DYNAMIC BEHAVIOR OF THERMOMAGNETIC GAS TORQUE

The recently discovered thermomagnetic gas torque shows twofold behavior in the presence of a large modulating magnetic field collinear with the steady magnetic field. At steady fields of about one-half H0 (the field for maximum torque), the torque N is decreased by an amount ΔN if the modulation frequency ν is low compared to a collision frequency. As ν is increased, the torque returns to the value it had in the absence of modulation. From plots of ΔN versus ν, we have determined correlation frequencies νc for the collision processes. We find that, for high-enough pressure P, νc varies linearly with P for NO, O2, N2, and HD gases. However, it appears that although elastic collisions are the controlling process in the gas torque for NO, O2, and N2, inelastic collisions determine the gas-torque behavior for HD (at least for the low-field torque peak). At steady fields greater than 2H0, a precession-related phenomenon shows up as dispersionlike curves in plots of ΔN versus ν. For NO, such curves are observable at the molecular magnetic Larmor frequency and twice the Larmor frequency. From double-frequency curves, we obtain gJ=-49.3μN, in good agreement with Ramsey's value of -48.2. Although the dispersion curves cannot be resolved, precession-related phenomena are observable for O2, and HD. We can estimate that the gJ values effective in the gas-torque phenomena are ∼ -10 and +1 μN for O2 and HD. The value for O2 agrees quite well with the average expected for Ms=0 molecules in fast rotational states (K9). The value for HD is in order-of-magnitude agreement with measurements of Ramsey. © 1969 The American Physical Society.