Cationic Ordering and Microstructural Effects in the Ferromagnetic Perovskite La0.5Ba0.5CoO3: Impact upon Magnetotransport Properties

Collins

Applied Physics Letters

et al. 2010

Giant resistance switching behavior in mixed conductive ͑LaBa͒Co 2 O 5+␦ epitaxial thin film were discovered in high temperature and reducing environments during the reduction and reoxidation process. A reproducible resistance response of over 99% was achieved in the films during a change of 4% H 2 / 96% N 2 to oxygen at temperature range of 400-780°C. The results indicate that at, low oxygen partial pressure, the extension of oxygen deficiency is an essential factor to the high temperature physical properties of ͑LaBa͒Co 2 O 5+␦ and demonstrates its potential application as a chemical sensor device for reducing environments at high temperature. © 2010 American Institute of Physics. ͓doi:10.1063/1.3484964͔Cobalt based perovskite oxides have received increasing attention in the past decade due to their high mixed ionicelectronic conductivity in chemical sensor and green energy device development.1,2 Recent studies indicate that oxygen deficient doped double perovskite cobaltates ͑LnBa͒Co 2 O 5+␦ ͑Ln= La, Pr, Gd͒ have excellent mixed ionic-electronic conductivity with a fast surface exchange coefficient. [3][4][5] In this family of compounds, the A-site cationic ordered arrangement is favored due to the large difference in Ba 2+ and rare earth ionic radii, except ͑LaBa͒Co 2 O 5+␦ ͑LBCO͒. In LBCO, the doped bivalent Ba 2+ is not only inducing plenty of oxygen deficiency but also structurally providing the capability to achieve the smallest oxygen deficiency in this family of compounds due to the very similar ionic radii between Ba 2+ and La 3+ . Therefore, LBCO provides a unique platform with the geometrical stabilized perovskite phase and a wide range of oxygen deficiency, which enables one to study the electrical conductivity, defect structures and stability at high temperature over a wide range of oxygen partial pressure.Up to now, studies on LBCO are only limited to the bulk polycrystalline samples for low temperature transport and magnetic properties.6-8 The high temperature physical properties of LBCO are rarely studied due to the structure failure of the bulk material in a reducing environment. Recently, we have fabricated epitaxial single crystalline LBCO thin films on ͑001͒ LaAlO 3 ͑LAO͒, enabling one to systematically study the electrical transport properties of LBCO under various environments. A reproducibly dramatic resistance change is observed as the LBCO film is exposed to oxidizing and reducing environment over a wide range of temperature. Especially, it is interesting to note that the re-oxidation of the LBCO film has a very short response time, suggesting that an exceedingly fast oxygen exchange rate occurs at the film surface.A KrF excimer pulsed laser deposition system with a wavelength of 248 nm was employed to deposit the ͑LaBa͒Co 2 O 5+␦ thin films on ͑001͒ LaAlO 3 substrates. An energy density of 2.0 J / cm 2 and a laser repetition rate of 5 Hz were adopted during film deposition. A high density, single phase, stoichiometric ͑LaBa͒Co 2 O 5+␦ target was purchased from Praxair Inc. The deposit...

mentioning

confidence: 99%

PO 2 dependant resistance switch effect in highly epitaxial (LaBa)Co2O5+δ thin films

Collins

Applied Physics Letters

et al. 2010

“…8,9 Raveau's group systematically studied the fully oxidized nanoscale-ordered LaBaCo 2 O 6 , disordered La 0.5 Ba 0.5 CoO 3 , and the oxygendeficient ordered LaBaCo 2 O 5.5 and concluded that various interesting phenomena in these systems are originated from the locking of magnetic spins in the nanodomain structures. 1,2 To fully understand the physical phenomena in these complex systems, single crystalline materials are becoming critical for tackling these problems. We have fabricated single crystalline highly epitaxial ͑LaBa͒Co 2 O 5.5+␦ thin films and found that the as-grown LBCO thin films have extraordinary sensitivity to reducing-oxidizing environments and the exceedingly fast surface exchange rate at high temperature.…”

mentioning

confidence: 99%

Magnetic and transport properties of epitaxial (LaBa)Co2O5.5+δ thin films on (001) SrTiO3

Applied Physics Letters

Collins

et al. 2010

The (LaBa)Co2O5+δ thin films were grown on (001) SrTiO3 single crystal substrates by using pulsed laser deposition. Microstructure studies from x-ray diffraction and electron microscopy show that the films have good epitaxial quality with a-axis orientation and sharp atomic interface. Transport property and isothermal magnetoresistance measurements have been used to understand the physical properties of the films with anomalous magnetic phenomena and the largest reported magnetoresistance value of 19% at 40 K.

“…However under H = 90 kOe measurement condition the resistivity is increased and these two observed -MR peaks at 15 and 235 K are suppressed to 1.4 and 1%, respectively. The -MR seen under the low temperature region seems to be explained in terms of grain boundary effects [25,[35][36][37]. For x = 0.15 sample, under H = 70 kOe condition, the +MR at room temperature (4.6%) decreases by decreasing temperature and attain -MR crossover at 205 K and at 20 K it shows -MR about 1.3%.…”

Section: Resultsmentioning

confidence: 90%

Syntheses and Magnetic-Properties of Zn-Diluted Sr-Based Perovskite Cobalt Oxides, Sr1−x Zn x CoO3; 0.05≤x≤0.3

Balamurugan

2012

J Supercond Nov Magn

In order to check the solubility of Zn in the (Sr 1−x Zn x )CoO 3 perovskite structure and their research findings, several polycrystalline samples have been prepared under wide extreme synthesis conditions at 6 GPa/1300-1650°C. While 0.05 ≤ x ≤ 0.3 compositions revealed single phased cubic structure materials, x > 0.3 showed multiphased materials for (Sr 1−x Zn x )CoO 3 system. Like other substituted perovskite cobalt oxide systems (Ca, Y, Ho and Ce), the transport properties of the present materials show rather sizable changes with respect to 'x', although there are insignificant variations in lattice parameter and in Curie temperature, T c . All the present samples show soft ferromagnetism with T c in the range of 272-285 K for 0.05 ≤ x ≤ 0.3. The effective paramagnetic moment, P eff determined from the paramagnetic region decreases upon the substitution of Zn for Sr-site. These P eff (3.3-2.8 µ B /Co) values for 0.05 ≤ x ≤ 0.3 compositions seem to suggest that the Co 4+ lie in intermediate spin (IS) state for the present (Sr 1−x Zn x )CoO 3 series, although they are slightly smaller than those expected for IS-Co 4+ ; P eff = 3.87 µ B /Co. The electrical resistivity is found to increase with increase of 'x' for the investigated samples. The temperature and field dependence of both positive and negative magnetoresistance (MR) are noted for the Zn substituted samples. About 5% of -MR is observed for x = 0.05 sample around the transition temperature (280 K) under the field strength difference, H = 90 kOe. The present research findings are compared with our previous results on different perovskite cobalt oxides.