Role of charge doping and distortions on the structural, electrical and magnetic properties of modified CuFeO_2 compounds

摘要

Single phase CuFeO_2, CuFe_(0.96)M_(0.03)V_(0.01)O_2 (M = Ti, Mn, and Ga), and CuFe_(0.96)V_(0.04)O_2 compounds with space group R3m were prepared through a newly developed solid-state technique using annealing under high vacuum. Raman studies demonstrate, for the first time, a minor shift in Ti and Mn-doped samples as well as the Jahn-Teller effect induced distortions around 500 cm~(-1) along with well-documented peaks of E_g and A_(1g) modes. Mossbauer studies confirm the presence of iron in high spin Fe~(3+) and quadruple splitting values endorsing the presence of octahedron distortions. An increase in the electrical conductivity at low temperatures is observed due to the enhanced charge doping with minor variations related to local distortions. Low-temperature magnetic studies of pristine and Ti-doped samples demonstrate paramagnetic nature up to 25 K. However, on one hand, the pristine sample shows a sharp rise in magnetization values at low applied fields and on the other side, Ti-doped samples exhibit nearly linear behavior. Dielectric measurements confirm weakening of electrical ordering near the magnetic transition in distorted Ti-doped samples, compared to pure CuFeO_2 sample. Level of charges along with its local distortions affected mobility has significant effects on transport and multiferroic nature of these samples.