It has been recently reported that some non-magnetic materials in bulk state, exhibit magnetic behavior at the nanscale due to surface and size effects. The experimental observation of these effects is based on the measurement of very small magnetic signals. Thus, some spurious effects that are not critical for bulk materials with large magnetic signals may become important when measuring small signals (typically below 0.0001 emu). Here, we summarize some sources of these small magnetic signals that should be considered when studying this new nanomagnetismComment: 16 pages, 10 figure

The full rare-earth (RE) chromites series (RE)CrO(3) with an orthorhombic distorted (Pnma) perovskite structure and the isostructural compound YCrO(3) can be synthesized through a simple microwave-assisted technique, yielding high-quality materials. Magnetization measurements evidence that the Néel temperature for antiferromagnetic Cr(3+)-Cr(3+) ordering strongly depends on the RE(3+) ionic radius (IOR), and a rich variety of different magnetic spin interactions exists. Dielectric spectroscopy on sintered pellets indicates electronic inhomogeneity in all samples as manifested by the presence of at least two dielectric relaxation processes associated with grain boundary and grain interior bulk contributions. X-ray diffraction, Raman spectroscopy, and temperature-dependent dielectric permittivity data do not indicate potential noncentrosymmetry in the crystal or concomitant ferroelectricity. Strong correlations between the magnetic and dielectric properties were not encountered, and microwave-synthesized (RE)CrO(3) may not be classified as magnetoelectric or multiferroic materials.

The structure of (Li,Na,K)(Nb,Ta,Sb)O 3 piezoelectric ceramics was thoroughly studied by X-ray diffraction (XRD) and Raman spectroscopy for samples with different compositions and sintered for different times. A linear relationship is evidenced between the tetragonality ratio derived from XRD and the Raman shift. The Raman stretching modes are used to demonstrate the correlation of the structure and the piezoelectric properties of the materials, and to calculate the effective ionic displacement causing the piezoelectric polarization. The methodology proposed here offers invaluable insight into the nondestructive Raman analysis of perovskite structures based on the potassium sodium niobate systems, which are not amenable by studies of diffraction or other spectroscopic techniques.

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We report on the magnetic properties of Fe 1−x Al x alloys ͑0.2ഛ x ഛ 0.4͒ produced by mechanical alloying by milling pure element powders for t = 12, 24, and 36 h. The alloys present a bcc lattice with compositional disorder and are ferromagnetic at room temperature, independently of the milling time. The lattice parameter of the x = 0.2 sample presents a small decrease with t, whereas those of the x = 0.3 and 0.4 samples remain constant independently of the milling time. The magnetic properties of the alloys with x = 0.2 and 0.3 do not show important variations with t, while those of x = 0.4 are strongly dependent on the milling time. For this latter alloy it was found that: ͑i͒ despite being the most diluted of the series, it presents a well developed ferromagnetic order at room temperature as the Mössbauer and hysteretic data have shown; ͑ii͒ the temperature dependence of the ac susceptibility and the Mössbauer spectra recorded at different temperatures evidence the occurrence of reentrant spin-glass and superparamagnetic phenomena. The enhancement of the ferromagnetic behavior and the presence of reentrant spin-glass freezing temperature and of a superparamagnetic blocking process are interpreted in terms of a simple localized model based on the disorder present in that alloy and on the occurrence of competitive interactions, namely, the ferromagnetic nearest-neighbor Fe-Fe interactions and the antiferromagnetic near-nearest-neighbor Fe-Fe ones. Taken together, these results evidence that the stabilization of the magnetic order takes place in the x = 0.4 sample exclusively through the induction of compositional disorder and without any contribution from the lattice expansion.