Slow antiferromagnetic dynamics in the low-temperature tetragonal phase of La2-xSrxCuO4 as revealed by ESR of Gd spin probes
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 La2-xSrxCuO4. The data give evidence that at particular levels of Sr and Eu doping the frequency of the antiferromagnetic fluctuations ωsf 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 La2-xSrxCuO4 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.