Lattice and magnetic dynamics in perovskite Y1−xLaxTiO3

Abstract

Inelastic neutron scattering combined with the dynamic pair density function (DPDF) analysis were used to investigate the magnetic and lattice dynamics in the orbitally active ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{TiO}}_{3}$ as it crosses the antiferromagnetic (AFM) to ferromagnetic (FM) phase boundary. Upon doping, the FM state present in ${\mathrm{YTiO}}_{3}$ is suppressed on approaching a critical concentration of ${x}_{c}\ensuremath{\sim}0.3$ in which ${T}_{C}\ensuremath{\simeq}0$, and is replaced by the AFM phase of ${\mathrm{LaTiO}}_{3}$. Below ${x}_{c}$, magnetic scattering from spin waves is dominant at low energies. At ${x}_{c}$ with a ${T}_{C}\ensuremath{\simeq}0$, magnetic scattering is also observed and is most likely due to AFM fluctuations. At the same time, local atomic fluctuations extending to 50 meV are observed above and below the magnetic transitions from $0\ensuremath{\le}x\ensuremath{\le}1$ that show distinct characteristics with $x$. From Y to La, a clear difference is observed in the phonon density of states as a function of doping as well. At $x=0.15$ and 0.3, low-energy modes involving predominantly the rare-earth ion become suppressed with increasing temperature, while in $x=1$, strong suppression of phonon modes across a wide range in energy is observed above ${T}_{N}$. It is likely that in the Y heavy samples, phonon modes below 20 meV have a stronger influence on the orbital excitations, while in ${\mathrm{LaTiO}}_{3}$, a strong phonon dependence is observed upon cooling up to ${T}_{N}$.