Temperature Dependence of the Scott Thermomagnetic Torque inN2, CH4, and HD

Abstract

The temperature dependence of the Scott thermomagnetic torque has been measured in ${\mathrm{N}}_2$, C${\mathrm{H}}_4$, and HD. Measurements were made from a temperature of 75 up to 300 °K, from a presure of 0.003 up to 1 Torr, and from a magnetic field of a few oersted up to 440 Oe. In both ${\mathrm{N}}_2$ and C${\mathrm{H}}_4$, the maximum torque measured at each temperature was found to increase when the temperature was increased from 75 to 300 °K. In HD this maximum torque increased when the temperature was increased from 75 up to about 170 °K but then decreased as the temperature was increased further up to 300 °K. When the pressure is large enough, the Scott torque multiplied by the pressure plotted as a function of $\frac{H}{P}$ reaches a limiting curve which has a maximum value at a field-to-pressure ratio ${\left(\frac{H}{P}\right)}_{max}$. The temperature dependence of ${\left(\frac{H}{P}\right)}_{max}$ for ${\mathrm{N}}_2$ and C${\mathrm{H}}_4$ has been measured, and from these data the value for the optimum ratio of precession frequency to collision frequency ${\left(\frac{{\nu }_L}{{\nu }_c}\right)}_{\mathrm{opt}}$ determined. The value of ${\left(\frac{{\nu }_L}{{\nu }_c}\right)}_{\mathrm{opt}}$ for ${\mathrm{N}}_2$ was found to be 0.113 and for C${\mathrm{H}}_4$ 0.128. This means a precession of the rotational magnetic moment about the field axis of only $\frac{1}{8}$ of a revolution between two collisions. There is no adequate theory with which we have been able to fit these temperature-dependent data of the Scott thermomagnetic torque.