磁熵变化值是衡鼋磁制冷材料好坏的一项重要指标.基于前差商的数值方法,利用温度插值方法分别计算了球体材料和长径比为5的长圆柱体材料的在低场下(＜2 T)扣除退磁场后的实际磁熵变,研究了由材料形状引起的退磁效应对磁制冷材料磁熵变的影响.结果表明,长圆柱体材料的实际磁熵变最接近无退磁场情况下的理论值,而球体材料退磁场很大,其实际磁熵变大大低于理论值;随外场的增强,退磁场对磁熵变的影响逐渐减弱;另外随温度升高退磁场所带来的影响逐渐减弱;若材料本身的磁熵变数值较大,则退磁场的影响相对较小.
The magnetic entropy changes were the benchmark for the application of the magnetocaloric materials.In this paper,the net entropy changes under low magnetic fields(＜2 T),values eliminating the influence of demagnetizing effect of spherical materials and cylindrical materials with the length-diameter of 5 were calculated by using the temperature interpolation method,which was based on the forward difference quotient principle.Results indicated that the net entropy changes of materials with the cylindrical shape were close to the theoretical ones if there was no demagnetizing effect,while the net entropy changes of spherical materials were remarkably smaller than the theoretical ones.It was ascribing to the strong demagnetizing field inside the materials.In addition,such influence of demagnetizing effect was weakened with beth the increase of magnetic field and temperature.If the entropy changes of the materials were larger,the influence of demagnetizing effect was relatively small.
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