Magnetic Susceptibility of Tetraamminelithium(Zero) in the Range 1.5–194°K

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Abstract
The magnetic susceptibility of the compound tetraamminelithium (zero), Li(NH3)4, has been measured by the Faraday method from 1.5 to 194°K. In the liquid the susceptibility is paramagnetic and shows a small positive temperature coefficient that can be attributed to variation of bandwidth with temperature. At the freezing point, 88.8°K, the susceptibility undergoes a 6% decrease, also attributable to a change in bandwidth. At 82.2°K, where there is a change from cubic to hexagonal structure, the susceptibility shows an abrupt 25% drop and Curie‐Weiss behavior down to about 15°K. Below 15°K, the susceptibility flattens out. Two models are presented to account for the observed behavior. In one, Li(NH3)4 is considered to be an antiferromagnetic metal with a Néel temperature of about 10°K; in the other, a nearly degenerate electron gas. Hysteresis at the 88.8°K and 82.2°K phase transitions has also been investigated. Fermi‐surface topologies for the cubic and hexagonal phases are discussed on the basis of the magnetic susceptibility measurements and existing x‐ray and optical data. The magnetic susceptibilities of pure lithium and pure ammonia have also been measured from 1.5 to 296°K. The lithium susceptibility is small, paramagnetic, and temperature independent both above and below the martensitic transformation. The ammonia susceptibility, which is negative, shows, in absolute value, a small decrease at the freezing point and a temperature‐dependent increase below 20°K.