G. V. Bazuev

Synthesis and magnetic properties of incommensurate phases A4CuMn2O9 (A=Ca, Sr)

Abstract New complex oxides A4CuMn2O9 (A=Ca and Sr) belonging to the family of quasi-one-dimensional compounds A3n+3mA′nB3m+nO9m+6n (n=3, m=1) have been obtained by solid-phase synthesis from Ca and Sr carbonates and oxides CuO and MnO2. It was established that both oxides are incommensurate and can be characterized by two sublattices with the same a, but different c (c1 and c2) parameters. Their lattice parameters are a 9.195(2), c1 3.744(1), c2 2.580(1) A for Ca4CuMn2O9 and a 9.602(2), c1 3.940(1), c2 2.593(1) A for Sr4CuMn2O9. Magnetic susceptibility (χ) measurement results were interpreted with allowance for exchange-bound dimers Mn4+–Mn4+ and paramagnetic centers Cu2+. Magnetic measurements revealed the presence of calcium manganate CaMnO3 in Ca4CuMn2O9. The maxima on χ=f(T) dependences at 7.5 K (Sr4CuMn2O9) and 3.5 K (Ca4CuMn2O9) allowed us to surmise that the compounds in question have antiferromagnetic correlations.

Crystal structure and magnetic properties of a one dimensional complex oxide ca3nimno6

Abstract The results of structural refinements and magnetic properties of one-dimensional oxide Ca 3 NiMnO 6 are presented. The structure of Ca 3 NiMnO 6 was solved by Rietveld analysis of powder neutron date in space group R -3 c with a =9.1227(9) A, c =10.5811(17) A, z=6 (type of K 4 CdCl 6 ). Infinite chains of MnO 6 octahedra and (Ni,Mn)O 6 trigonal prisms sharing faces run parallel to the c axis. The chains are separated by Ca 2+ cations, which are located in a distorted square antiprismatic environment. Magnetic susceptibility obeys the Curie-Weiss law at 300–600 K with μ eff value 5.00 μ B consistent with the valence cationic combination Ni 2+ -Mn 4+ . Magnetic measurements display the antiferromagnetic ordering in Ca 3 NiMnO 6 at 16 K.

Preparation of MnCo2O4 whiskers and spheroids through thermal decomposition of Mn1/3Co2/3C2O4 · 2H2O

The mixed oxalate Mn1/3Co2/3C2O4 · 2H2O has been prepared in the form of whiskers 2–5 μm in diameter and up to 50 μm in length and spheroidal nanofiber arrays 20 μm in diameter using two different coprecipitation procedures. Thermal decomposition of this oxalate in air has led to the formation of MnCo2O4 particles very similar in morphology to their oxalate precursor. The materials have been characterized by chemical analysis, thermogravimetry, x-ray diffraction. IR spectroscopy, and scanning electron microscopy.

Synthesis and Magnetic Properties of LaSr 2 CoMnO 7

A new oxide phase LaSr2CoMnO7.00±0.05, a member of the Raddlesden-Popper homologous series An + 1BnO3n + 1 (n = 2), was synthesized, and its structure and magnetic properties characterized. The unit cell of this phase was indexed in terms of space group I4/mmm with the parameters a = 0.3831(2) nm, c = 2.0070(1) nm. The magnetic susceptibility as a function of temperature obeys the Curie-Weiss law in the range 250–350 K. At low temperatures, magnetic anomalies are observed due to the competition between antiferromagnetic and ferromagnetic ordering and spin-glass transition. The charge state of transition metals was ascertained proceeding from magnetic measurements and XANES spectra.

Synthesis of micro- and nanosized manganese oxides from hydrated manganese oxalates and products of their chemical modification with ethylene glycol

The reactions of ethylene glycol with manganese oxalates MnC2O4 · 2 H2O and MnC2O4 · 3H2O on heating in air were studied. At temperature below 100°C, ethylene glycol was found to displace water from oxalates to give a new solvate compound according to the reaction MnC2O4 · nH2O + HOCH2CH2OH = MnC2O4(HOCH2CH2OH) + nH2O↑. The crystals of the solvates retain the morphology of the initial oxalates, which is then inherited by the products of their thermolysis. Thus, thermolysis of MnC2O4 · 3H2O and MnC2O4(HOCH2CH2OH) having quasi-unidimensional structure gave Mn3O4 and Mn2O3 nanowhiskers in air and MnO in an inert gas environment. Heating of MnC2O4 · nH2O in ethylene glycol at temperatures above 100°C results in anhydrous manganese oxalate.

