  Antiferromagnetic (AF) spin fluctuations are commonly believed to play a key
role in electron pairing of cuprate superconductors. In electron-doped
cuprates, it is still in paradox about the interplay among different electronic
states in quantum perturbations, especially between superconducting and
magnetic states. Here, we report a systematic transport study on
cation-optimized La2-xCexCuO4 (x = 0.10) thin films in high magnetic fields. We
find an AF quantum phase transition near 60 T, where the Hall number jumps from
nH =-x to nH = 1-x, resembling the change of nH at the AF boundary (xAF = 0.14)
tuned by Ce doping. In the AF region a spin dependent state manifesting
anomalous positive magnetoresistance is observed, which is closely related to
superconductivity. Once the AF state is suppressed by magnetic field, a
polarized ferromagnetic state is predicted, reminiscent of the recently
reported ferromagnetic state at the quantum endpoint of the superconducting
dome by Ce doping. The magnetic field that drives phase transitions in a
similar but distinct manner to doping thereby provides a unique perspective to
understand the quantum criticality of electron-doped cuprates.
