Effect of electric field doping on the anisotropic magnetoresistance in doped manganites

We have modulated the anisotropic magnetoresistance (AMR) in $3–4\mathrm{nm}$ manganite films using the ferroelectric field effect—a method that electrostatically varies the carrier density without affecting the lattice distortion. While significant changes have been induced in $T_C$ and $\rho$, the AMR ratio remains the same when the magnetic state is not changed. This scaling behavior is in striking contrast to chemical doping results, where similar modulation of the carrier concentration $(\sim 0.1∕\mathrm{Mn})$ changes the AMR ratio by $⩾30\%$. The results reveal unambiguously the dominant role of chemical distortion in determining the AMR in manganites.

Figure 1

(Color) (a) Hall bar configuration used for the experiment; (b) resistivity of a $3\mathrm{nm}$ ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}\mathrm{Mn}{\mathrm{O}}_3$ film in a PZT/LSMO heterostructure as a function of temperature for accumulation (black) and depletion (red) states; (c) magnetoresistance as a function of magnetic field at $175\mathrm{K}$ in accumulation (black) and depletion (red); (d) magnetoresistance ratio at $80\mathrm{kOe}$ as a function of temperature in accumulation (black) and depletion (red).

Figure 2

(Color) The angular dependence of ${\rho }_{\mathrm{AMR}}$ at $150\mathrm{K}$ and $20\mathrm{kOe}$ (symbols) for accumulation (black) and depletion (red) states, along with fits to $\cos 2\theta$ (dashed lines).

Figure 3

(a) $\Delta {\rho }_{\mathrm{AMR}}$ as a function of temperature for accumulation (solid) and depletion (open) states; (b) ${\Delta }_{\mathrm{AMR}}$ at $20\mathrm{kOe}$ as a function of temperature for accumulation (solid) and depletion (open) states.

Figure 4

(Color) Field dependence of ${\Delta }_{\mathrm{AMR}}$ for accumulation (solid) and depletion (open) states at $125\mathrm{K}$ (red squares), $250\mathrm{K}$ (blue diamonds), and $275\mathrm{K}$ (green triangles).

Figure 5

(Color) Temperature dependence of ${\Delta }_{\mathrm{AMR}}$ at $7\mathrm{kOe}$ for accumulation (solid) and depletion (open) states taken on LSMO heterostructures with $x=0.33$ (red) and 0.16 (green), and a ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_3$ heterostructure (blue);

Figure 6

Maximum ${\Delta }_{\mathrm{AMR}}$ measured as a function of the tolerance factor for LSMO and LCMO heterostructures (solid) and single layer films (open).