La0.7Ca0.3MnO3薄膜庞磁电阻(CMR)现象的分析

针对La0.7Ca0．3MnO3薄膜材料中磁团簇的特性及其对材料庞磁电阻(CMR)现象的影响进行了研究。根据实验数据，利用Wagner等提出的数学模型，对La0.7Ca0.3MnO3薄膜中的磁团簇随温度的变化行为特性进行了研究；通过对La0.7Ca0．3MnO3薄膜相关实验数据的拟合，发现La0．7Ca0．3MnO3薄膜的居里温度范围应当在245～250K之间，从而进一步缩小了该材料居里温度的误差范围；还通过计算MR随磁团簇总角量子数J的变化，研究了制约和影响MR值的主要因素，发现磁团簇尺寸在La0．7Ca0.3MnO3薄膜的CMR现象中扮演了重要角色。     

Zero—field—cooled and field—cooled magnetizations and magnetic susceptibility of itinerant ferromagnet SrRuO3

Zero-field-cooled(ZFC) magnetization,field-cooled(FC) magnetization,ac magnetic susceptibility and major hysteresis loops of itinerant ferromagnet SrRuO3 have been measured at magnetic ordering temperatures ranging from 5 to 160K.An empirical model is proposed to calculate the measured ZFC magnetization.The result indicates that the calculated ZFC magnetization compares well with the measured one.Based on the generalized Preisach model.both the ZFC and FC curves are reproduced by numerical simulations.The critical temperature and critical exponents are determined by measuring the ac magnetic susceptibility in different bias magnetic fields at temperatures in the vicinity of the point of phase transition.     

Reactively sputtered Fe3 O4 -based films for spintronics

Half metallic polycrystalline, epitaxial Fe3O4 films and Fe3O4 -based heterostructures for spintronics were fabricated by DC reactive magnetron sputtering. Large tunneling magnetoresistance was found in the polycrystalline Fe3O4 films and attributed to the insulating grain boundaries. The pinning effect of the moments at the grain boundaries leads to a significant exchange bias. Frozen interfacial/surface moments induce weak saturation of the high-field magnetoresistance. The films show a moment rotation related butterfly-shaped magnetoresistance. It was found that in the films, natural growth defects, antiphase boundaries, and magnetocrystalline anisotropy play important roles in high-order anisotropic magnetoresistance. Spin injection from Fe3O4 films to semiconductive Si and ZnO was measured to be 45% and 28.5%, respectively. The positive magnetoresistance in the Fe3O4 -based heterostructures is considered to be caused by a shift of the Fe3O4 e g ↑ band near the interface. Enhanced magnetization was observed in Fe3O4 /BiFeO 3 heterostructures experimentally and further proved by first principle calculations. The enhanced magnetization can be explained by spin moments of the thin BiFeO 3 layer substantially reversing into a ferromagnetic arrangement under a strong coupling that is principally induced by electronic orbital reconstruction at the interface.     

退火Co/C软X射线多层膜中碳的TEM和Raman散射研究

用透射电子显微镜(TEM)和Raman散射(RS)研究了对向靶溅射法制备的Co/C软X射线多层膜在退火条件下碳的结构变化.结果表明,碳层的结构变化可大致分为三个阶段,即有序化,结晶以及晶粒生长阶段。在退火温度低于400℃时的有序化阶段,非晶碳层中键角无序的三配位键和四配位键转变为理想的三配位键。在结晶阶段,非晶碳层在500～600℃的退火温度下结晶成为石墨微晶。在晶粒生长阶段,样品在700℃以上温度退火,石墨微晶尺寸增大,与TEM分析结果相一致。     

高温超导体中磁通涡旋的量子隧道效应——TlBaCaCuO化合物磁弛豫的实验研究

本文报道了ＴｌＢａＣａＣｕＯ超导体（２２１２，２２２３单相，多晶及薄膜材料）中磁弛豫现象的实验结果。从实验上证实了通量运动由热激活到非热激活机制的转变。实验中得到的与温度无关的磁弛豫速率与由通量运动量子隧道效应理论计算结果相一致。同时讨论了各向异性和磁场对磁通的量子漂移速率的影响     

高热稳定性CoN/CN软X射线多层膜的制备及其结构稳定性研究

研究了对向靶反应溅射法制备的CoN/CN软X射线多层膜的结构稳定性。研究表明,通过掺杂N原子可以将Co/C软X射线多层膜的结构稳定性提高100～200℃.400℃温度下退火,CoN/CN多层膜的周期膨胀仅为4%,700℃时周期结构仍然存在.N掺杂可以有效抑制CN层中sp³键的形成,延迟层内结晶过程,进而减小了周期膨胀.Co-N和C-N间存在的强化学键可以减小结构弛豫.填隙N原子增大了Co原子运动的粘滞性,使hcp-Co和fcc-Co在相变温度以上共存,抑制了高温下晶粒长大.     

高温超导体中磁通涡旋的量子隧道效应——TlBaCaCuO化合物磁弛豫的实验研究

本文报道了ＴｌＢａＣａＣｕＯ超导体（２２１２,２２２３单相,多晶及薄膜材料）中磁弛豫现象的实验结果。从实验上证实了通量运动由热激活到非热激活机制的转变。实验中得到的与温度无关的磁弛豫速率与由通量运动量子隧道效应理论计算结果相一致。同时讨论了各向异性和磁场对磁通的量子漂移速率的影响     

热处理Co/C软X射线多层膜的掠入射反射率增强

研究了低温退火Co/C软X射线多层膜中掠入射反射率的增强现象．通过测量一级调制峰强度随退火温度和时间的变化，测得了低至-10^-25m²s^－1的有效扩散系数．由于所研究的Co/C多层膜的调制波长远大于Co-C系统的扩散临界波长，有效扩散系数近似等于真实宏观扩散系数．负的宏观扩散系数表明，在Co-C系统中有相分离的趋势．这一结果可解释为由Miedema宏观原子模型计算得到的正的Co-C系统的混合焓．高退火温度下反射率的降低是界面锐化与界面粗糙化 关键词：     

巡游磁体Sr1-xCaxRuO3系列的磁性

固相反应法制备了Sr1-xCaxRuO3系列. PPMS测量了样品的零场冷却和加场冷却磁化强度和交流磁化率. 居里-外斯定律确定了样品的顺磁居里温度TP. 结果表明, 随x的增加, TP减小. 当x≤0.6时TP大于零; 当x>0.6时TP小于零. 利用交流磁化率随温度变化的关系确定样品的铁磁居里温度TC, 随x的增加TC减小. 当x=0.8时TC降至4 K; 而当x=1.0时, 即使温度降到1.7 K, 也未出现磁有序.     

高温超导体中磁通涡旋的量子隧道效应——TIBaCaCuO化合物磁弛豫…

本报道了ＴＩＢＡＣａＣｕＯ超导体（２２１２，２２２３单相，多晶及薄膜材料）中磁弛豫现象的实验结果，从实验上证实了能量运动由热激活到非热激活机制的转变，实验中得到与温度无关的磁弛豫速率与由通量运动量子隧道效应理论计算结果相一致，同时讨论了各向异性和磁场对磁通的量子漂移速率的影响。