Unconventional ferromagnetism in epitaxial (111) LaNiO 3

We report the observation of ferromagnetism in thin films of paramagnetic metal ${\mathrm{LaNiO}}_{3}$ grown on nonmagnetic insulating substrate ${\mathrm{LaAlO}}_{3}$(111) substrates. The films exhibit a large hysteresis loop on magnetoresistance and anomalous Hall effect as well as sixfold anisotropic magnetoresistance. Together with the ferroelectricity and inversion symmetry breaking reported in the same system, these results suggest that, by the geometric constraints by the substrate, paramagnetic metals can turn into ferromagnetic semiconductors. The ferromagnetic ground state is consistent with the predicted spin-split Fermi surfaces of spin-orbit-coupled correlated metals. Moreover, our results reveal a positive linear magnetoresistance and a sign reversal of hysteresis loop, which is consistent with the existence of a massive Dirac point as predicted by theories.