The electrical and magnetic properties of lanthanide alkaline-earth transition-metal oxides

Five Ln(2)SrMCuO(6.5) oxides (M = Co, Ln = Y and Ho; M = Fe, Ln = Y, Ho, and Dy) were synthesized, and their crystal structures, IR spectra, and physical properties were studied. They have almost the same structure and crystallize in orthorhombic systems. Below room temperature, Y2SrFeCuO6.5, a known layered oxide, shows antiferromagnetic behavior, but the four new oxides are paramagnetic. Y2SrFeCuO6.5 fits the Curie-Weiss law in the temperature range 300-100 K, but Y2SrCoCuO6.5 shows complex magnetic behavior because of the disproportion of some Co+3 to Co+2 and Co+4 The five oxides are all p-type semiconductors in the measured temperature range and have large electrical resistivities at room temperature.

Structural and magnetic properties of (PrxSm1-x)Mn2Si2

Crystallographic and magnetic properties of intermetallic compounds (PrxSm1-x) Mn2Si2 (x = 0 similar to 0.80) have been investigated by X-ray powder diffraction, XPS and magnetic measurements. All the compounds crystallize in ThCr2Si2-type structure. Substitution of Pr for Sm leads to the increase of the lattice constants and the transition from antiferromagnetism (AFM) to ferromagnetism (FM). The valence-fluctuation in the compounds was observed and the relation between the change of electron binding energy and magnetic properties was also discussed preliminarily.

Structure, electric and magnetic properties of new compounds CdYMWO7 (M = Cr and Mn)

Two new compounds with the formula of CdYMWO7 (M = Cr, Mn) were prepared by solid state reaction. They crystallized with orthorhombic structure with the cell parameters of a = 11.7200 Angstrom, b = 7.1779 Angstrom, c = 6.9805 Angstrom (CdYCrWO7), and a = 11.7960 Angstrom, b = 6.1737 Angstrom, c = 7.6530 Angstrom (CdYMnWO7). These compounds are insulators with high resistivities at room temperature. The temperature dependence of the magnetic susceptibility of CdYMWO7 (M = Cr and Mn) show Curie-Weiss Law's behaviors from 80 to 300 K. The magnetic moments at room temperature fit very well with those corresponding to Cr3+ and Mn3+ ions. This suggests that both Cr and Mn ions exist in + 3 oxidation state in CdYMWO7 compounds. (C) 1998 Elsevier Science Ltd. All rights reserved.

Structure, luminescence and magnetic properties of AgLnW(2)O(8) (Ln = Eu, Gd, Tb and Dy) compounds

Four new compounds AgLnW(2)O(8) (Ln = Eu, Gd, Tb and Dy) are prepared by solid-state reactions. They crystallize with a scheelite-related monoclinic symmetry. Infrared (IR) spectra show complicated absorption transitions in the region of 1000-400 cm(-1) that are similar to those of AgLnMo(2)O(8). Broad excitation and emission bands of the tungstate group are observed in AgGdW2O8 and AgTbW2O8 with a large Stokes shift, 12 573 and 12 387 cm(-1), respectively. Excitation and emission spectra of AgLnW(2)O(8) (Ln = Eu, Gd and Tb) show that energy transfer from the tungstate to EU3+, Gd3+ and Tb3+ occurs and that Eu3+ ions occupy a single crystallographic site with the C-2 Site symmetry. (C) 1997 Elsevier Science Ltd. All rights reserved.

Synthesis, luminescence and magnetic properties of YGa3-xCrxB4O12

The synthesis temperature of YGa3B4O12 and the effect of the synthesis temperature and chromium doping on the luminescence properties were studied. YGa3-xCrxB4O12 were synthesized and their magnetic properties were described. Results show that the fluorescence intensity increases with the increasing of synthesis temperature. The structure of compounds was stabilized, and their emission spectra were changed when small quantity of chromium was doped in. The magnetic susceptibilities increase with the increasing of Cr3+ concentration.

Synthesis, crystal structure and magnetic properties of a series of polymeric lanthanoid-copper complexes [Ln(2)Cu(3){O(CH2-CO2)(2)}(6)].nH(2)O (Ln=La, Nd, n=9; Ln=Er, n=6)

The reaction of diglycolic acid, O(CH2CO2H)(2), with Cu(NO3)(2) . H2O and lanthanoid nitrate hydrate produces a series of novel Ln-Cu mixed metal complexes, [Ln(2)CU(3){O(CH2CO2)(2)}(6)]. nH(2)O (Ln = La, Nd, n = 9; Ln = Er, n = 6), which have been characterized by elemental analysis, i.r. spectroscopy, magnetic measurements and X-ray crystallography. The Ln(3+) and Cu2+ ions are connected by the carboxylate groups of the ligands, resulting in the formation of a complicated network.

Studies on the synthetic, structural, electrical and magnetic properties of Ln(n)MCo(n)O(3n+1) (Ln=Sm, Gd; M=Sr, Ba; n=1,2)

Three new oxides Sm2SrCo2O7, Sm2BaCo2O7 and Gd2SrCo2O7 have been synthesized successfully by solid state reaction mathod. The X-Ray diffraction spectra show that they are all isostructural with Sr3Ti2O7, and Ln(2)SrCo(2)O(7)(Ln=Sm,Gd) crystallized in tetragonal system, Sm2BaCo2O7 in orthrhombic system. The Co-O bonds in CoO2 planes of Ln(2)SrCo(2)O(7) are shorter than those of LnSrCoO(4)(Ln=Sm, Gd), and so their delectrons are more delocalized and their electrical resistivities are smaller. The electrical resistivities versus temperature in the range 300 similar to 1100K showed that the five brides show the characters of weakly localized systems. In the lower temperature range, the magnetic behaviors of Gd2SrCo2O7 and GdSrCoO4 fit Curie-Weiss law well, and the magnetic exchange reaction in CoO2 sublattices of Gd2SrCo2O7 is ferromagnetic, but that of GdSrCoO4 is antiferromagnetic. The other three oxides with Sm3+ showed complex magnetic behaviors which is perhaps related with the complexity of Sm3+.

