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A series of the flake-like and sphere-like nanocrystalline carbonyl-iron powders (CIPs) were prepared by high energy ball milling raw CIPs for different times (t). Variations of the structure, morphology, microwave complex permeability, and static magnetization with t for the two kinds of CIPs have been investigated using x-ray diffraction, scanning electron microscopy, vector network analyzer, and vibrating sample magnetometer, respectively. The results show that with prolonging t, the nature resonance frequency (fr) and internal strain (〈ɛ〉) increase monotonously for the sphere-like nanocrystalline CIPs, while those fluctuate for the flake-like nanocrystalline CIPs. These phenomena are in accordance with the increasing fr with increasing 〈ɛ〉, suggesting that 〈ɛ〉 suppresses the domain wall displacement and promotes the gyromagnetic spin rotation. As a result, the competition between the domain wall displacement and the gyromagnetic spin rotation can be effectively controlled by 〈ɛ〉 in the as-milled nanoc...

Microstructural studies show that manganites La1−xBaxMnO3 (0.33≤x≤0.95) begin structural phase separation into La0.67Ba0.33MnO3 and BaMnO3 for x>0.33. These composites form a cellularlike structure when the volume faction of La0.67Ba0.33MnO3 (fLBMO) is near the percolation threshold (fC). The percolation threshold (fC) for our composites is 0.18. This result is not consistent with the previous results, which prefer smaller percolation threshold value. This could be attributed to the contribution of grain boundaries. This grain-boundary contribution also induces the large low-temperature bump in electrical transport. The critical exponents t gained from the good fitting for the experimental data are 1.6 at 150 K and 1.7 at 300 K, which are in good agreement with the previous universal result: t=1.6–2.0 for the three dimensional space.

A series of Ni(1−x)FexO (x=0, 0.015, 0.03, 0.05, and 0.1) bulk samples was synthesized by the chemical concentration-precipitation method. Phase composition analysis was carried out, which showed that trace amounts of ferromagnetic phase NiFe2O4 could not be detected by x-ray diffraction in these bulk samples with x≤0.03. When x>0.03, NiFe2O4 ferrite is detected easily. The magnetic properties of all the bulk samples were investigated by measuring their magnetization as a function of temperature and magnetic field. The results indicated that all the bulk samples sintered in air exhibited large room-temperature ferromagnetic behavior ascribed to a ferromagnetic impurity phase. Simultaneously, an exchange bias and training effect were also observed in all the bulk samples, suggesting the possibility of the existence of a strong ferromagnetic/antiferromagnetic exchange coupling in this kind of compound. Specifically, the exchange bias field could be tuned by changing the concentration of the Fe dopant.