Structures and Physical Properties of n = 3 Ruddlesden–Popper Compounds Ca4Mn3−xNbxO10 (0 ≤ x ≤ 0.2)

Abstract

The Ruddlesden–Popper series of compounds Ca4Mn3−xNbxO10 (x = 0–0.2) have been prepared by solid-state methods. Structural, magnetic, electrical, and magnetoresistive studies were performed on the compounds. Nb doping caused increases in both unit cell volume and octahedral distortion. The magnetization measurements indicated that the doped samples displayed ferromagnetism-like behavior, which could be explained by the double-exchange interaction between Mn4+ and Mn3+ induced by the charge-compensation effect. A phase-separation picture with the appearance of ferromagnetic clusters embedded in an antiferromagnetic matrix described the magnetic ground state of the doped samples well. All of the samples exhibited semiconducting behavior over the whole measured temperature range, with the high-temperature behavior better described by the small polaron conduction model and the low-temperature behavior by the two-dimensional version of Mott’s variable range hopping model. A large magnetoresistance effect was observed for all of the doped samples, and its value rose with decreasing temperature and increasing Nb content, attaining 51% at 40 K under a magnetic field of 5 T for the x = 0.2 sample. Calculated results for Ca4Mn3O10 and Ca4Mn2.8Nb0.2O10 samples further verified the corresponding experimental determinations.