STUDIES ON THE SYNTHETIC, STRUCTURAL, ELECTRICAL, AND MAGNETIC-PROPERTIES OF THE NEW LAYERED OXIDES LN(2)MCO(2)O(7) (LN=SM, GD, M=SR, BA)

Three new oxides Ln(2)MCo(2)O(7) (Ln = Sm, Gd; M = Sr, Ba) have been synthesized in solid state reaction method. The powder X-ray diffraction spectra show that they are all isostructural with Sr3Ti2O7. The electrical resistivities in the temperature range 300-1100 K show that they are all semiconductors, and a transition to metals is observed at 1053, 1053, and 573 K for Sm2SrCo2O7, Gd2SrCo2O7, and Sm2BaCo2O7, respectively. The magnetic suspectivities of Gd2SrCo2O7 in the temperature range 300-673 K fit the Curie-Weiss law well. A plateau is observed in the curves of Sm(2)MCo(2)O(7) (M = Sr, Ba) which is attributed to the configuration state change of Co(III) from low spin to high spin. (C) 1995 Academic Press, Inc.

VALENCE STATE EQUILIBRIA BETWEEN COBALT AND MANGANESE IONS AND MAGNETIC-PROPERTIES OF LACO0.9MN0.1O3

According to the thermodynamic equilibria between the low spin state Co(III) (t2g6e(g)0) ion and the high spin state Co3+ (t2g4e(g)2) ion and between the cobalt and manganese ions with different valence state and spin state, an approximate semiempirical f

SPIN AND VALENCE STATE EQUILIBRIA OF COBALT AND MAGNETIC-PROPERTIES OF LACOO3

On the basis of the spin and valence state equilibria and superexchange interaction of the various cobalt ions in LaCoO3, an approximate semiempirical formula has been proposed and used to calculate magnetic susceptibilities of LaCoO3 over a wide temperature range (100-1200 K). The results indicate that there are thermodynamic equilibria between the low spin state Co(III) (t2g6e(g)0) ion, the high spin state Co3+ (t2g4e(g)2) ion, the Co(II) (t2g6e(g)1) ion and the Co(IV) (t2g5e(g)0) ion in LaCoO3. The energy difference between the low spin state Co(III) and the high spin state Co3+ is about 0.006 eV. The content of the low spin state Co(III) ion is predominant in LaCoO3 and the content of the high spin state Co3+ ion varies with temperature, reaching a maximum at about 350 K, then decreasing gradually with increasing temperature. At low temperature the contents of the Co(II) ion and the Co(IV) ion in LaCoO3 are negligible, while above 200 K the contents of both the Co(II) ion and the Co(IV) ion increase with increasing temperature; however, the content of the Co(II) ion always is larger than that of the Co(IV) ion at any temperature. These calculated results are in good agreement with experimental results of the Mossbauer effect, magnetic susceptibility and electrical conductivity of LaCoO3.

VALENCE AND MAGNETIC-PROPERTIES OF YSR2-XCAXV3O9-Y

Compounds YSr22-xCaxVO9-y have an orthorhombic symmetry. XPS results show that the vanadium ions exist in the mixing valence in the system. Temperature dependence of magnetic susceptibility represents the Curie-Weiss law. The valence state of vanadium obviously affects the magnetic properties of YSr2-xCaxV3O9-y. The system exhibits a paramagnetic behavior from 300K to 1073K.

INVESTIGATION OF THE ELECTRICAL AND MAGNETIC-PROPERTIES OF YSR2-XCAXV3O9-Y

All the members of the solid solution of YSr2-xCaxV3O9-y have the orthorhombic symmetry. Their electrical and magnetic properties have been studied. The magnetic susceptibility and electrical resistivity increase gradually with x. The system shows paramagnetic behavior both at 300 K and at 77 K. It is shown that a change of valence state of vanadium obviously affects the electrical and magnetic properties of the solid solution.

STUDIES ON THE ELECTRICAL AND MAGNETIC-PROPERTIES FOR LASR2-XCAXV3O9+/-Y

The electrical and magnetical properties of LaSr(2-x)Ca(x)V3O9 +/- y have been investigated. The compounds are antiferromagnetic. They show a metallic conduction other than semiconductivity. The trivalent and tetravalent vanadium ions coexist in the system. The magnetic susceptibility increases and the resistivity decreases at room temperature with the increase of x value. It is shown that the change of the valency state of vanadium obviously influences the electrical and magnetical properties of the system.

Effect of Rapid Thermal Annealing on the Structure and Magnetic Properties of Chemical Vapour Deposition Cobalt Layers

Future read heads in hard disc storage require high conformal coatings of metal magnetic layers over high aspect ratio profiles. This paper describes pioneering work on the use of MOCVD for the deposition of cobalt layers. While pure cobalt layers could be deposited at 400C their magnetic properties are poor. It was found that the magnetic properties of the layers could be significantly enhanced with an optimised rapid thermal anneal. This work was sponsored by Seagate Technology and led to a follow up PhD studentship on the co-deposition of cobalt and iron by MOCVD.