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

本课题的目标是合成室温铁磁介质薄膜，该薄膜有可能应用于新型磁介电器件。以下是项目中获得的主要成果。(1)利用脉冲激光沉积技术在（001）SrTiO_3衬底上成功制备了BaFe_<1-x>Zr_x0_<3-δ> (x=0.0 ~ 0.8)单晶薄膜。在x=0.7样品的偏置电场为150 kV/cm时，薄膜的漏电流密度可达1.1x10^<-5> A/cm^2。这远远小于BaFe0_<3-δ>单晶薄膜的10^<-4>，这表明锆取代明显改善了薄膜的介电性能。在5k下测量的x=0.7样品的磁化回路清楚地显示出滞后以及残余磁化的存在。因此，x=0.7样品的磁性有序度已经大大增强，可能是由于铁磁性spi…值得一提的是，x=0.7的样品在室温下仍然表现出铁磁特性。因此，在不久的将来，BaFe_<0.3>Zr_<0.7>0_<3-δ>是实际应用于某些磁电器件的潜在候选材料，例如铁电-铁磁栅极场效应晶体管。(2)成功合成了具有准立方晶体结构的Ba(Co_<1-x>Mn_x) _<3-δ> （x=0.2和0.7）单晶薄膜。发现薄膜具有高电阻性，在5k时介电常数为ε=5.2。相反，薄膜在室温下表现出类似半导体的导电行为。室温下，饱和磁化强度为1.20 μB/fu的x=0.2样品可实现铁磁有序，而饱和磁化强度为1.41 μB/fu的x=0.7样品可实现铁磁有序。观察到的磁有序可能是由于Mn4+(d3)-O2—Co4+(d5)离子的超交换偶联，成键角为180度。少

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