Growth and giant magnetoresistance properties of La-deficient LaxMnO3−δ (0.67≤x≤1) films

Abstract

Epitaxial thin films of lanthanum-deficient LaxMnO3−δ (0.67≤x≤1) have been grown on (100) SrTiO3 substrates by pulsed laser deposition. The as-deposited films exhibit a ferromagnetic transition at temperatures ranging from 115 to 240 K, with the transition temperature (Tc) increasing with higher La deficiency. A sharp drop in resistivity and negative magnetoresistance is observed close to Tc, a behavior similar to that observed in divalent substituted La1−xMxMnO3−δ (M=Ba, Sr, Ca, Pb) films. Postannealing the films in O2 reduces the resistivity and raises the Tc to values close to room temperature. A magnetoresistance value of 130% (Δρ/ρH) has been obtained at 300 K at 4 T for a post-annealed film with x=0.75.

Intrinsic insulating ferromagnetism in manganese oxide thin films

“…The unexpected ferromagnetism was considered to be extrinsic and deficiency of La [10,14] was suggested as a possible explanation to it. However, it is not consistent with the fact that FM phase in the LMO thin films with cation deficiency tends to be metallic [7,15,16]. Previous models [17,18] and recent first-principles studies [19,20] on LMO thin films predicted the metallic FM phase, instead of the experimentally observed insulating FM phase.…”

“…Since the Based on the established orbital order, the magnetic interactions among the Mn atoms in the insulating P21/n FM phase can be deduced according to the Goodenough-Kanamori rules [21]. As a result of the three-dimensionally , higher than experimentally measured ones [7,11] ranging from 115K to 240K. A possible explanation to this discrepancy is that the epitaxial strain is gradually relaxed from the substrate to the film surface, thus the FM phase locates just near the strained film-substrate interface while the bulk-like A-AFM phase dominates at the film surface, similar to the case of the strain-induced ferromagnetism in the antiferromagnetic LuMnO 3 thin film [35].…”

“…Experiments discovered a surprising insulating ferromagnetic phase in LMO thin films epitaxially grown on the square-lattice SrTiO 3 (STO) substrate [2,[7][8][9][10][11][12][13]. The origin of this puzzling insulating FM phase is unclear.…”

Comment on “Ferromagnetism at room temperature in La0.8Ca0.2MnO3 thin films” [Appl. Phys. Lett. 74, 1886 (1999)]

“…We feel that one of the possibilities for a higher T p and T c for xϭ0. 2 8 It has been shown that T c of the as-deposited thin film sample of La 0.75 MnO 3 has increased from ϳ240 to ϳ300 K after annealing in oxygen and the resistivity of La 1Ϫx MnO 3 decreases with increasing x. Therefore, the high T c and T p and the lower resistivity of the thin film sample, 1 compared to that of the bulk, are in accordance with the La deficiency of the film.…”

Transmission electron microscopy study of epitaxial La0.8MnO3thin films on SrTiO3

“…A magnetoresistance of 85% under 6T was obtained in La 0.7 MnO 3 films on LaAlO 3 prepared by pulsed laser deposition (PLD) with a substrate temperature of 993K [7]. Gupta et al [8] reported a magnetoresistance of 55% under 4T in La 0.75 MnO 3 films grown by PLD on SrTiO 3 at 973K.…”