Strong enhancement of spin fluctuations in the low-temperature tetragonal phase of antiferromagnetically ordered La2-x-yEuySrxCuO4

Measurements of the static magnetization, susceptibility and electron spin resonance (ESR) of Gd spin probes have been performed to study the properties of antiferromagnetically ordered La2-x-yEuySrxCuO4 (x0.02) with the low-temperature tetragonal structure. According to the static magnetic measurements, the CuO2 planes are magnetically decoupled in this structural phase. The ESR study reveals strong magnetic fluctuations at the ESR frequency which are not present in the orthorhombic phase. It is argued that this drastic enhancement of the spin fluctuations is due to a considerable weakening of the interlayer exchange and a pronounced influence of hole motion on the antiferromagnetic properties of lightly hole-doped La2CuO4. No evidence for the stripe phase formation at small hole doping is obtained in the present study.