Ethylene glycol-modified cobalt and iron oxalates as precursors for the synthesis of oxides as extended microsized and nanosized objects

The reactions of ethylene glycol with iron and cobalt oxalates upon heating in air are reported. Heat treatment of mixtures of oxalate powders with ethylene glycol yields new compounds (solvates) via the replacement of the water molecules in the oxalate structure by ethylene glycol molecules: MC2O4 · 2H2O + HOCH2CH2OH = MC2O4(HOCH2CH2OH)+2H2O↑. The crystals resulting from this reaction are elongated, and their shape is inherited by their thermolysis products. Thermolysis in air yields microwhiskers and nanowhiskers of Fe2O3 and Co3O4, and thermolysis in an inert atmosphere affords Fe3O4 and Co whiskers. The thermolysis of FeC2O4(HOCH2CH2OH) in helium yields a new structural modification of FeC2O4 as an intermediate product. The resulting compounds and their thermolysis products were characterized by X-ray powder diffraction, microscopy, IR spectroscopy, and thermogravimetric and chemical analyses. The particle shape and size were determined by scanning electron microscopy.

Synthesis, structure, and magnetic properties of rare-earth-doped Ni0.75Zn0.25Fe2O4 nickel zinc ferrite

We have developed processes for the synthesis of Ni0.75Zn0.25Fe2–xLnxO4 ferrite solid solutions with the spinel structure and investigated the effect of the rare-earth elements Nd, Gd, Yb, and Lu on the chemical composition, extent, lattice parameters, and magnetic properties of the solid solutions. The results demonstrate that rare-earth solubility in the parent spinel reaches ≈2.5 at %, which leads to changes in the magnetic characteristics of the material, in particular in its saturation magnetization Ms, TC, and coercive force Hc.

Synthesis and magnetic properties of a new layered oxide La1.5Sr1.5Mn1.25Ni0.75O6.67

A new oxide phase La1.5Sr1.5 Mn1.25Ni0.75O6.67 ± 0.05, a member of the An + 1 BnO3n+1(n=2) Rad-dlesden—Popper homologue series, was synthesized, and its structure and magnetic properties characterized. Magnetic anomalies associated with the competition between antiferromagnetic and ferromagnetic orders are observed in the range of the temperatures studied (2-400 K). The ESR spectra of the compound feature the constriction of a magnetic signal and a shift toward g(Mn4+).

Magnetic properties of Er2Mn2/3Re4/3O7, a new zirkelite-structure oxide

We have studied the magnetic properties of the new compound Er2Mn2/3Re4/3O7 prepared by reacting Er3ReO8, ReO2, MnO, and metallic Re at 1020°C in silica tubes sealed off under vacuum. The compound is shown to have the zirkelite structure with hexagonal cell parameters a = 7.3174(6) Å and c = 17.365(1) Å (sp. gr. P31211, Z = 6). Magnetization data obtained in the range 2–300 K demonstrate that, above ∼150 K, its magnetic susceptibility exhibits Curie-Weiss behavior with an effective magnetic moment of 9.50μB. Dynamic magnetic susceptibility measurements point to spin-glass behavior of this compound at low temperatures.

Synthesis and magnetic properties of Y0.5Ca0.5BaCo4 − xZnxO7+δ (x = 0, 1.0) solid solutions

We have synthesized Y0.5Ca0.5BaCo4 − xZnxO7 (x = 0, 1.0) solid solutions using solid-state reactions and a glycine-nitrate route and investigated their crystal structure, microstructure, and thermal behavior in an oxygen atmosphere. The effect of Zn on the magnetic behavior of the Y0.5Ca0.5BaCo3ZnO7 cobaltite has been examined.