In this work the physical properties of the intermetallic compound TbRhIn 5 were investigated by means of temperature-dependent magnetic susceptibility, electrical resistivity, heat-capacity, and resonant x-ray magnetic diffraction experiments. TbRhIn 5 is an intermetallic compound that orders antiferromagnetically at T N = 45.5 K, the highest ordering temperature among the existing RRhIn 5 ͑1-1-5, R = rare earth͒ materials, which in contrast to what is expected from a de Gennes scaling along the RRhIn 5 series. The x-ray resonant diffraction data have allowed us to solve the magnetic structure of TbRhIn 5 . Below T N , we found a commensurate antiferromagnetic structure with a propagation vector ͑1/2,0,1/2͒ and the Tb moments oriented along the c axis. Strong ͑over two orders of magnitude͒ dipolar enhancements of the magnetic Bragg peaks were observed at both Tb absorption edges L II and L III , indicating a fairly high polarization of the Tb 5d levels. Using a mean-field model including an isotropic first-neighbor exchange interaction ͑J R-R ͒ and the tetragonal crystalline electrical field ͑CEF͒, we evaluate the influence of the CEF effects in the physical properties of TbRhIn 5 . The results reported here seem to corroborate a general trend of CEF-driven effects on T N along the RRhIn 5 series.

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We report experiments of electron spin resonance ͑ESR͒ of Cu 2+ in polycrystalline samples of CaCu 3 Ti 4 O 12 post-annealed in different atmospheres. After being synthesized by solid state reaction, pellets of CaCu 3 Ti 4 O 12 were annealed for 24 h at 1000°C under air, Ar or O 2 . Our temperature dependent ESR data revealed for all samples nearly temperature independent g value ͑2.15͑1͒͒ and linewidth for T ӷ T N Ϸ 25 K. However, the values of ESR linewidth are strongly affected by the oxygen content in the sample. For instance, argon post-annealed samples show a much larger linewidth than the O 2 or air post-annealed samples. We attribute this broadening to an increase of the dipolar homogeneous broadening of the Cu 2+ ESR lines due to the presence of oxygen vacancies which induce an S =1/2 spin inside the TiO 6 octahedra. Correlation between a systematic dependence of the ESR linewidth on the oxygen content and the high dielectric constant of these materials is addressed. Also, ESR, magnetic susceptibility, and specific heat data for a single crystal of CaCu 3 Ti 4 O 12 and for polycrystals of CdCu 3 Ti 4 O 12 are reported.

We have synthesized single crystalline samples of Gd3Co4Sn13 intermetallic compound using a Sn-flux method. This compound crystallizes with a cubic Yb3Co4Sn13-type structure, space group Pm-3n, which has 40 atoms per unit cell. Measurements of the magnetic susceptibility, heat capacity, electrical resistivity, and electron spin resonance (ESR) revealed that Gd3Co4Sn13 is a metallic Curie-Weiss paramagnet at high temperature and presents an antiferromagnetic ordering below TN=14.5K. In the paramagnetic state, a single Gd3+ ESR line with a nearly temperature independent g∼2.005(2) is observed, and its linewidth follows a Korringa-like behavior as a function of temperature. From the Korringa rate (ΔH∕ΔT∼4Oe∕K) and g-shift (Δg∼0.012) obtained from the ESR experiments combined with the magnetic susceptibility and specific heat data for Gd3Co4Sn13, we have extracted the exchange parameters between the Gd3+ local moments and the conduction-electrons (c-e) in this compound. This exchange parameter Jfs≈10meV was found to be c-e wave-vector independent and the electronic structure of Gd3Co4Sn13 has a single band character.

In this work we have synthesized polycrystalline samples for the series of double-perovskite Ca2−xLaxFeIrO6. Their structural and magnetic properties were investigated using experiments of magnetic susceptibility and x-ray powder diffraction. The Ca2−xLaxFeIrO6 compounds form in a monoclinic structure, space group P21∕n, with the presence of significant Fe∕Ir cationic disorder. Interestingly, our results indicate a change in the nature of the microscopic magnetic interaction induced by La doping, where the system seems to evolve from antiferromagnetic in the extremities of the series, x=0 (TN≈75K) and x=2.0, to ferrimagnetic in intermediate regions of the series. However, due to significant presence of disorder and strong competition between ferromagnetic and antiferromagnetic interactions, the saturation of the magnetization was not found to be larger than 0.1μB∕Fe.