Electronic phase separation in the rare earth manganates, (La1-xLnx)0.7Ca0.3MnO3 (Ln = Nd, Gd and Y)

TL;DR

This study investigates phase separation and magnetic-electrical behavior in La1-xLnx)0.7Ca0.3MnO3 manganates, revealing how composition and cation size disorder influence ferromagnetism, insulator-metal transitions, and dielectric properties.

Contribution

It provides new insights into the relationship between A-site cation size, disorder, and phase separation in manganates, highlighting the critical radius and disorder effects on magnetic and electronic phases.

Findings

Ferromagnetic Tc decreases with x up to a critical value xc.

Phase separation occurs around xc, affecting magnetic and electrical properties.

High dielectric constants are observed in insulating regimes at certain temperatures.

Abstract

All the three series of manganates showsaturation magnetization characteristic of ferromagnetism, with the ferromagnetic Tc decreasing with increasing in x up to a critical value of x, xc (xc = 0.6, 0.3, 0.2 respectively for Nd, Gd, Y). For x > xc, the magnetic moments are considerably smaller showing a small increase around TM, the value of TM decreasing slightly with increase in x or decrease in < rA >. The ferromagnetic compositions (x xc) show insulator-metal (IM) transitions, while the compositions with x > xc are insulating. The magnetic and electrical resistivity behavior of these manganates is consistent with the occurrence of phase separation in the compositions around xc, corresponding to a critical average radius of the A-site cation, < rAc >, of 1.18 A. Both Tc and TIM increase linearly when < rA > > < rAc > or x xc as expected of a homogenous ferromagnetic phase. Both Tc and TM decrease linearly with the A-site cation size disorder at the A-site as measured by the variance s2. Thus, an increase in s2 favors the insulating AFM state. Percolative conduction is observed in the compositions with < rA > > < rAc >. Electron transport properties in the insulating regime for x > xc conforms to the variable range hopping mechanism. More interestingly, when x > xc, the real part of dielectric constant (e') reaches a high value (104-106) at ordinary temperatures dropping to a very small (~500) value below a certain temperature, the value of which decreases with decreasing frequency.