INTECIN   20395
INSTITUTO DE TECNOLOGIAS Y CIENCIAS DE LA INGENIERIA "HILARIO FERNANDEZ LONG"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
First Order Reversal Curve analysis on NdFeB Nanocomposite Ribbons Treated by Joule Heating
Autor/es:
PAMPILLO, L. G.; SACCONE, F. D.; KNOBEL, M.; SIRKIN, H. R. M.
Lugar:
Gijón
Reunión:
Simposio; International Simposium on Metastable, Amorphous and Nanostructured Materials, ISMANAM 2008; 2011
Institución organizadora:
Universidad de Oviedo
Resumen:
Exchange-spring magnets exhibit interesting properties, such as remanence enhancement, moderated to high coercivities and theoretically expected energy products as higher as 8 GJ/m3 [1]. These properties are due to exchange coupling between a hard and a soft magnetic phases at nanometric scale. Magnetic response is widely dependent on the precipitated phases. In this work, we produced Nd4.5Fe72-xCo3+xCr2Al1B17.5 (x = 0, 2, 7, 12) amorphous ribbons employing the melt-spinning technique. The ribbons were subsequently treated by Joule heating in order to obtain an appropiated nanostructure for goog magnetic performance. We used a variation of this technique, called linearly varying current Joule heating (LVC-JH) [2]. The main characteristic of this method is that the applied electrical current varies slowly up to its final value instead of being rapidly set to a fixed intensity. In this way, it is possible to interrupt the annealing runs in precise points, allowing to determine specific annealing parameters to obtain optimum properties. By means of Mössbauer effect spectroscopy (ME) and X-ray diffraction (XRD) were determined their crystallization kinetic and precipitated phases. We found that those samples with a higher amount of amorphous phase, in coexistence with small nanograins, show enhanced coercive fields. FORC distributions of different samples were analyzed in order to correlate observed interactions and structural modifications. The FORC diagrams revealed that at the first crystallization stage a broad interaction maximum at null field appears, and this is correlated with decoupled phases. For Joule-heated Nd4.5Fe72Co3Cr2Al1B17.5 ribbons at Imax= 0.5 A, we found that dipolar interactions have their maximum at around 3 kOe. Increasing the Imax up to 1.2 A (before the start of a secondary crystallization) this maximum is reduced up to 1 kOe, in coincidence with the corresponding hysteresis cicles that exhibit lower coercive fields and a twist of the main axis due to the reorientation of the ribbons magnetic anisotropy. [1] E. Kneller, R. Hawig, IEEE Trans. Magn. 27, (1991) 3588. [2] F. C. S. da Silva, E. F. Ferrari, M. Knobel, J. Appl. Phys. 84, (1998) 5366.