The relationship of thermal expansion to magnetocrystalline anisotropy, spontaneous magnetization, and Tc for permanent magnets

The materials studied here include SmCo5, GdCo5, Sm2TM17, Gd2TM17, Nd9.4Pr4.6Fe80B6, Alnico, SrFe12O19, and PtCo (TM=transition metal). For the first time, the thermal expansion data α(⊥) and α(∥) for the eight materials from as low as −180 °C to as high as 1250 °C have been reported. α(⊥) is the th...

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Bibliographic Details
Published in:Journal of applied physics 1999-04, Vol.85 (8), p.5669-5671
Main Authors: Chen, Christina H., Walmer, Marlin S., Walmer, Michael H., Gong, Wei, Ma, Bao-Min
Format: Article
Language:English
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Summary:The materials studied here include SmCo5, GdCo5, Sm2TM17, Gd2TM17, Nd9.4Pr4.6Fe80B6, Alnico, SrFe12O19, and PtCo (TM=transition metal). For the first time, the thermal expansion data α(⊥) and α(∥) for the eight materials from as low as −180 °C to as high as 1250 °C have been reported. α(⊥) is the thermal expansion coefficient in the base plane and α(∥) is the coefficient in the c axis. All anisotropic materials tested show thermal expansion anisotropy (TEA). The degree of TEA is defined as γ=α(⊥)/α(∥). The γ has been observed to be related to the degree of magnetocrystalline anisotropy field HA. SmCo5 has the highest HA (350 kOe) and the highest γ (2.5). All the materials show thermal anomaly with a changing slope for α(∥) near Tc and near phase transformation temperatures. The magnitude of thermal anomaly has been observed to be related to the magnitude of spontaneous magnetization (SMZ). The most distinct thermal anomalies are observed for Nd9.4Pr4.6Fe80B6, in which both α(⊥) and α(∥) show a deep valley near Tc, and a peak at around the spin-tilt temperature. Nd–Fe–B type material has the highest SMZ and the largest thermal anomaly of all the permanent magnets. Spontaneous magnetostriction occurs mainly in the c axis for RE–Co alloys (RE=rare earth), and in all directions for Nd–Fe–B type alloys. A rubber band model is used to describe the spontaneous magnetostriction force.
ISSN:0021-8979
1089-7550
DOI:10.1063/1.369835