10:45 AM - 11:00 AM
△ [19a-H111-8] Giant positive magnetoresistance in perovskite SrNbO2N epitaxial thin film
Keywords:Perovskite oxynitride,Giant magnetoresistance,Anderson localization
[Introduction] Perovskite oxynitride ABO3−xNx is expected as a new group of electronic materials because their unique electrical properties including high dielectric constant and negative giant magnetoresistance have been reported. However, the detailed mechanisms to cause such functionalities have not been understood well due to the difficulty in synthesizing highly dense specimens suitable for accurate electrical measurements. We have been addressing this issue by synthesizing high quality epitaxial thin films of perovskite oxynitrides with nitrogen plasma assisted pulsed laser deposition. Previously, we have reported synthesis of a series of SrNbO3−xNx (0 ≤ x ≤ 1) epitaxial thin films and systematic control of carrier density in them with nitrogen content x. Because nitrogen ions are introduced to the -O-B-O- network in perovskite oxynitrides, nitrogen content x can influence not only carrier density but also the periodic potential in them. In this study, we investigated temperature and magnetic field dependence of resistivity of the SrNbO3−xNx epitaxial thin films and discussed the influence of nitrogen introduction on electrical conduction mechanism.
[Film synthesis] SrNbO3−xNx thin films were grown on the (100) plane of KTaO3 single crystals at substrate temperature of 630 °C using a Sr2Nb2O7 ceramic pellet as target. Nitrogen gas activated by electron cyclotron resonator (ECR) was introduced to the growth chamber during film deposition and the nitrogen content x in the films was controlled by changing the in-put current of ECR. X-ray diffraction confirmed (001) oriented epitaxial growth of perovskite SrNbO3−xNx.
[Electrical transport property] The end member SrNbO3 showed low resistivity ρ in the order of 10−5 to 10−6 Ωcm and metallic temperature dependence (dρ/dT > 0). With increasing nitrogen content x, the temperature dependence of ρ became semiconductive (dρ/dT < 0) and electron carriers, plausibly generated by oxygen vacancies, showed insulating behavior represented by variable range hopping model in SrNbO2N (x = 1.02). Furthermore, positive magnetoresistance was observed at low temperature and was enhanced with increasing nitrogen content x. The SrNbO2N epitaxial film showed a large magnetoresistance value of 50% at 2 K and 9 T and its magnetic field dependence was well fitted by the function of the wave-function shrinkage model. These results indicate that nitrogen introduction caused extreme localization of electron carriers. Because this localization effect reflects the long range randomness of nitrogen and oxygen ions, which is a characteristic of oxynitrides, this study would be a guidepost for future investigations on electrical conduction in oxynitride compounds.
[Film synthesis] SrNbO3−xNx thin films were grown on the (100) plane of KTaO3 single crystals at substrate temperature of 630 °C using a Sr2Nb2O7 ceramic pellet as target. Nitrogen gas activated by electron cyclotron resonator (ECR) was introduced to the growth chamber during film deposition and the nitrogen content x in the films was controlled by changing the in-put current of ECR. X-ray diffraction confirmed (001) oriented epitaxial growth of perovskite SrNbO3−xNx.
[Electrical transport property] The end member SrNbO3 showed low resistivity ρ in the order of 10−5 to 10−6 Ωcm and metallic temperature dependence (dρ/dT > 0). With increasing nitrogen content x, the temperature dependence of ρ became semiconductive (dρ/dT < 0) and electron carriers, plausibly generated by oxygen vacancies, showed insulating behavior represented by variable range hopping model in SrNbO2N (x = 1.02). Furthermore, positive magnetoresistance was observed at low temperature and was enhanced with increasing nitrogen content x. The SrNbO2N epitaxial film showed a large magnetoresistance value of 50% at 2 K and 9 T and its magnetic field dependence was well fitted by the function of the wave-function shrinkage model. These results indicate that nitrogen introduction caused extreme localization of electron carriers. Because this localization effect reflects the long range randomness of nitrogen and oxygen ions, which is a characteristic of oxynitrides, this study would be a guidepost for future investigations on electrical conduction in oxynitride compounds.