The long-term stability of electrical resistance and magnetoresistance in nanostructured La_1-xSr_xMnO₃ (x = 0.17) manganite thin films grown on lucalox (Al₂O₃ + MgO) substrate by the MOCVD method was investigated. It was found that the storage of up to 3 months of the free surfaces of these films in normal atmosphere (air) conditions increases their resistivity by almost two times, while the annealing of the films in an Ar atmosphere at 450 °C decreases their resistivity only by 15%. It was concluded that the final increase of resistivity is determined by a long-term relaxation of the grain boundaries in the nanostructured films. The magnetoresistance of the films does not change significantly, which produces an advantage for magnetic field sensor applications. The passive protective coating of the free surfaces of the films stabilizes their electrical and magnetic properties. The results were analysed using various electron scattering mechanisms when the films were in a ferromagnetic state, and the Mott’s variable range hopping model when they were in a paramagnetic insulating state.

Keywords: manganites, electrical resistivity, colossal magnetoresistance, polycrystalline thin films, magnetic field sensors, ageing effects
PACS: 75.47.Gk, 72.20.My, 85.75.Ss

SENĖJIMO ĮTAKA NANOSTRUKTŪRIZUOTŲ MANGANITŲ SLUOKSNIŲ SAVITAJAI VARŽAI IR MAGNETOVARŽAI
L. Žurauskaitė^a, S. Balevičius^a,b, N. Žurauskienė ^a,b, S. Keršulis^a, V. Stankevič^a,b,
Č. Šimkevičius^a,b, J. Novickij^b, and  S. Tolvaišienė ^b
aFizinių ir technologijos mokslų centro Puslaidininkių fizikos institutas, Vilnius, Lietuva
^bVilniaus Gedimino technikos universitetas, Vilnius, Lietuva

Siekiant panaudoti manganitų sluoksnius įvairių prietaisų kūrimui, labai svarbu, kad jų parametrai ilgą laiką išliktų stabilūs. Ištirta senėjimo įtaka nanostruktūrizuotų La_1-xSr_xMnO₃ (x = 0,17) sluoksnių, užaugintų MOCVD metodu ant polikoro (Al₂O₃ + MgO) padėklo, savitajai varžai ir magnetovaržai. Nustatyta, kad sluoksniui esant (keletą mėn.) normalioje atmosferoje (ore), beveik du kartus padidėja jo varža (kaitinant 420 °C temperatūroje), o atmosferoje ji sumažėja 15 %. Padaryta išvada, kad sluoksnio savitosios varžos ilgalaikius pokyčius lemia tarpkristalitinių sričių relaksacija, todėl atsiranda papildomi defektai ir vakansijos. Sluoksnių magnetovarža mažai pakinta. Pasyvuojanti paviršių medžiaga stabilizuoja sluoksnių elektrines ir magnetines savybes. Gauti rezultatai išanalizuoti panaudojant įvairius elektronų sklaidos aprašymus, esant sluoksniui feromagnetinėje būsenoje bei Mott’o šuolinio laidumo modeliui paramagnetinėje būsenoje.

