Critical behaviour of thermal resistivity of Ni

Abstract

Accurate data are presented on the behaviour of the thermal conductivity K as a function of temperature for a pure Ni sample near its Curie point. Previous results on the electrical resistivity (Q, dQ/dT) are used to explain the temperature-dependence of K(T). The results are analysed in terms of electron-phonon and s-d exchange interactions. The critical behaviour of the thermal resistivity W(= K-~) has also been investigated.Study of the transport properties of magnetic phase transitions provides a sensitive and often rather simple means of investigation details of the microscopic interactions. The electrical resistivity Q in particular has received a good deal of attention [1][2][3][4][5][6][7]. The scanty experimental information available on the thermal conductivity K of magnetic materials and on the complex behaviour which occurs in the transition region earlier precluded any discussion on such matters as the values of the critical exponents. Accordingly, only general features were considered [8][9][10][11][12]. The critical exponents are of interest because many different kinds of physical systems behave in a similar way near the critical point To. This work reports for the first time the critical exponents of the thermal resistivity of pure Ni both below and above To. The universality concept [4,5,13] is also tested.In ferromagnetic metals and alloys, the most characteristic interaction is the s-d interaction, i.e. the spin exchange interaction between the conduction (s) and unfilled shell (d) electrons. According to Kasuya [1], this exchange interaction depends on the relative orientation of the spins of both electrons. Therefore, at T= 0all the spins of d-electrons being in order, there is no electrical resistance, while at a finite temperature this order is disturbed and thus a resistance appears and increases with temperature. Above To, the directions of the d-electron spins become perfectly random, and the electrical resistance remains constant. The resistivity caused by such a process is called the spin-fluctuation [3] or spin-disorder contribution [10].