从极化团簇的随机涨落出发,利用维纳过程模型,推导了铁电体中极化长程涨落的弛豫规律以及光强自相关函数所可能的表现形式.阐述了微观极化团簇的弛豫过程与宏观测量弛豫规律之间的联系.通过对原有氦氖激光光子关联谱实验装置进行改进,...从极化团簇的随机涨落出发,利用维纳过程模型,推导了铁电体中极化长程涨落的弛豫规律以及光强自相关函数所可能的表现形式.阐述了微观极化团簇的弛豫过程与宏观测量弛豫规律之间的联系.通过对原有氦氖激光光子关联谱实验装置进行改进,观测了BaTiO3和0.71Pb(Mg1/3Nb2/3)O3-0.29Pb Ti O3单晶中极化团簇长程涨落在居里点和立方到四方相变点附近的弛豫过程.在BaTiO3中发现极化团簇长程涨落在居里点之上4 K存在双弛豫现象,此现象与其有序无序相变机理相联系.在Pb(Mg1/3Nb2/3)O3-0.29PbTiO3中发现极化团簇长程涨落在相变点两侧都存在双弛豫现象.利用推导的理论结果很好地拟合了实验结果并提取了极化团簇长程涨落的弛豫时间.两种样品中极化团簇长程涨落的弛豫时间都在相变点出现突变,并呈现临界慢化现象.展开更多
Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67（Ca0.65Ba0.35）0.33MnO3 and xPd-La0.67（Ca0.65Ba0.35）0.33MnO3 （abbreviated by xAg-LCBMO and xPd-LCBMO） composites. Both Pd a...Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67（Ca0.65Ba0.35）0.33MnO3 and xPd-La0.67（Ca0.65Ba0.35）0.33MnO3 （abbreviated by xAg-LCBMO and xPd-LCBMO） composites. Both Pd and Ag addition induce a decrease in resistivity and an increase in temperature at which the resistivity reaches its maximum. This is mainly due to the improvement of grain boundaries caused by the segregation of good conductive metal grains on the grain boundaries/surfaces. In addition, both Pd and Ag addition induce a large enhancement of room temperature magnetoresistance （RTMR）. Note that 27% molar ratio of Ag addition induces a large RTMR of about 70%, about ten times larger than pure LCBMO, whereas 27% molar ratio Pd addition brings a much larger RTMR of about 170%. The large enhancements of MR can be attributed to the decrease in resistivity of the samples caused by the good conductive metal. On the other hand, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries plays a very im-portant role in the increase in MR, which induces a large number of spin clusters in Pd-added samples.展开更多
文摘从极化团簇的随机涨落出发,利用维纳过程模型,推导了铁电体中极化长程涨落的弛豫规律以及光强自相关函数所可能的表现形式.阐述了微观极化团簇的弛豫过程与宏观测量弛豫规律之间的联系.通过对原有氦氖激光光子关联谱实验装置进行改进,观测了BaTiO3和0.71Pb(Mg1/3Nb2/3)O3-0.29Pb Ti O3单晶中极化团簇长程涨落在居里点和立方到四方相变点附近的弛豫过程.在BaTiO3中发现极化团簇长程涨落在居里点之上4 K存在双弛豫现象,此现象与其有序无序相变机理相联系.在Pb(Mg1/3Nb2/3)O3-0.29PbTiO3中发现极化团簇长程涨落在相变点两侧都存在双弛豫现象.利用推导的理论结果很好地拟合了实验结果并提取了极化团簇长程涨落的弛豫时间.两种样品中极化团簇长程涨落的弛豫时间都在相变点出现突变,并呈现临界慢化现象.
文摘Electrical properties and magnetoresistance have been studied in two series of xAg-La0.67（Ca0.65Ba0.35）0.33MnO3 and xPd-La0.67（Ca0.65Ba0.35）0.33MnO3 （abbreviated by xAg-LCBMO and xPd-LCBMO） composites. Both Pd and Ag addition induce a decrease in resistivity and an increase in temperature at which the resistivity reaches its maximum. This is mainly due to the improvement of grain boundaries caused by the segregation of good conductive metal grains on the grain boundaries/surfaces. In addition, both Pd and Ag addition induce a large enhancement of room temperature magnetoresistance （RTMR）. Note that 27% molar ratio of Ag addition induces a large RTMR of about 70%, about ten times larger than pure LCBMO, whereas 27% molar ratio Pd addition brings a much larger RTMR of about 170%. The large enhancements of MR can be attributed to the decrease in resistivity of the samples caused by the good conductive metal. On the other hand, the polarization of Pd atoms near the Mn ions on the grain surfaces/boundaries plays a very im-portant role in the increase in MR, which induces a large number of spin clusters in Pd-added samples.
