c superstructure, providing a first example of modulation in the family of transition-metal oxyhalides prepared from topotactic ion-exchange reactions. Possible arrangement in the FeCl layer is proposed.

High field ESR measurements have been performed on newly synthesized layered manganese oxides A 4 Mn 3 O 10 (A=Ba, Sr) using a pulsed magnetic field up to 16 T. From the temperature and the frequency dependence measurements, it was confirmed that both ground states at low temperature are the antiferromagnetic ordered state. The typical AFMR absorption lines were observed for both compounds and both were well explained by the AFMR theory for a two-sublattice antiferromagnet with orthorhombic magnetic anisotropy. Moreover, we found that the magnetic anisotropy energies in these compounds are very small as compared with their exchange interactions.

New one-dimensional compounds Ca3CoBO6(B=Ir, Ru) with K4CdCl6-type structure have been synthesized by conventional solid state reactions. Both compounds adopt the rhombohedral symmetry with the space groupR 3 c;a=9.1811(1) A,c=10.8232(3) A,Z=6 (hexagonal expression) for Ca3CoIrO6anda=9.1921(3) A,c=10.7784(7) A,Z=6 for Ca3CoRuO6. One-dimensional chains are built by alternating face-shared CoO6octahedra andBO6trigonal prisms. The magnetic susceptibility of Ca3CoIrO6shows an abrupt drop at 30 K, as seen in the case of Sr3NilrO6, suggesting that ferromagnetic chains couple antiferromagnetically. On the contrary, Ca3CoRuO6is an ordinary antiferromagnet withTN=55 K. We have also succeeded in preparing the solid solution series, Ca3Co1+xIr1−xO6and Ca3Co1+xRu1−xO6(0≤x≤1), and magnetic properties of these systems were investigated.