The magnetic susceptibilities of platinum, rhodium and palladium from 20 to 290° K

Abstract

An apparatus is described which makes possible the rapid determination of the temperature variation of the magnetic susceptibilities of small solid specimens. The deflexions of a beam of light passing through a Sucksmith balance are recorded photographically. The temperature of the specimen, measured by a Au-Co/Ag-Au thermocouple in contact with it, is initially reduced to 20° K and deflexions are recorded at small intervals of temperature as the temperature of the specimen rises to 290° K. The whole temperature range can be covered in 4 h. The mean deviation of single measurements from the best smooth curve passing through them is less than 0.2 % of the mass susceptibility of the specimens. The apparatus has been used to measure the temperature variation of the susceptibilities of spectrographically standardized specimens of platinum, rhodium and palladium. Measure­ments on three pure palladium specimens show a maximum in the susceptibility temperature curve at 80° K. The experimental results for platinum show a change in the curvature of the susceptibility temperature curve below 90° K, the susceptibility increasing more rapidly as the temperature decreases. The experimental results for rhodium show a regular increase of susceptibility with increase of temperature. The results for palladium are discussed in relation to the collective electron treatment of metals, and assuming a parabolic distribution of energy states in the d band, estimates are made of the effective Fermi-Dirac degeneracy temperature θ F , the number of holes per atom, q , and the exchange interaction energy θ' . The estimated values are θ F = 1020° K, q = 0.29, θ' = 554.0° K. Similar estimates are made in the case of platinum, the values being θ F =1750° K, q = 0.25, θ' = 770° K.