  We report neutron scattering studies on single crystals of the electron-doped
(n-type) superconducting cuprate Nd2-xCexCuO4 (x=0.15) with Tc = 18 K and 25 K.
Unlike the hole-doped (p-type) superconducting cuprates where incommensurate
magnetic fluctuations commonly exist, the n-type cuprate shows commensurate
magnetic fluctuations at the tetragonal (1/2 1/2 0) reciprocal points both in
the superconducting and in the normal state. A spin gap opens up when the
n-type cuprate becomes superconducting, as in the optimally doped p-type
La2-xSrxCuO4. The gap energy, however, increases gradually up to about 4 meV as
T decreases from Tc to 2 K, which contrasts with the spin pseudogap behavior
with a T-independent gap energy in the superconducting state of p-type
cuprates.
