Carrier transport spin–orbit dynamics in surface enhanced Raman shift of perovskite films
Introduction
LSMnO3 colossal magnetoresistance oxides are one of the most promising materials for the fabrication of optoelectronic devices. Raman scattering is known to be a powerful technique to research the dynamics caused by phonons. The doped manganese oxides La0.7Sr0.3MnO3 (LSMO) displays competition coupling of spins, charge, orbital, and lattice order. ZnO is a most popular semiconductor material with a wide band gap (3.37 ev) and large exciton binding energy (60 mev) which potentially possesses the characteristics of ultraviolet wavelength, high efficiency, lower power, light emitting and laser diodes. The heterojunction ZnO/La0.7Sr0.3MnO3+σ nanostructure is good candidate for fabrication of nanometer-sized optoelectronic devices. It is expected that structural changes and spin–orbital magnetic order will influence the phonon spectra. The doped strontium La0.7Sr0.3MnO3+σ and ZnO junctions with carrier transfer have electron spin order, orbital order, and lattice field properties, and exhibit photoinduced resistance and colossal magnetoresistance (CMR) effect [1], [2], [4]. So far, many groups have reported the growth of two dimensional heterojunction nanostructures using different methods [3], [5]. Pabst focused on optoelectronic mechanisms, which led to the large leakage current in high quality BFO thin films to integrate BFO into functional microelectronic devices [12]. It is reported that transport behavior accompanying domain switching can be obtained in La0.1Bi0.9FeO3/La0.7Sr0.3MnO3 [15]. Arindam used nonequilibrium magnetotransport spectroscopy to explore spin polarization at low temperature and a strong sensitivity of such polarization to magnetic fields [13]. Although Raman spectra of other perovskites have been reported, there are no information on the lattice dyanamics in heterojunction films as well as to analyze more specific aspects of phonon-electron interaction and isotopic effects.
Previous studies of hexagonal manganites have been focus on bulk crystals. With the trend in developing low dimension and more heterojunction device, or nanostructures have become desirable. However, in oxide thin film and doped defects, the thin film with oxygen defects and distortion LSMO heterojunction or nanostructures seem to be essential for their potential applications [6], [7]. The LSMO has a rhombohedral structure with the R3C space group with O(1) in-plane and O(2) apical oxygen sites as some high-Tc cuprates. The LaO2 and SrO2 planes are stacked along a–b axis and separated by the MnO2 planes as the result of a ferromagnetic-orbital ordering of orbital and C-type antiferromagnetic (AF) spin ordering below T = 117–127 k. Ferroelectric ZnO contains transition metal ions with unpaired d electrons. The presence of the d electrons can result in a relatively small gap and give rise to a concentration of charged impurities and defects [14]. The question is whether the spin–orbital degrees of freedom are a relevant parameter to describe the properties of ZnO/La0.7Sr0.3MnO3 characteristics.
In this letters, we reported Raman scattering and partial wave state density studies of ZnO/La0.7Sr0.3MnO3+σ/LaAlO heterojunction with different thickness nanostructure to investigate spin–orbital dynamics of phase transition from insulator to metal. We prepared multi-crystal LSMO/ZnO to introduce MR and carrier injection. A temperature dependence of positive magnetoresistance was observed in this junction that has some special properties of ferromagnetic semiconductor [8], [9], multilevel resistive switching [10], positive colossal magnetoresistance [11], [12], colossal electroresistance [13], manganite tunnel junctions [14], high magnetic sensitivity [15] and ultraviolet fast-response [15].
Section snippets
Experiments
The spin polarization transport of double exchange mechanics are observed in metal insulate transition, which the substitution of divalent alkaline earth element leads to the mixed valence state of Mn:Mn3+t2g 3d and Mn4+t2g 3d. A temperature driven orbital occupation of diluted is in the background of crystal field . It is so called spin coupling strongly to the lattice. Moreover, the Mn3+–O2−–Mn4+ coupling produces ferromagnetic strong correlation through the charge hopping
Results and discussion
The XRD image indicated that the La0.7Sr0.3MnO3+σ (100) and (200) diffraction peaks occurred at 2θ = 23° and 2θ = 47°, while the ZnO (100) (002) (101) (102) (110) (103) (200) diffraction peak occurred at 2θ = 31.59°,2θ = 34.37°, 2θ = 36.09°, 2θ = 47.3°,2θ = 56.4°, 2θ = 62.78° and 2θ = 66.15°. No macroscopic second phase where the major peaks of the impurity phases have been previously observed is visible. Besides the spectrum peak showed orientation of LSMO crystal plane, the diffraction peak
Conclusions
In summary, by using epitaxial LSMO/ZnO films, we have present Raman scattering spectrum and energy band density structure on the single and multilayer junction LSMO of orbit-spin couple to the lattice. We study the carrier transport spin-orbit dynamic made by the lattice distortion in ZnO/LaSrMnO and Jahn-Teller distortion of MnO6 octahedron. The spin–orbital dynamics indicates that orbital coupling is origin of lattice anomalic. We emphasize the carrier transport spin–orbit dynamic made by
Acknowledgments
Supported by the National Natural Science Foundation of China under Grant No 61574115.
References (15)
- et al.
Phys. Rep.
(2001) - et al.
Solid State Commun.
(1996) - et al.
J. Appl. Phys.
(1994) - et al.
Phys. Rev. Lett.
(1993) Phys. Rev.
(1951)- et al.
Optoelectron. Adv. Materials-Rapid Commun.
(2010) - et al.
Science
(1994)