Griffiths singularities and magnetoresistive manganites

TL;DR

This paper investigates the magnetic and thermodynamic behavior of doped manganites with varying transition temperatures, revealing Griffiths phase features and unusual magnetic properties extending above the transition temperature.

Contribution

It demonstrates the presence of Griffiths phase behavior in manganites and links magnetic anomalies to dopant-induced variations in transition temperature.

Findings

Unusual magnetic properties extend more than 100 K above the transition.

Griffiths phase behavior is observed in doped manganites.

Transition temperature depression is linked to random bond-angle bending.

Abstract

The large, so-called colossal, magnetoresistivity of doped manganese oxides based on LaMnO3 has attracted considerable attention, but only one unusual feature of the ferromagnetic transition in these compounds. We examine in this paper the progression of magnetic and thermodynamic behavior as the transition temperature is made to vary from 360 K to 218 K by changing the divalent dopant. Single crystals of La_{0.7}Sr_{0.3}MnO3, as is well known, show modest magnetoresistivity and conventional critical behavior. La$_{0.7}$Pb$_{0.3}$ Mn$O_3$, and to an even greater extent, La$_{0.7}$Ca$_{0.3}$MnO$_3$, have unusual magnetic properties extending more than 100 K above the transition. We treat the properties of the latter samples in the context of a Griffiths phase in which the transition temperature is depressed from its maximum value T_{G} by random bond-angle bending.