J. Rodríguez

Spin glass behaviour in an antiferromagnetic non-frustrated lattice: Sr2FeNbO6 perovskite

From magnetic susceptibility and hysteresis loop measurements on the cubic perovskite Sr2FeNbO6, it is shown that a spin glass transition does exist in this compound which has a non-frustrated lattice, and only antiferromagnetic interactions. This experimental results allows the authors to conclude that lattice frustration is not an essential feature for the spin glass transition in antiferromagnetic insulators. Moreover, it is argued that short-range atomic correlations, which modify the magnetic phase diagrams of the diluted compounds, make this spin glass transition possible.

Structural and magnetic characterization of the lithiated iron oxide LixFe3O4

The Rietveld profile‐analysis method is used to investigate the x‐ray diffraction pattern of lithiated Fe3O4. It is shown that, after exposure to air, pure magnetite coexists with a lithium‐inserted LixFe3O4 phase. The Mossbauer spectra at 300 and 4.2 K have been used to estimate the lithium content of the sample, the pure magnetite concentration, and the iron distribution over the available 16c and 16d sites of the spinel structure. Magnetization measurements from 4.2 to 120 K with an external magnetic field up to 150 kOe have been used to obtain the saturation magnetic moment, the magnetic anisotropy constants, and the susceptibility. It is concluded that a noncollinear spin structure should be present in Li0.5Fe3O4. These results indicate that there is no room‐temperature extrusion of iron even for x→2.0, but that on exposure to air LixFe3O4 samples with x>0.5 are oxidized at room temperature by delithiation.

Magnetic and structural characterization of the solid solution CdFe2O4NiFe2O4

By means of Mossbauer spectroscopy magnetization measurements and powder diagrams, the structural and magnetic properties of the isomorphous series Cd1−xNixFe2O4 has been studied. The cationic distribution depends on the relative concentration of Cd and Ni. The exchange integrals between the two sites in the spinel have been obtained.

Mössbauer emission spectroscopy of doped 57Co1−xO—I. Acceptor impurities: 57Co1−xO:Li

Abstract Mossbauer emission studies on Li-doped 57Co1−xO have been carried out It is shown that the number of Co vacancies as well as the number of L1+ impurities entering the lattice determine the Fe3+ fraction in the emission spectra A recombination model based on the acceptor character of the defects existing in the lattice is proposed This model reproduces well all the Mossbauer data.

Mössbauer emission spectroscopy of doped 57Co1−xO—II. donor impurities: 57Co1−xO:Fe, Ti, In

Abstract Mossbauer emission studies of Fe, In, and Ti doped 57 Co 1− x O have been earned out The appearance of the anomalous ferrice line is due to the existence of cationic vacancies and impurity acceptor levels An electron recombination model is proposed which takes into account the electronic character of the impurity defects.

Mössbauer characterization of LixFe3O4

Mössbauer spectra of lithium intercalated Fe3O4, have been recorded at 300 K and 4.2 K. It has been observed that lithium can be incorporated and/or extruded at room temperature. The coexistence of lithiated and unlithiated particles after exposure of the sample to air, is interpreted in terms of the Li+-ion mobility. The results are compared with those obtained from X-Ray diffraction data and magnetization measurements.