Complex-oxide materials exhibit physical properties that involve the interplay of charge and spin degrees of freedom. However, an ambipolar oxide that is able to exhibit both electron-doped and hole-doped ferromagnetism in the same material has proved elusive. Here we report ambipolar ferromagnetism in LaMnO3, with electron-hole asymmetry of the ferromagnetic order. Starting from an undoped atomically thin LaMnO3 film, we electrostatically dope the material with electrons or holes according to the polarity of a voltage applied across an ionic liquid gate. Magnetotransport characterization reveals that an increase of either electron-doping or hole-doping induced ferromagnetic order in this antiferromagnetic compound, and leads to an insulator-to-metal transition with colossal magnetoresistance showing electron-hole asymmetry. These findings are supported by density functional theory calculations, showing that strengthening of the inter-plane ferromagnetic exchange interaction is the origin of the ambipolar ferromagnetism. The result raises the prospect of exploiting ambipolar magnetic functionality in strongly correlated electron systems.

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Ambipolar ferromagnetism by electrostatic doping of a manganite.

The magnetic property of the LaMnO3−δ films was systematically investigated with the variation of the deposited oxygen pressure. The Curie temperature and the saturation magnetization of the films were found increased with the decrease of the oxygen pressure. We believe that the double exchange effect between Mn2+ and Mn3+ ions should be the origin of the ferromagnetism and the enhanced conductivity, where the Mn2+ ions are generated with the oxygen vacancies due to oxygen deficient, and the double-exchange interaction is enhanced with increasing the ratio of Mn2+/Mn3+. The results of the x-ray absorption spectroscopy support our conclusion as well.

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The oxygen vacancy effect on the magnetic property of the LaMnO3−δ thin films

The effects of V doping on field-cooled magnetization MFC(T), zero-field-cooled magnetization MZFC(T), resistivity ρ, thermoelectric power S, and thermal conductivity κ in manganites CaMn1−xVxO3 (0.02⩽x⩽0.08) have been investigated systematically. As the V doping level exceeds 0.02, an anomalous “diamagnetism” has been observed. It is suggested that the force generated by the orbit rotation of eg electron in Mn3+O6 octahedron makes the spin tilt, as a result, the vector sum of individual spins may be along or opposite to the direction of the applied magnetic field, and macroscopically, the average magnetization exhibits positive or negative values. In addition, the transport mechanism in the high and low temperature ranges is dominated by the small polaron conduction and the variable-range-hopping conduction, respectively, according to the fitting analysis of the temperature dependence of Seebeck coefficient S(T) and resistivity ρ(T). Both S and κ peaks appearing at low temperature is gradually suppressed...

Diamagnetism, transport, magnetothermoelectric power, and magnetothermal conductivity in electron-doped CaMn1−xVxO3 manganites

The magnetocaloric effect of an electron-doped manganite La0.9Te0.1MnO3 has been investigated. The sample of La0.9Te0.1MnO3 undergoes the paramagnetic-ferromagnetic transition at 239K. It is obtained that the effective magnetic moment (μeff=4.923μB) and the saturation moment (μS=4.08μB∕Mn) are close to the respective expected values. The isothermal magnetization versus applied magnetic field at various temperatures between 180 and 300K was measured, and the temperature dependence of magnetic entropy change ∣ΔSM∣ for La0.9Te0.1MnO3 was understood. It is found that the sample shows a large magnetic entropy change near TC and the magnitude of magnetic entropy change is comparable to some hole-doped manganites. However, the relative cooling power of the electron-doped manganite La0.9Te0.1MnO3 is higher than that of some hole-doped manganites, which is an advantage for the engineer to design the magnetic refrigeration materials. Moreover, the temperature dependence of magnetic entropy change ∣ΔSM∣ cannot be ex...

Magnetocaloric effect of electron-doped manganite La0.9Te0.1MnO3

The effect of grain size on electrical transport and magnetic properties of La 0.9 Te 0.1 MnO 3.

In this paper, we report the magnetic and electrical properties of the Te-doped lanthanum manganite perovskite compound La 1 - x Te x MnO 3 and the related electron spin resonance (ESR) study. This is a material with rhombohedral structure and it shows good colossal magnetoresistance behavior. The magnetoresistance ratio MR=[ρ(0)-ρ(H)]/ρ(0)is about 63% for x=0.04 in an applied magnetic field of 40 kOe. The resistivity of the compounds is affected by temperature and the amount of Te doping. The temperature dependence of the resistivity showed that the conductivity above the Curie temperature was dominated by the hopping of the small polarons, and the resistance was attributed to the electron-phonon and magnon scattering mechanism below the metal-insulator transition temperature. The ESR investigation indicated that the compound was in the paramagnetic phase above 230 K, and in the single ferromagnetic state below 170 K. In the temperature range of 230 to 170 K, the compound showed phase separation phenomena.

P Duan

Papers

Colossal magnetoresistance behavior and ESR studies of La1-xTexMnO3 (0.04 <= x <= 0.2)