如何确定居里温度

Measuring the Curie temperature

居里温度是磁性矿物的特征温度,通常我们利用实验室测量的居里温度(T_c)来鉴别岩石中的磁性矿物种类.由于磁性矿物的粒径以及其他金属的取代等都会对T_c产生影响,因而准确确定T_c对于判断磁性矿物的粒径分布和其他金属的取代程度等具有重要的意义.目前实验室中主要通过测量热磁曲线获取矿物的居里温度,包括磁化强度随温度的变化曲线(M_sT曲线)和磁化率随温度的变化曲线(χ-T曲线)两种传统测量方法.对于M_s-T曲线,通常确定T_c的方法有图解法,求导法和外推法(extrapolation);而对于χ-T曲线,确定T_c的方法除了图解法,求导法之外,还主要包括Hopkinson峰值法、1/χ法.近期随着仪器的更新,可以测量不同温度下1/4段磁滞回线,该方法不仅可获得传统的M_s-T和χ-T曲线,还可以获得不同磁场强度下磁化强度随温度的变化曲线以及高场磁化率随温度(χ_h-T)的变化曲线和Arrott图(磁化强度的立方M^3与磁场h的相关性图),进而获取多种参数来计算T_c,是确定T_c的一种新的方法.本文简要综述了这些方法的原理及应用实例.

The curie temperature（Tc） is the characteristic of magnetic minerals. It is useful to determine magnetic mineralogy.Correct determination of the Curie point is also important for investigating the grain size distribution and the degree of substitution of magnetic minerals due to the great effect of these characteristics on Tc. Thermomagnetic analyses are the main way in lab to determine Tc. High-temperature magnetization（Ms-T） and magnetic initial susceptibility（χ-T） curves are common evaluation routines of Tc. There are several analytical methods to determine Tc on Ms-T curves,such as the two-tangent method,the derivative method and extrapolation approach. For χ-T curves, the determination ways include Hopkinson peak method and 1/χmethod,except the two-tangent method and the derivative method.Recently, as the development of magnetic instrument, a new procedure is proposed to determine Tcby measuring quarterhysteresis loops during a single heating cycle. Except traditional Ms-T and χ-T curves,M-T curves under different external magnetic field,χ-T curve under high magnetic field（χh-T） and ＂Arrott ＂plot（the correlation plot of cubic magnetization（M^3） and magnetic field（h）） can be obtained in this method. More data available in this measurement can correctly determine Tc. This paper will summarize these methods for determining Tc.