Slow antiferromagnetic dynamics in the low-temperature tetragonal phase of La{sub 2{minus}x}Sr{sub x}CuO{sub 4} 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 La{sub 2{minus}x}Sr{sub x}CuO{sub 4}. The data give evidence that at particular levels of Sr and Eu doping the frequency of the antiferromagnetic fluctuations {omega}{sub 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{ge}8 K, in contrast to the observation by neutron scattering of stripe ordering of spins below 50 K in a Nd-doped La{sub 2{minus}x}Sr{sub x}CuO{sub 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. {copyright} {ital 1997} {ital The American Physical Society}