Precursor diamagnetism above the superconducting transition inLa1.9Sr0.1CuO4

High-resolution isothermal magnetization curves above the transition temperature ${T}_{c}$ in a single crystal of superconducting underdoped cuprate ${\mathrm{La}}_{1.9}{\mathrm{Sr}}_{0.1}{\mathrm{CuO}}_{4}$ ${(T}_{c}=26\mathrm{K})$ are reported. For magnetic field $Hg~1\mathrm{kOe}$ the diamagnetic magnetization is rather well described by the Ginzburg-Landau theory in finite fields, as observed in previous works. On the contrary, in the low-field range and for T within ${T}_{c}+2\mathrm{K},$ evidence is given for precursor diamagnetism of different character, with magnetization curves displaying an upturn in the field dependence and magnetic-history dependent effects below $T\ensuremath{\simeq}27\mathrm{K}.$ These findings are the magnetic counterpart of the observation by scanning superconducting quantum interference device microscopy of regions precursor of bulk superconductivity. The interpretation of the experimental data in terms of phase fluctuations of local order parameter is shown to account for most of the aspects of the precursor diamagnetism, which appears to be a general phenomenon in cuprates.