References / Nuorodos

[1] C. Israel, M.J. Calderón, and N.D. Mathur, The current spin on manganites, Mater. Today 10, 24–32 (2007),
http://dx.doi.org/10.1016/S1369-7021(07)70242-0
[2] J.E. Evetts, M.G. Blamire, N.D. Mathur, S. P. Isaac, B.-S. Teo, L.F. Cohen, and J.L. Macmanus-Driscoll, Defect-induced spin disorder and magnetoresistance in single-crystal and polycrystal rare-earth manganite thin films, Phil. Trans. R. Soc. Lond. A 356, 1593–1615 (1998),
http://dx.doi.org/10.1098/rsta.1998.0237
[3] M. Schneider, O. Liebfried, V. Stankevic, S. Balevicius, and N. Zurauskiene, Magnetic diffusion in railguns: Measurements using CMR-based sensors, IEEE Trans. Magn. 45(1), 430–435 (2009),
http://dx.doi.org/10.1109/TMAG.2008.2008539
[4] N. Žurauskienė, S. Balevičius, V. Stankevič, S. Keršulis, M. Schneider, O. Liebfried, V. Plaušinaitienė, and A. Abrutis, B-scalar sensor using CMR effect in thin polycrystalline manganite films, IEEE Trans. Plasma Sci. 39(1), 411–416 (2011),
http://dx.doi.org/10.1109/TPS.2010.2064338
[5] P.K. Siwach, H.K. Singh, and O.N. Srivastava, Low field magnetotransport in manganites,
http://arxiv.org/ftp/cond-mat/papers/0506/0506239.pdf
[6] K.-H. Dahmen and  M.W. Carris, MOCVD of HTS and GMR perovskites by aerosol and liquid delivery MOCVD, J. Alloy Compd. 251, 270–277 (1997),
http://dx.doi.org/10.1016/S0925-8388(96)02684-9
[7] V.G. Prokhorov, G.G. Kaminsky, and V.A. Komashko, Y.P. Lee, and J.S. Park, Oxygen-deficiency-activated phase transition in a long-aged La _0.8Ca_0.2MnO₃ film, Appl. Phys. Lett. 80(15), 2707–2709 (2002),
http://dx.doi.org/10.1063/1.1470244
[8] J.M.D. Coey, M. Viret, and S. von Molnár, Mixed-valence manganites, Adv. Phys. 48(2), 167–293 (1999),
http://dx.doi.org/10.1080/000187399243455
[9] M. Egilmez, M.M. Saber, M. Abdelhadi, K.H. Chow, and J. Jung, Anomalous aging and strain induced time dependent phenomena in ultra-thin La_0.65 Ca_0.35MnO₃ films, Phys. Lett. A 375, 4049–4052 (2011),
http://dx.doi.org/10.1016/j.physleta.2011.08.067
[10] N. Kozlova, K. Dörr, D. Eckert, A. Handstein, Y. Skourski, T. Walter, K.-H. Müller, and L. Schultz, Slow relaxation of grain boundary resistance in a ferromagnetic manganite, J. Appl. Phys. 93, 8325–8327 (2003),
http://dx.doi.org/10.1063/1.1544455
[11] A. Abrutis, V. Plausinaitiene, V. Kubilius, A. Teiserskis, Z. Saltyte, R. Butkute, and J.P. Senateur, Magnetoresistant La_1-xSr _xMnO₃ films by pulsed injection MOCVD: effect of deposition conditions, substrate material and film thickness, Thin Solid Films 413, 32–41 (2002),
http://dx.doi.org/10.1016/S0040-6090(02)00352-8
[12] S.W. Yia, G. Pan, Z.L. Cai, Y. Wang, and J.R. Reimers, The manganite−water interface, J. Phys. Chem. C 111, 10427–10437 (2007),
http://dx.doi.org/10.1021/jp068842t
[13] A. Urushibara, Y. Moritomo, T. Arima, A. Asamitsu, G. Kido, and Y. Tokura, Insulator-metal transition and giant magnetoresistance in La_{1- x}Sr_xMnO₃, Phys. Rev. B 51(20) 14103–14109 (1995),
http://dx.doi.org/10.1103/PhysRevB.51.14103
[14] S. Hcini, S. Zemni, A. Triki, H. Rahmouni, and M. Boudard, Size mismatch, grain boundary and bandwidth effects on structural, magnetic and electrical properties of Pr_0.67Ba_0.33MnO₃ and Pr _0.67Sr_0.33MnO₃, J. Alloy Compd. 509, 1394–1400 (2011),
http://dx.doi.org/10.1016/j.jallcom.2010.10.190
[15] D. Varshney and N. Dodiya, Electrical resistivity of the hole doped La_0.8Sr_0.2MnO₃ manganites: Role of electron-electron/phonon/magnon interactions, Matter. Chem. Phys. 129 , 896–904 (2011),
http://dx.doi.org/10.1016/j.matchemphys.2011.05.034
[16] M. Viret, L. Ranno, and J.M.D. Coey, Magnetic localization in mixed-valence manganites, Phys. Rev. B 55, 8067–8070 (1997),
http://dx.doi.org/10.1103/PhysRevB.55.8067
[17] S. Lee, H.Y. Hwang, B.I. Shraiman, W.D. Ratcliff II, and S.-W. Cheong, Intergrain magnetoresistance via second-order tunneling in perovskite manganites, Phys. Rev. Lett. 82, 4508–4511 (1999),
http://dx.doi.org/10.1103/PhysRevLett.82.4508
[18] N. Žurauskienė, S. Keršulis, L. Medišauskas, and S. Tolvaišienė, Investigation of magnetoresistance and its anisotropy of thin polycrystalline La_0.83 Sr_0.17MnO₃ films in high pulsed magnetic fields, Acta Phys. Pol. A 119, 186–188 (2011),
http://przyrbwn.icm.edu.pl/APP/ABSTR/119/a119-2-29.html