Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

ELECTRICAL RESISTANCE AND MAGNETORESISTANCE OF HIGHLY ORIENTED AND POLYCRYSTALLINE La_0.67Sr_0.33MnO₃/MgO(001) THIN FILMS
Bonifacas Vengalis^a, Irina Černiukė^a, Andrius Maneikis^a, Antanas Kleopas Oginskis^a, and Gražina Grigaliūnaitė-Vonsevičienė^b
^aCenter for Physical Sciences and Technology, A. Goštauto 11, LT-01108 Vilnius, Lithuania
E-mail: veng@pfi.lt
^bVilnius Gediminas Technical University, Saulėtekio 11, LT-10223 Vilnius, Lithuania

Received 6 February 2015; revised 28 February 2015; accepted 15 June 2015

La_0.67Sr_0.33MnO₃ thin films exhibiting a highly (001)-plane oriented and polycrystalline structure with a variable amount of (011)-textured crystallites have been grown in situ by RF magnetron sputtering on crystalline MgO(001) substrates by changing deposition temperature from 550 to 800 °C. Competing contribution of grains and grain boundaries to resistivity and magnetoresistance of the films has been investigated at T = (78–330) K. A model based on two parallel channels of current flow across grain boundaries has been applied to explain coexistence of low (LFMR) and high field (HFMR) magnetoresistance effects in the polycrystalline films at low temperatures. The LFMR effect has been understood assuming tunnelling of spin-polarized carriers via magnetic field-driven tunnelling barriers formed naturally between neighbouring misoriented grains. Meanwhile, the HFMR phenomenon has been associated with magnetic field-dependent hopping of carriers via the intergrain regions with reduced carrier density. Importance of the phase separation phenomenon on possible inhomogeneity of the material at grain boundaries has been discussed.

Keywords: LSMO thin films, grain boundaries, electrical resistivity, low field magnetoresistance
PACS: 73.43 Qt, 73.61-r, 71.30.+h, 75.70

PLONŲJŲ TEKSTŪRUOTŲ IR POLIKRISTALINIŲ La_0,67Sr_0,33MnO₃/MgO(001) SLUOKSNIŲ ELEKTRINĖ VARŽA IR MAGNETOVARŽA

Bonifacas Vengalis^a, Irina Černiukė^a, Andrius Maneikis^a, Antanas Kleopas Oginskis^a, Gražina Grigaliūnaitė-Vonsevičienė^b
^aFizinių ir technologijos mokslų centras, Vilnius, Lietuva
^bVilniaus Gedimino technikos universitetas, Vilnius, Lietuva

Plonieji (100) plokštumoje orientuoti La_0,67Sr_0,33MnO₃ (LSMO) sluoksniai, taip pat polikristaliniai LSMO sluoksniai su papildomais (110) plokštumoje orientuotais kristalitais buvo užauginti magnetroninio dulkinimo būdu keičiant kristalinių MgO(100) padėklų temperatūrą nuo 550 iki 800 °C. Ištirta kristalinių grūdų ir tarpkristalinių sričių įtaka sluoksnių elektrinei varžai ir magnetovaržai 78–330 K temperatūrų ruože. Tarpkristalinių ribų magnetovaržai silpnuose (LFMR) ir stipriuose (HFMR) magnetiniuose laukuose paaiškinti buvo pasitelktas dviejų lygiagrečių elektrai laidžių kanalų modelis. LFMR reiškinys polikristaliniuose LSMO sluoksniuose paaiškintas krūvininkų su orientuotais sukiniais tuneliavimu per magnetiniu lauku valdomą tunelinį barjerą, susidarantį technologinio proceso metu tarp gretimų skirtingai orientuotų kristalinių grūdų. Žymi polikristalinių sluoksnių magnetovarža, esant žemoms temperatūroms ir stipriems magnetiniams laukams, buvo susieta su šuoliniu krūvininkų transportu per tarpkristalines sritis, pasižyminčias sumažinta krūvininkų koncentracija. Aptarta galima fazinio išsisluoksniavimo reiškinio įtaka nevienalytei tarpgrūdinei terpei susidaryti tiriamuosiuose polikristaliniuose LSMO sluoksniuose.

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