Magnetic Neutron Scattering Study of Rare-Earth Titanates

The Mott-insulating rare-earth (R) titanates (RTiO₃) are known to host ferromagnetic-antiferromagnetic transitions in solid-solution systems such as Y_1-xLa_xTiO₃, as well as metal-insulator transitions in charge carrier-doped systems such as Y_1-xCa_xTiO₃. Neutron scattering studies have been largely restricted to the undoped YTiO₃ and LaTiO₃. Here, we report on our neutron scattering work on the magnetic order and excitations in the doped systems Y_1-xLa_xTiO₃ and Y_1-xCa_xTiO₃, using triple-axis spectrometry and small-angle neutron scattering (SANS). We find a strong reduction in the transition temperature and ordered magnetic moment, but accompanied by very little change in the spin-wave dispersion in the Y_1-xLa_xTiO₃ system as we approach the critical doping x~0.3. SANS results suggest a rotation of the easy axis with substitution, development of magnetic inhomogeneities on ~10 nm scales, and distinct changes in critical scattering as the magnetic crossover is approached. These results suggest significant changes in the magnetic ground state as one approaches the crossover. Initial studies on the Y_1-xCa_xTiO₃ system will also be reported.