Ru(4+) induced colossal magnetoimpedance in Ru doped perovskite manganite at room temperature.

We have demonstrated Ru(4+) induced colossal magnetoimpedance (MI) at room temperature in a ∼1 Tesla magnetic field with a pulsed laser deposited La0.7Ca0.3Mn0.7Ru0.3O3 thin film. This composition showed a large negative ∼12% MI in the low frequency range (<5 MHz), a colossal positive MI > 120% in the intermediate frequency range (5 MHz to ∼13 MHz) and a negative MI in the high frequency range (∼13 MHz to 40 MHz) at room temperature. XAS data confirmed the predominant Ru valence state was 4+ in La0.7Ca0.3Mn0.7Ru0.3O3. Ru(4+) induced (i) charge carrier localization and (ii) reduced hole carrier density enhances the MI in this composition, which otherwise was not significant in mixed valences Mn(3+)/Mn(4+) containing La0.7Ca0.3MnO3 and Ru(4+)/Ru(5+) and Mn(3+)/Mn(4+) mixed valences containing Ru = 0.1 and Ru = 0.2 compositions in La0.7Ca0.3Mn1-xRuxO3 (0 ≤x≤ 0.3) thin films.