Microstructure, magnetoresistance, and magnetic properties of pulsed-laser-deposited external, internal, and mixed-doped lanthanum manganite films

Journal Article · Wed Sep 01 00:00:00 EDT 1999 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.371208· OSTI ID:6194705

Pietambaram, S V; Kumar, D; Singh, R K ^[1]; Lee, C B ^[2]; Kaushik, V S ^[3]

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1. Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611-6400 (United States)
2. Department of Electrical Engineering, North Carolina AT State University, Greensboro, North Carolina 27411 (United States)
3. MRST Device Engineering Division, Motorola Inc., Austin, Texas (United States)

In this article we report our studies on the microstructure, magnetoresistance (MR) behavior, and magnetic properties of the La[sub 1[minus]x[minus]y]Ca[sub x]MnO[sub 3] system in thin-film form. By varying the values of [ital x] and [ital y] in La[sub 1[minus]x[minus]y]Ca[sub x]MnO[sub 3], we have synthesized an external- (x=0.3, y=0), an internal- (x=0, y=0.3), and a mixed-doped (x=0.2, y=0.1) system with the same Mn[sup 3+]/Mn[sup 4+] ratio. Thin films of these materials have been grown [ital in situ] on (100) LaAlO[sub 3] substrates using a pulsed-laser-deposition technique. Atomic force microscopy, x-ray diffraction and high-resolution transmission electron microscopy measurements carried out on these films have shown that the films are smooth, highly crystalline, and epitaxial on the (100) LaAlO[sub 3] substrates. Electrical resistance and magnetoresistance have been measured in the 10[endash]300 K range in magnetic fields up to 5 T using a superconducting quantum interference device magnetometer. The MR ratios (calculated using the expression, [R[sub 0][minus]R[sub H]]/R[sub H], where R[sub 0] and R[sub H] are resistances in zero and applied fields) of the La[sub 0.7]Ca[sub 0.3]MnO[sub 3] (x=0.3, y=0), La[sub 0.7]MnO[sub 3] (x=0, y=0.3), and La[sub 0.7]Ca[sub 0.2]MnO[sub 3] (x=0.2, y=0.1) films are found to be 825[percent], 700[percent], and 750[percent] at 200, 240, and 220 K, respectively. The MR ratios of these films, calculated using the expression, [R[sub 0][minus]R[sub H]]/R[sub H], are 91[percent], 87[percent], and 88[percent], respectively, at the same temperatures. The variation in the insulator-to-metal transition and the MR ratio is attributed to internal chemical pressure and vacancy localization effects. Below T[sub c]/2 (T[sub c] is paramagnetic-to-ferromagnetic transition temperature), resistance increases as T[sup 2] for La[sub 0.7]Ca[sub 0.3]MnO[sub 3] and La[sub 0.7]Ca[sub 0.2]MnO[sub 3] while it increases as T[sup 5/2] for La[sub 0.7]MnO[sub 3]. The T[sup 2] and T[sup 5/2] dependence of resistance suggests that the transport is predominantly governed by an electron[endash]electron scattering and a combination of electron[endash]electron, electron[endash]phonon, and electron[endash]magnon scattering, respectively. High-temperature resistance has been observed to be consistent with small polaron hopping conductivity for all three systems. Magnetization measurements carried out on the films show that the films have reasonably square hysteresis loops with sharp T[sub c][close quote]s. Below T[sub c]/2, the magnetization decreases as T[sup 2] for La[sub 0.7]Ca[sub 0.2]MnO[sub 3] and La[sub 0.7]MnO[sub 3], suggesting single-particle excitations in them, while it decreases as T[sup 3/2] for La[sub 0.7]Ca[sub 0.3]MnO[sub 3], representing collective oscillations in this system. [copyright] [ital 1999 American Institute of Physics.]

• OSTI ID: 6194705
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Vol. 86:6; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
ALKALINE EARTH METAL COMPOUNDS
ATOMIC FORCE MICROSCOPY
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
COHERENT SCATTERING
DIFFRACTION
DOPED MATERIALS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTRON MICROSCOPY
ELECTRON-ELECTRON INTERACTIONS
FILMS
INTERACTIONS
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
LEPTON-LEPTON INTERACTIONS
MAGNETIZATION
MAGNETORESISTANCE
MAGNONS
MANGANESE COMPOUNDS
MANGANESE OXIDES
MATERIALS
MICROSCOPY
MICROSTRUCTURE
OXIDES
OXYGEN COMPOUNDS
PARTICLE INTERACTIONS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
QUASI PARTICLES
RARE EARTH COMPOUNDS
SCATTERING
THIN FILMS
TRANSITION ELEMENT COMPOUNDS
TRANSMISSION ELECTRON MICROSCOPY
X-RAY DIFFRACTION