Electrical transport in gadolinium iron garnet (GdIG)

Abstract

Thermoelectric power [Formula: see text] and electrical conductivity (σ) of Gd3Fe5O12 (gadolinium iron garnet GdIG) have been reported in the temperature range 500 to 1200 K. [Formula: see text] remains almost constant between 600 and 1100 K but it increases with decrease of temperature in accordance with the relation[Formula: see text]Conductivity changes by a factor of five near the ferrimagnetic Curie temperature (Te = 564 K). The log σ vs. T−1 curve also has a break at 900 K. Besides this jump and break the log σ vs. T−1 plot is linear and slopes of these lines correspond to activation energies of 0.55 eV for T < 560 K, 0.75 eV for the temperature range 575–900 K, and 0.92 eV between 900 and 1200 K. It has been concluded that electric conduction up to 1200 K in this compound is extrinsic. Between 575 and 1200 K it is due to hopping of holes from Fe4+ to Fe3+ sites and below 560 K it is due to the band conduction of holes in the valence (O2−, 2p) band.