Anomalous Magnetoresistance Effect in Strained Manganite Ultrathin Films
- PDF / 490,807 Bytes
- 10 Pages / 418.68 x 637.2 pts Page_size
- 89 Downloads / 229 Views
ABSTRACT Magnetotransport properties of strained epitaxial Pr 2/ 3 Srl/ 3 MnO2 (PSMO) ultrathin films have been studied. The strains are controlled by growing PSMO films on different lattice-mismatched substrates which impose biaxial compressive-, tensile-, and very little strain in the films, respectively. Distinctive magnetoresistance effects in low magnetic field (LFMR) have been observed in films with different types of strain. The films with compressive strain show very large negative LFMR (> 1000 % at 2500 Oe) and significant magnetoresistance hysteresis when a magnetic field is applied perpendicular to the film plane. In a parallel field, the LFMR is much smaller with almost no hysteresis. In contrast, the tensile-strained ultrathin films show positive LFMR at low temperatures in a perpendicular field and a negative LFMR in a parallel field. In comparison, the almost strain-free ultrathin films show very small LFMR (< 2 %) as in single crystal samples at similar temperatures and magnetic fields. In the compressive-strained samples, the large LFMR decreases rapidly with increasing film thickness. These results are interpreted based on spin dependent scattering
at the domain walls and domain-rotation.
INTRODUCTION Recently, the doped manganese oxides have been the focus of intensive research due to the colossal magnetoresistance (CMR) effect observed in the system [1, 2, 3, 4]. The manganites are perovskite oxides with a composition Re,-.AMnO 3 , where Re is a rare earth and A is a divalent alkali element. The material is ferromagnetic in the doping range of about x 0.2-0.5, and the CMR effect occurs near the ferromagnetic transition temperature T,. The ferromagnetic properties of manganites are traditionally interpreted by the double exchange picture between Mn 3 + and Mn 4 + [5, 6, 7] and are very sensitive to the lattice distortions, such as the external hydrostatic pressure in the bulk samples [8, 9, 10], the "internal pressure" due to rare earth substitution [11, 12]. It is proposed theoretically that the CMR effect is related to the localization effect due to a strong dynamical electron-lattice coupling involving
185 Mat. Res. Soc. Symp. Proc. Vol. 602 © 2000 Materials Research Society
Jahn-Teller vibration mode [13]. The Jahn-Teller mode is associated with a uniaxial volumepreserving lattice distortion. Therefore, the uniaxial lattice strain in thin films has been shown to affect the magnetotransport properties [14, 15, 16, 17]. Strain also affects the magnetic anisotropy of the thin film samples. In manganites, experiments show that the intrinsic magnetocrystalline anisotropy is very weak [18]. There is essentially no MR anisotropy in single crystals. In thin films, on the other hand, the strain-induced anisotropy has been found to play a dominant role in the magnetic anisotropy energy [19, 20]. Magnetic anisotropy can have dramatic influence on the MR properties, in particular the low field MR (LFMR) effect[21, 22]. Since most proposed applications of the CMR materials involve thin films, it is v
Data Loading...
