Magnetic and transport properties in the Ti doped cobaltite Ca3Co4-xTixO9 (0≤x≤0.8) single crystals

Single crystals of Ca3Co4-xTixO9 (x=0, 0.2, 0.4, 0.6, and 0.8) are grown by flux growth technique. The effect of Ti doping at Co site on magnetic and transport properties is studied. All samples show Curie-Weiss behavior at temperatures above 50 K except for the x=0.8 sample, and the effective magnetic moment mu(eff) increases with increasing Ti content. The free-doped sample Ca3Co4O9 shows a ferrimagnetic transition at 19 K. However, a spin-glass transition at T-f(similar to 20 K) appears for the Ti doped samples and the transition temperature T-f shifts to higher temperature as the Ti content increases. The magnetic moment values M at T-f and 5 K under the applied field of 4.5 T increase with increasing Ti doping content. The variation of the magnetic properties may be related to the induced extra Co2+ ions in the CoO2 layer by substituting Ti4+ for Co3+. The resistivity rho of the x=0, 0.2, 0.4, and 0.6 samples shows metalliclike behavior at high temperatures and a broad metal-insulator (M-I) transition appears as the temperature decreases to a certain value T-min. The value of resistivity and the ratio of rho(5 K)/rho(300 K) increase with increasing Ti content. The results are discussed according to the decrease of charge carrier concentration in the samples, which is confirmed by the Hall coefficient measurement. For the x=0.8 sample, there exists another M-I transition in the vicinity of 269 K, which is suggested to originate from the spin-state transition of Co3+ or Co4+ ions. (c) 2006 American Institute of Physics.