ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
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(approximate)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(very-much-less-than)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. By variation of δ, the low-temperature resistivity of these samples can be controlled within many orders of magnitude. The negative MR of oxygen-deficient single-crystalline LPMO and LCMO films was found to be as large as −20% at T=0.2Tc. © 1998 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.367728
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