Magnetoresistance effects of La0.7M0.3MnO3−δ far below the Curie temperature (M=Ca, Pb)
Magnetoresistance effects of La0.7M0.3MnO3−δ far below the Curie temperature (M=Ca, Pb)
复制标题
远低于居里温度的La0.7M0.3MnO3−δ的磁阻效应（M=Ca，Pb）
DOI：
10.1063/1.367728
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
L. Schultz
中科院分区：
文献类型：
--
作者：
K. Dörr;K. Müller;E. Vlakhov;R. Chakalov;R. Chakalova;K. Nenkov;A. Handstein;B. Holzapfel;L. Schultz
采用脉冲激光沉积和磁控溅射分别制备了La0.7Pb0.3MnO3−δ (LPMO)和La0.7Ca0.3MnO3−δ (LCMO)单晶和无织型多晶薄膜。在规定的氧压下，通过热处理控制样品的氧缺乏度δ。当δ≈0时，多晶和单晶薄膜均为铁磁性金属，居里温度Tc为220 ~ 270 K。在温度T≪Tc时，多晶LCMO薄膜在温度T=20、77和180 K时的磁阻比（MR）分别为- 30%、- 20%和- 8%，磁场强度为1.5 kOe。在20k， 200oe左右，场灵敏度高达- 0.5% (Oe)−1。这种现象的可能机制是自旋极化穿过晶界的隧穿。对于单晶薄膜，δ从0到约0.1的变化与掺杂水平x从0.3到0.1的变化具有相似的效果，即从铁磁性金属到铁磁性绝缘体的转变。
Single-crystalline and nontextured polycrystalline thin films of La0.7Pb0.3MnO3−δ (LPMO) and La0.7Ca0.3MnO3−δ (LCMO) have been prepared by pulsed laser deposition and by magnetron sputtering, respectively. The oxygen deficiency δ of the samples was controlled by heat treatments under defined oxygen pressure. For δ≈0, the polycrystalline as well as the single-crystalline films are ferromagnetic metals with Curie temperatures Tc of 220–270 K. At low temperatures T≪Tc, the polycrystalline LCMO films show a negative magnetoresistance ratio (MR) at T=20, 77, and 180 K of −30%, −20%, and −8%, respectively, for a field of 1.5 kOe. At 20 K, around 200 Oe, the field sensitivity is as high as −0.5% (Oe)−1. A possible mechanism for this phenomenon is the spin-polarized tunneling through grain boundaries. For the single-crystalline films, the change of δ from 0 to about 0.1 has a similar effect as changing the doping level x from 0.3 to 0.1, namely, a transition from a ferromagnetic metal to a ferromagnetic insulator...