Magnetic and dielectric study of GdFe2O4

Abstract

Mixed iron and rare-earth compounds, particularly mixed oxides, yield wide-ranging physical properties [1, 2]. We have investigated the electrical and magnetic properties of several such materials [3-11]. These and other studies reveal that the coexistence of ordered magnetic behaviour and ferroelectricity is quite a rare occurrence. This letter reports the magnetic and dielectric properties of GdFe20 4. The material was prepared in the laboratory by the usual solid-state reaction technique. The starting materials, Gd203 and Fe203, both with stated purity of 99.99% obtained from Messrs Rarco and Chempure, India, were dried at around 500 K for a few hours before use. The stoichiometric amounts of the starting materials were thoroughly mixed, made into pellets and fired in a platinum crucible in air at around 1500K for 50h with one intermediate grinding. This process has been found to be sufficient for the formation of single-phase GdFe204. The X-ray diffraction (XRD) pattern of the sample was taken using the CuK~ line ()~ = 0.15418 nm). The experimental and calculated values of the Bragg plane separation (dhkl) together with the values of the Miller indices (h k l) and relative intensities of the observed peaks are given in Table I. It was resolved that the material has an orthorhombic unit cell with the cell parameters a 0 = 0 . 6 2 4 2 n m , b0 = 0.7366 nm and Co = 0.8836 nm at room temperature. The density measurement indicates that there must be four formula units per unit cell. The magnetic susceptibility (X) of the powdered sample was measured using the Faraday method [12]. Pellets made at a pelletizing pressure of P > 6 x 108 N m -2 were used for the measurement of the dielectric constant. These pellets were sintered at around 1200K for 50h in air before measurement. The dielectric constant (K'p) of the pellets was evaluated by measuring the capacitance using a V L C R 7 bridge. The magnetic susceptibility of the powdered material prepared in two lots was measured as a function of temperature. The variation of inverse molar magnetic susceptibility (X~ 1) with temperature is shown in Fig. 1. It is seen from this figure that the Xfi 1 versus T plot is not linear. Instead, proceeding from higher to lower temperature there is a systematic trend of points towards the temperature axis. This indicates the onset of short-range magnetic