Fe3O4 Verwey transition. Calorimetric determination of the effects of concentration of Zn and Cd dopants

Abstract

To determine the effect of increase of the lattice constant and decrease in electron concentration on the Verwey transition in Fe3O4, heat capacity measurements have been made on Zn− and Cd−doped Fe3O4 from 5 to 350 K. Bifurcation of the anomaly depends sensitively on the nature and concentration of dopant. Although high dopant levels (e.g., Cd(0.010)) occasion the diminuition of the transitional enthalpy increment, for lower concentration (e.g., Cd(0.005)) the bifurcation has disappeared and both anomalies are merged into a single peak. At even higher dopant levels (e.g., Zn(0.066)) virtually no anomaly is evident over the transition region but an excess heat capacity in the region 25 to 150 K can be discerned. The doping occasions upward migration of the higher‐temperature anomaly and downward migration of the lower‐temperature anomaly. The former is consistent with the prediction of the Wigner crystallization model and the latter with the usual behavior of an order‐disorder transition.