Studies on control of spin ordering in magneto-dielectric thin films and their application for future electronics devices

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The target of this research project is to synthesize room-temperature ferromagnetic dielectric thin films, which can possibly apply for novel magneto-dielectric devices. The followings are the main results obtained in the projects.(1)The single crystalline BaFe_<1-x>Zr_x0_<3-δ> (x=0.0-0.8) thin films were successfully produced on (001) SrTiO_3 substrates by pulsed laser-beam deposition. The films were found to be highly resistive, up to the leakage current density of about 1.1x10^<-5> A/cm^2 at the bias electric field of 150 kV/cm for the x=0.7 sample. This is much less than 10^<-4> of that for the BaFe0_<3-δ>, single crystalline film, which implies that the dielectric properties have been distinctly improved by zirconium substitution. The magnetization loop measured at 5 K for the x=0.7 sample clearly shows hysteresis as well as the presence of the remanent magnetization. Hence, the magnetic ordering for the x=0.7 sample has been greatly enhanced, possibly due to the ferromagnetic spi … More n alignment of Fe ions. It should be worthwhile mentioning that the x=0.7 sample still exhibits a ferromagnetic characteristic at room temperature. Consequently, BaFe_<0.3>Zr_<0.7>0_<3-δ> is a potential candidate for practical use in some magnetoelectric devices, such as a ferroelectric-ferromagnetic gate field-effect-transistor in the near future.(2)The single crystalline Ba(Co_<1-x>Mn_x)0_<3-δ> (x=0.2 and 0.7) films with the pseudo-cubic crystal structure were successfully synthesized. The films were found to be highly resistive with a dielectric constant of ε=5.2 at 5 K. In contrast, the films exhibited semiconductor-like conduction behavior at room temperature. Room temperature ferromagnetic ordering can be realized in samples with a saturation magnetization of 1.20 μB/fu for the x=0.2 sample, in contrast to 1.41 μB/fu for the x=0.7 sample. A possible origin of the observed magnetic ordering may be due to the superexchange coupling of Mn4+(d3)-O2--Co4+(d5) ions with a bonding angle of 180 degrees. Less