Slow antiferromagnetic dynamics in the low temperature tetragonal phase of La_{2-x}Sr_xCuO_4 as revealed by ESR of Gd spin probes

TL;DR

This study uses ESR of Gd probes to reveal extremely slow antiferromagnetic dynamics in the low temperature tetragonal phase of La_{2-x}Sr_xCuO_4, contrasting with static order observed in related compounds.

Contribution

It demonstrates that the LTT phase exhibits slow antiferromagnetic fluctuations rather than static magnetic order at temperatures above 8K, challenging previous neutron scattering findings.

Findings

Antiferromagnetic fluctuation frequency decreases by nearly three orders of magnitude at low temperatures.

No static magnetic order detected above 8K in the studied LTT phase.

Static order in Nd-doped compounds likely results from rare earth and Cu spin interactions.

Abstract

Measuring the ESR of Gd spin probes we have studied the magnetic properties of the copper oxide planes in the low temperature tetragonal (LTT) phase of Eu doped La_{2-x}Sr_xCuO_4. The data give evidence that at particular levels of Sr and Eu doping the frequency of the antiferromagnetic fluctuations in the LTT phase dramatically decreases at low temperatures by almost three orders of magnitude. However, no static magnetic order has been found for T>8K in contrast to the observation by neutron scattering of stripe ordering of spins below 50K in a Nd doped La_{2-x}Sr_xCuO_4 single crystal. To our opinion static order in the Nd doped compound is induced due to the interaction between the Cu spins with the rare earth magnetic moments. Therefore, a really characteristic property of the magnetism in the LTT structural phase may be not static magnetic order at elevated temperatures but rather extremely slow antiferromagnetic dynamics.