Laterally mesoscopic-patterned La0.67Sr0.33MnO3 thin film by pulsed laser deposition on anodic aluminum oxide template
Introduction
As a strong potential candidate for spintronics devices, manganites with a perovskite structure have been extensively studied in bulk and thin film forms [1], [2]. Very recent investigations on manganites with even lower dimension show larger low field magnetoresistance (LFMR) value in La0.67Sr0.33MnO3 (LSMO) nanoconstrictions [3], [4] and nanowires [5], novel resistance steps in LSMO nanoconstriction array [6], negative differential resistance in Pr0.65(Ca0.75Sr0.25)0.35MnO3 of mesoscopic pattern [7], all of which are different from those in bulk and continuous thin films. Fabrication of the structures with lateral size of several tens nanometers in a cost-effective way is still a challenge in this field.
Anodic aluminum oxide (AAO), hexagonally ordered arrays of nanopores formed by anodization of aluminum in an appropriate acid solution, has been demonstrated to be very versatile in fabricating nanoscale structures. It has been widely used as template to fabricate nanowires of different materials [8], [9], [10], as mask for pulse laser deposition to fabricate nanodots [11], as a pattern-transfer nanomask [12] and as template to prepare molds with nanoscale features [13]. In this work, by employing AAO as the substrate for pulsed laser deposition (PLD), we demonstrate a simple way to fabricate mesoscopic-patterned LSMO film with the lateral size down to several tens nanometers. This laterally mesoscopic-patterned LSMO film exhibits typical low field magnetoresistance with the coercive field relatively larger compared with the continuous polycrystalline film on Al2O3 substrate.
Section snippets
Experimental
The fabrication procedure, including the preparation of AAO template with the bottom barrier removed, attaching the AAO template onto a Si substrate and the thin film deposition on AAO surface, is presented schematically in Fig. 1. The AAO template was prepared as follows: first, a pure aluminum foil (99.5%), annealed at 500 °C for 5 h, was electropolished in a solution of perchloric acid and ethanol (1:4 vol.%). Then, it was anodized at a constant voltage of 40 V in a 0.3 M oxalic acid
Results and discussion
The transport properties of the patterned LSMO thin film and the reference sample were measured using standard four point probe technique. Fig. 3 shows the temperature dependence of resistance (RT curves) of the films on AAO template and on continuous Al2O3 substrate with no magnetic field applied. It can be seen that the two curves are qualitatively the same despite the apparent differences in their resistance value: there exists a metal to insulator transition temperature Tp (208 K for the
Conclusions
In summary, the mesh-like patterned half-metallic LSMO film was fabricated by pulsed laser deposition on AAO template with lateral size down to 30–50 nm. This laterally mesoscopic-patterned LSMO film exhibits typical low field magnetoresistance with the coercive field relatively larger compared with the continuous polycrystalline film on Al2O3 substrate. This work provides a cost-effective method to fabricate mesoscopic-pattern film with the lateral size down to several tens nanometers.
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2012, Applied Surface ScienceCitation Excerpt :The perovskite manganites R1−xAxMnO3 (R = trivalent rare-earth ions, A = divalent alkaline earth ions) have attracted scientific community for last many decades [1–3]. The lanthanum based perovskites have different physical properties and potential applications in various fields, such as fuel cells [4,5], magnetic refrigeration [6,7], sensors [8,9], infrared devices [10], spintronics [11,12], and CMR [13,14]. LSMO possesses the value of Curie temperature around room temperature and carrier density (1021 to 1022 cm−3) with a high spin polarization of charge carriers among perovskite-structured manganite systems that makes it very promising in room-temperature applications [15,16].
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