Spin Paramagnetism of ${\mathrm{Cr}}^{+++}$, ${\mathrm{Fe}}^{+++}$, and ${\mathrm{Gd}}^{+++}$ at Liquid Helium Temperatures and in Strong Magnetic Fields

A quantitative experimental study of space quantization of magnetic dipoles and quenching of orbital angular momentum has been made by measuring the fractional variation of the magnetic moment of paramagnetic ions with magnetic field strength at fixed temperatures. The study of trivalent chromium ion (${}_{}{}^4{}_{}{}^{}F_{\frac{3}{2}}^{}{}_{}{}^{}$ state for free ion) in potassium chromium alum up to 99.5 percent saturation at 1.29°K and in a field of 50,000 gauss gave a close confirmation of space quantization of magnetic dipoles through compatibility of experimental results with the Brillouin function and very marked incompatibility with the Langevin function. The quenching of orbital angular momentum by the crystalline electric field was demonstrated by the agreement of experimental measurements with a Brillouin function for $g=2\mathrm{}(L=0\mathrm{})\mathrm{}$ as against $g=\frac{2}{5}\mathrm{}(L=5\mathrm{})\mathrm{}$. The paramagnetic saturation of iron (${}_{}{}^6{}_{}{}^{}S_{\frac{5}{2}}^{}{}_{}{}^{}$ for free ion) ammonium alum and gadolinium (${}_{}{}^8{}_{}{}^{}S_{\frac{7}{2}}^{}{}_{}{}^{}$ for free ion) sulfate octahydrate was achieved, thus permitting of speculation as to a small contribution of the crystalline field to the magnetic moment. Some preliminary calculations were made of this effect for iron ammonium alum and compared with experiment. Experimental study of moments consisted in moving a spherical sample with respect to a double coil system and measuring the flux change ballistically. Magnetic moments were reproducible to ∼0.2 percent in mid-range and the magnitude of $\frac{H}{T}$ is known to ∼1.5 percent.