Slow antiferromagnetic dynamics in the low-temperature tetragonal phase ofLa2−xSrxCuO4as revealed by ESR of Gd spin probes

Abstract

Measuring the electron spin resonance 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 ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$. The data give evidence that at particular levels of Sr and Eu doping the frequency of the antiferromagnetic fluctuations ${\mathrm{\omega }}_{\mathrm{sf}}$ 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⩾8 K, in contrast to the observation by neutron scattering of stripe ordering of spins below 50 K in a Nd-doped ${\mathrm{La}}_{2\mathrm{-}\mathrm{x}}$ ${\mathrm{Sr}}_{\mathrm{x}}$ ${\mathrm{CuO}}_4$ single crystal. In 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 characteristic property of the magnetism in the LTT structural phase may not be static magnetic order at elevated temperatures but rather extremely slow antiferromagnetic dynamics.