Critical behavior inLaTiO3+δ/2in the vicinity of antiferromagnetic instability

The critical behavior in the vicinity of antiferromagnetic instability has been investigated for the filling-controlled insulator-metal transition system, ${\mathrm{LaTiO}}_{3+\delta /2\mathrm{}},$ by transport and specific heat measurements. With the increase of nominal hole doping $\delta ,$ the system undergoes a phase change from an insulating phase to a metallic phase at ${\delta }_c^{\mathrm{IM}}\approx 0.05$ and the low-temperature antiferromagnetic phase disappears at ${\delta }_c^{\mathrm{mag}}\approx \mathrm{0.08.}$ The Hall coefficient for an antiferromagnetic metallic crystal of $\delta \approx 0.06$ shows a broad minimum near the Néel temperature while that for the compound of $\delta ={\delta }_c^{\mathrm{mag}}$ exhibits little temperature variation. At the antiferromagnetic instability point, the electronic specific heat coefficient $\gamma$ as well as the coefficient $\beta$ of $T^3$ term of specific heat takes a maximum value as a function of $\delta .$ High-pressure measurements of resistivity and Hall coefficient revealed that not only the antiferromagnetic spin correlation but also randomness effect plays an important role in producing an unconventional metallic state in the immediate vicinity of the magnetic instability point of the present compound.