Properties of the ferrimagnetic double-perovskite A_{2}FeReO_{6} (A=Ba and Ca)

TL;DR

This study investigates the structural, electrical, and magnetic properties of double-perovskite ceramics A_{2}FeReO_{6} (A=Ba, Ca), revealing their distinct metallic or semiconducting behavior and ferrimagnetism with high Curie temperatures.

Contribution

It provides detailed characterization of Ba_{2}FeReO_{6} and Ca_{2}FeReO_{6}, including their structures, magnetic transition temperatures, and electronic properties, highlighting differences due to A-site cation substitution.

Findings

Ba_{2}FeReO_{6} is cubic and metallic from 5 K to 385 K.

Ca_{2}FeReO_{6} is monoclinic and semiconducting over the same temperature range.

Ba_{2}FeReO_{6} exhibits negative magnetoresistance of 10% at 5 K in a 5 T field.

Abstract

Ceramics of A_{2}FeReO_{6} double-perovskite have been prepared and studied for A=Ba and Ca. Ba_{2}FeReO_{6} has a cubic structure (Fm3m) with $a\approx $8.0854(1) \AA whereas Ca_{2}FeReO_{6} has a distorted monoclinic symmetry with $a\approx 5.396(1) \AA, b\approx 5.522(1) \AA, c\approx 7.688(2) \AA$ and $\beta =90.4^{\circ} (P21/n)$. The barium compound is metallic from 5 K to 385 K, i.e. no metal-insulator transition has been seen up to 385 K, and the calcium compound is semiconducting from 5 K to 385 K. Magnetization measurements show a ferrimagnetic behavior for both materials, with T_{c}=315 K for Ba_{2}FeReO_{6} and above 385 K for Ca_{2}FeReO_{6}. A specific heat measurement on the barium compound gave an electron density of states at the Fermi level, N(E_{F}) equal to 6.1$\times 10^{24} eV^{-1}mole^{-1}$. At 5 K, we observed a negative magnetoresistance of 10 % in a magnetic field of 5 T, but only for Ba_{2}FeReO_{6}. Electrical, thermal and magnetic properties are discussed and compared to the analogous compounds Sr_{2}Fe(Mo,Re)O_{6}.