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This is the accepted manuscript of the following article: Sánchez-Andújar, M., Yáñez-Vilar, S., Biskup, N., Castro-García, S., Mira, J., Rivas, J., & Señarís-Rodríguez, M. (2009). Magnetoelectric behavior in the complex CaMn7O12 perovskite. Journal Of Magnetism And Magnetic Materials, 321(11), 1739-1742. doi: 10.1016/j.jmmm.2009.02.018 We report a magnetoelectric effect in the double perovskite CaMn7O12, that shows a complex magnetic behavior below 90 K with two magnetic phases coexisting (one ferrimagnetic and the other modulated). A second magnetic transition, associated with changes in the magnetic modulation and magnetic ordering coherence lengths of the two magnetic phases occurs at 50 K (TN2). A detailed structural characterization of this compound, that we have carried out by means of high-resolution X-ray powder diffraction, reveals an anisotropic thermal expansion of its lattice parameters at 50 K (TN2). In addition, our study of the complex permittivity of this sample as a function of temperature, frequency and magnetic field shows very interesting results below 90 K and specially below 50 K: the dielectric constant ε′r that was decreasing continuously on cooling experiences an upturn, and even more, on application of a magnetic field it shows a moderate magnetoelectric response. We attribute such dielectric behavior to the formation of electric dipoles by magnetostriction in this charge and spin ordered system, that are sensible to the presence of an external magnetic field The authors are grateful from financial support for MEC (Spain) under project FEDER MAT 2007-66696 and Xunta de Galicia under project PGIDIT06PXB103298PR. S. Yáñez-Vilar want to thank to MEC of Spain for her FPI fellowship and M. Sánchez-Andújar acknowledges to Xunta de Galicia for support under program Parga Pondal SI

We report the synthesis of the Ruddlesden–Popper material Sr 3 Fe 1.5 Co 0.5 O 6.67 (a compound usually obtained under high-pressure conditions) by a simpler normal pressure liquid-mix method and its structural characterization by means of X-ray powder diffraction. In this material—which is semiconducting and shows a glassy magnetic behavior—the combination of the reduced dimensionality of the structure compared to 3D perovskites, the small grain size obtained by our synthesis method and the selected stoichiometry, results in a record magnetoresistance in these kind of compounds, −47% at T =5 K and H =50 kOe, that is explained on the basis of intragranular and intergranular effects.

Measurements of the temperature dependence of the magnetization (and parameters like coercivity and susceptibility) of La1-xSrxCoO3 (0.20 ≤ x ≤ 0.30) perovskites are presented. Particular attention is given to the interval of temperatures containing the ferro-paramagnetic phase transition. Curie temperature values lower than those reported previously and critical exponents are given. Additionally, the coercivity as well as the parameters of the law of approach to magnetic saturation are experimentally determined. Anomalies in Curie temperature, coercivity and law of approach to saturation are introduced confirming a non-conventional transition from ferromagnetic to paramagnetic states. © 1999 Elsevier Science B.V. All rights reserved.

In this work we report magnetically modulated microwave absorption experiments performed at 9.4 GHz from 110 up to 300 K on samples of Pr 1−x Ba x CoO 3−δ (0.10 which were prepared by the “Pechini” method.

We have studied the AC and DC magnetic properties of the lamellar compounds La 1− x Sr 1+ x CoO 4 (0⩽ x ⩽0.4). These materials are found to evolve towards an anomalous “cluster-glass”-like behaviour as x increases. The onset of the ferromagnetic order in the bidimensional phases is seen to occur at around 150 K, followed by a blocking process around 125 K. Also, present in the magnetic behaviour of these materials is the signal coming from small intergrowths of a perovskite phase, also detected by TEM, although invisible for powder-X-ray diffraction.

We have prepared polycrystalline La 1- x Sr x CoO 3 (0 x ⩽ 0.50) particles using the ceramic method and other alternative soft-chemistry techniques that yield materials with smaller particle size. The study of their magnetic and electrical properties shows differences between these series of samples, among them: changes in the compositional range for ferromagnetic behaviour, magnetic hardening as the particles get smaller; different composition for the metal-insulator transition, and changes in the conduction regime in the semiconducting interval. We try to interpret these differences taking into account the inhomogeneous electronic structure of these doped cobaltates.