Nb^(5+)的掺杂引起La_(0.67)Sr_(0.33)MnO_3增强的磁电阻效应

Enhancements of magnetoresistance in Nb^(5+)-doped La_(0.67)Sr_(0.33)MnO_3

将Nb2O5掺杂到用溶胶-凝胶法制备的La0.67Sr0.33MnO3(LSMO)微粉中,XRD测量结果表明所有样品均为单相菱面结构。随着Nb5+掺杂量的增加,材料电阻率发生显著变化。在x=0.06的掺杂样品中得到最高为1110Ω.cm电阻率(x是掺入的Nb离子与母体材料的摩尔比),比LSMO高5个数量级,这是由于晶界处以及颗粒内部增加的自旋相关的散射和隧穿效应所致。Nb5+离子的掺杂使样品的低场磁电阻(LFMR)和高场磁电阻(HFMR)效应都有所增强。77K下,0.1和1T磁场下在x=0.07样品中分别得到25%和42%的磁电阻效应,分别是LSMO样品的2倍和1.7倍。室温下x=0.03样品的磁电阻最大,为7%。其中,LFMR来源于颗粒晶界处电子的自旋相关隧穿及散射作用,而HFMR来源于表面层的自旋非共线结构。

The samples were prepared by doping Nb2O5 into the La0.67 Sr0.33 MnO3 powder, which is synthesized by the sol-gel method. The XRD result indicates that all samples can be indexed based on the rhombohedral structure with single phase. The resistivities of the samples are influenced remarkably by Nb^5＋ addition. There is a maximum resistivity ρ for the sample with x=0.06 （x is the molar ratio of the Nb ions to LSMO）, which is higher than that for LSMO by five orders of magnitude. It is due to the enhancement of spin dependent and independent scattering and tunneling effects on the interfaces of grain boundaries and inside the grains. Enhancements of the low-field magnetoresistance （LFMR） and high-field magnetoresistance （HFMR） were observed. The maximum MR ratios at 77K with H=1T and H=0.1T are 42% and 25% for the 0.07molar ratio doped sample, which are 2 times and 1.7 times as large as that for LSMO, respectively. A MR effect up to 7% was also found for the sample with x= 0.03 at room temperature. The spin dependent tunneling and scattering at the interfaces of grain boundaries are responsible for the LFMR while the HFMR originates from a noncollinear spin structure in the surface layer.