Comparative study of specific heat measurements in LaMnO3, La1.35Sr1.65Mn2O7, La1.5Sr0.5NiO4 and La1.5Sr0.5CoO4

TL;DR

This study compares the specific heat behavior of various La-based manganite and nickelate crystals under different magnetic fields, revealing effects of magnetic field suppression, electronic interactions, and anisotropy gaps at low temperatures.

Contribution

It provides detailed measurements of specific heat in multiple La-based compounds, highlighting magnetic field effects and low-temperature excitations not previously characterized.

Findings

Spin-wave excitations suppressed by 9 T in La1.35Sr1.65Mn2O7

Magnetic field had no effect on other samples' specific heat

Evidence of anisotropy gap in La1.35Sr1.65Mn2O7 and La1.5Sr0.5NiO4

Abstract

We present the temperature dependence of the specific heat, without external magnetic field and with H= 9 T, for LaMnO3, La1.35Sr1.65Mn2O7, La1.5Sr0.5NiO4 and La1.5Sr0.5CoO4 single crystals. We found that spin-wave excitations in the ferromagnetic and bilayer-structure La1.35Sr1.65Mn2O7 were suppressed by the 9 T magnetic field. On the other hand, the external magnetic field had no effect in the specific heat of the other three antiferromagnetic samples. Also, the electronic part of the interactions were removed at very low temperatures in the La1.5Sr0.5NiO4 single crystal, even with a zero applied magnetic field. Below 4 K, we found that the specific heat data for La1.35Sr1.65Mn2O7 and La1.5Sr0.5NiO4 crystals could be fitted to an exponential decay law. Detailed magnetization measurements in this low temperature interval showed the existence of a peak close to 2 K. Both results, magnetizations and specific heat suggest the existence of an anisotropy gap in the energy spectrum of La1.35Sr1.65Mn2O7 and La1.5Sr0.5NiO4 compounds.