Cu-spin Correlation in the Electron-overdoped High- <i>T</i> _c Cuprate Thin Films of La ₂₋ <i> _x </i> Ce <i> _x </i> CuO ₄ Probed by Low-energy Muons

We investigated the Cu-spin correlation in the overdoped regime of the electron-doped high-<em>T</em>_c cuprate thin films of La₂₋<em>_x</em>Ce<em>_x</em>CuO₄, changing the reduction condition from muon spin relaxation using low-energy muons. The Cu-spin correlation developed at low temperatures for optimally reduced films with <em>x</em> = 0.13 as well as <em>x</em> = 0.17 where the superconductivity was almost suppressed. These results are contrary to those observed in the hole-doped high-<em>T</em>_c cuprates where the development of the antiferromagnetic Cu-spin correlation disappears together with the suppression of superconductivity. The Cu-spin correlation developed at low temperatures in <em>x</em> = 0.17 may be understood in terms of antiferromagnetism, but it may be related to a ferromagnetic order recently suggested in the nonsuperconducting heavily overdoped La₂₋<em>_x</em>Ce<em>_x</em>CuO₄ with <em>x</em> ∼ 0.18.