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Using a sol-gel method we have prepared monodispersive particles of La0.67Ca0.33MnO3 in the range from 20 to 110 nm at temperatures from 540 to 1000 °C. A magnetoresistance above 10% was obtained in a field of 1 kOe for all the particles sizes. These results may be relevant for future applications.

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A Raman spectroscopic study of the high-frequency optical phonons in single crystals of the multiferroic system RMn 2 O 5 ͑R = Bi, Eu, Dy͒ was performed. All studied materials show anomalous phonon shifts, below a new characteristic temperature for these materials, T * ϳ 60-65 K. The sign and magnitude of such shifts appear to be correlated with the ionic radius of R, envolving from softenings for R = Bi to hardenings for R = Dy and showing an intermediary behavior for R = Eu. Additional phonon anomalies were identified below ϳT N ϳ 40-43 K, reflecting the onset of long-range ferroelectric and/or magnetic order of the Mn sublattice. Complementary dc-magnetic susceptibility ͓͑T͔͒ measurements for BiMn 2 O 5 up to 800 K yield a Curie-Weiss temperature CW = −253͑3͒ K, revealing a fairly large frustration ratio ͉͑ CW ͉ / T N = 6.3͒. Deviations of ͑T͒ from a Curie-Weiss paramagnetic behavior due to magnetic correlations were observed below temperatures of the order of ͉ CW ͉, with the inverse susceptibility showing inflection points at ϳ160 K and ϳT *. Supported by ͑T͒ data, the anomalous Raman phonon shifts below T * are interpreted in terms of the spinphonon coupling, in a scenario of strong magnetic correlations. Overall, these results support significant magnetic frustration, introduce a new characteristic temperature ͑T * ͒, and suggest a surprisingly rich behavior for the magnetic correlations in the paramagnetic phase of this system.

Neutron-diffraction measurements in LaCrSb3 show a coexistence of ferromagnetic and antiferromagnetic sublattices below T(C)=126 K, with ordered moments of 1.65(4) and 0.49(4)mu(B)/formula unit, respectively (T=10 K), and a spin-reorientation transition at approximately 95 K. No clear peak or step was observed in the specific heat at T(C). Coexisting localized and itinerant spins are suggested.