AC magnetic behavior of large grain magneto-resistive La0.78Ca0.22Mn0.90Ox materials

TL;DR

This study investigates the AC magnetic behavior of large grain La-Ca-Mn-O materials with different microstructures, revealing how superimposed DC fields and microstructure influence magnetic transitions and critical exponents.

Contribution

It provides a detailed analysis of AC magnetic susceptibility in large grain La-Ca-Mn-O samples with varying microstructures, highlighting the effects of microstructure and DC fields on magnetic transitions.

Findings

Single and polycrystalline samples show a single susceptibility peak.

Double grain samples exhibit an additional kink in susceptibility.

Critical exponents are close to mean-field model values across samples.

Abstract

We report a detailed set of AC magnetic measurements carried out on bulk large grain La-Ca-Mn-O samples extracted from a floating zone method-grown rod. Three samples with $La_{0.78}Ca_{0.22}Mn_{0.90}O_{x}$ stoichiometry but differing in their microstructure were investigated by electrical resistivity and AC susceptibility measurements: (i) a single grain sample, (ii) a sample containing two grains and (iii) a polycrystalline sample. We show that the superimposition of DC magnetic fields during AC magnetic susceptibility measurements is an efficient way for characterizing the magnetic transition of samples with different microstructures. Whereas both single grain and polycrystalline samples display a single susceptibility peak, an additional kink structure is observed in the case of the double grain sample. The temperature dependence of the AC susceptibility measured with superimposed DC magnetic fields is analyzed in the framework of second-order phase transition ideas. The relations between the critical exponents ($\beta + \gamma$ ~ 1.5, $\delta$ ~ 2.5) are found to be close to those of the mean-field model for all samples. This is attributed to the disordering caused by unoccupied Mn sites.