New magnetic materials for high performance magnets

Author(s)

Regina Keiko Murakami

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2005-09-19

Examining board members

Hercilio Rodolfo Rechenberg; Vitoria Maria Tupinambá Souza Barthem; Rubens Nunes de Faria Junior; Frank Patrick Missell; Augusto Camara Neiva

• Advisor: Hercilio Rodolfo Rechenberg; Valquiria Villas Boas Gomes Missell

Abstract

The aim of the present work was to develop new improved magnetic materials suitable for permanent magnets. Two kinds of materials were studied: (Nd,Sm)5(Fe,MT)17 based materials, were MT is a transition metal and, (Nd,Pr)FeB nanocrystalline materials (exchange spring magnets) with TiC additions. The 5:17 alloys were melted in an arc melting furnace followed by a long annealing (at least 30 days). We tried to improve the magnetic properties by means of chemical substitutions (Ti, Co, Mn, etc.) and/or by addition of interstitial atoms of deuterium or nitrogen. The samples were characterized by means of thermomagnetic analysis (TMA), low temperature magnetometry, X ray and neutron diffraction, and Mössbauer spectroscopy. The main results were: a) increase of Tc temperature (up to 70 ºC) and; b) determination of interstitial sites for deuterium. (Nd,Pr)FeB alloys with TiC additions were melted in an arc melting furnace, being processed in a melt spinner system. After the samples were heat treated at different temperatures. The promissing literature results for Nd2Fe14B+TiC were also obtained for Pr2Fe14B + TiC, but not for systems composed by Pr2Fe14B and Fe3B phases with TiC additions. However, good results were obtained in systems composed by Pr2Fe14B and α-Fe with TiC additions, with 30% increase on coercive field values Hc, and 15% increase on (BH)max. (AU)