First order reversal curve analysis on NdFeB nanocomposite ribbons subjected to Joule heating treatments
| Autor: | Knobel, Marcelo, 1968 |
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| Přispěvatelé: | UNIVERSIDADE ESTADUAL DE CAMPINAS |
| Rok vydání: | 2012 |
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| Zdroj: | Repositório da Produção Científica e Intelectual da Unicamp Universidade Estadual de Campinas (UNICAMP) instacron:UNICAMP |
| Popis: | Agradecimentos: The authors are grateful to CAPES-SPU cooperation research project "Propriedades magnéticas e de transporte de sistemas nanoestruturados" and Conicet (Argentina) for partial support of this work Abstract: Amorphous precursors with composition Nd4.5Fe72-xCo3+xCr2Al1B17.5 (x = 0, 2, 7, 12) were thermally treated by the Joule heating technique with a linearly varying electrical current. The crystallization kinetics was followed by monitoring the resistance of the ribbons during the heating up to the final applied current. Crystallized nanostructured hases coexist with an amorphous matrix, as it was observed by means of Mossbauer Spectroscopy and X-ray diffraction. The irreversible magnetic response of the Joule heated ribbons was analyzed by the First Order Reversal Curves (FORC) diagram technique. For the optimal treatments, associated with the higher maximum energy products for each sample composition, it was found that the main interaction is of a strongly dipolar characteristic. Over annealed samples show a FORC diagram that gives into account of softening, due to grain growth, for those phases precipitated at the first crystallization stage. When it is measured at 20 K, the hardest magnetic sample (Fe = 72 at.%, Co = 3 at.%, I-final = 0.5 A), exhibits a diagram with characteristics corresponding to dipolar interactions of soft phases. This fact is consistent with an enhancement of the exchange length due to the increase in the soft phase stiffness as it is expected at low temperatures COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Fechado |
| Databáze: | OpenAIRE |
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