Ageing effects on electrical resistivity and magnetoresistance of nanostructured manganite films

Abstract

The long-term stability of electrical resistance and magnetoresistance in nanostructured La 1-x Sr x MnO 3 (x = 0.17) manganite thin films grown on lucalox (Al 2 O 3 + 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.

Engineering of Functional Manganites Grown by MOCVD for Miniaturized Devices

“…Table 1 summarizes the most significant works reported up to now by relevant world‐class groups working in the field. A vast number of manganites systems have been synthetized, including a huge variety of lanthanum manganites (La 1– y A′ y )MnO 3 : La 1– y Sr y MnO 3 (0 ≤ y ≤ 0.65), La 0.7 Ca 0.3 MnO 3 , La 0.8 Ba 0.2 MnO 3 , La 1– y K y MnO 3 (0.05 ≤ y ≤ 0.4), La 0.82 Na 0.18 MnO 3 ; YMnO 3 , and other lanthanide manganites such as Pr 1– y Ca y MnO 3 (0.05 ≤ y ≤ 0.64), Pr 0.6 Sr 0.4 MnO 3 , LuMnO 3 , ErMnO 3 , DyMnO 3 , HoMnO 3 , TbMnO 3 , and NdMnO 3 …”

“…The grain boundaries density, which generally has a different conductivity mechanism than the grains, may influence the magnetoresistance properties of manganites . Abrutis and co‐workers have extensively studied this effect for La 0.83 Sr 0.17 MnO 3 (LSMO) films deposited on several substrates, i.e., STO, LAO and lucalox (99% Al 2 O 3 + 0.1% MgO) …”

“…The second part of their work consisted in the investigation of the effect of crystallites in thick LSMO films (≈400 nm). Randomly oriented crystallites (≈20 nm) aggregated in larger clusters (≈130 nm) were obtained at 1023 K onto lucalox substrates . The electrical and magnetic properties were investigated in the temperature and field range of 5–315 K and 0–0.8 T, respectively, using the two‐terminal method.…”

Accelerated ageing effects in nanostructured La0.83Sr0.17MnO3 films

“…In this case the stability of the electrical resistance and magnetoresistance over the time plays an important role in the development of these devices. However, it was observed that the structurally imperfect manganite films, such as polycrystalline [8] or very thin epitaxial [9], may undergo dramatic changes of their resistance with time which could limit their technological applicability. Moreover, for the application of the CMR-B-scalar sensors for measurements of smaller magnetic fields (b 0.5 T), the role of magnetoresistance anisotropy (MRA) significantly increases [2].…”

“…This phenomenon increases inaccuracy of measurement of magnetic field magnitude at low fields. In thin polycrystalline films the demagnetization effect depends not only on the aspect ratio of the film, but also on the magnetic interaction between grains in film plane [8,10]. Magnetic decoupling is thought to be the result of interfacial effects of grains and depends on grain boundary (GB) material which might be assumed as ferromagnetic regions with suppressed magnetic order [11] due to a high number of various defects, created during film deposition process.…”