The Field-Dependent Magnetic Viscosity of FeNdB Permanent Magnets

Abstract

The time-dependent decrease of the magnetic polarization of magnet materials in the presence of an opposing field is well known as the magnetic viscosity or magnetic aftereffect. In previous studies, magnetic viscosity was usually measured in fields when in the vicinity of coercivity (Formula presented.), and this was conducted in order to understand the coercivity mechanism in magnetic materials. In this study, the magnetic viscosity of commercial FeNdB magnets is determined at opposing fields weaker than (Formula presented.) and at different temperatures in the range from 303 to 433 K (i.e., from 30 to 160 °C) by means of a vibrating sample magnetometer (VSM). As a result, the parameter (Formula presented.), which describes the magnetic viscosity in the material, was found to increase with increases in the opposing field. Furthermore, both the parameter (Formula presented.) and its dependence on the temperature were found to correlate with the coercivity (Formula presented.) of the material. Also, a difference with regard to the parameter (Formula presented.) for the materials measured in this study with similar magnetic properties, but which had undergone different types of processing, could not be found. Knowledge of the field- and temperature-dependent behavior of the magnetic viscosity of FeNdB magnets allows for better estimations over the lifetime of a component under operating conditions with respect to the magnetic losses in FeNdB magnets that are used in electric components.