The development of alkoxy-based sol-gel processing for magnetoresistive manganite thin films

Clothier, Brent A.

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https://hdl.handle.net/2142/17359 Copy

Description

Title

The development of alkoxy-based sol-gel processing for magnetoresistive manganite thin films

Author(s)

Clothier, Brent A.

Issue Date

2005

Doctoral Committee Chair(s)

Payne, David A.

Committee Member(s)

• Lewis, Jennifer A.
• Eckstein, James N.
• Waltraud, M. Kriven

Department of Study

Materials Science and Engineering

Discipline

Materials Science and Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Alkoxy-based
• Sol-gel
• Magnetoresistive
• Manganite
• Thin films

Language

en

Abstract

This dissertation presents, for the first time, the successful development of an all-alkoxy based, sol-gel process for integrating thin films of magnetoresistive doped-lanthanide manganites onto silicon-based substrates. Crystallization of the requisite perovskite phase at temperatures below 650°C resulted from the incorporation of all-alkoxide precursors, and in particular, Mn[OC(CH 3 ) 3 )] 2 . This latter precursor, when combined with the polyfunctional solvent, 2-methoxyethanol, exhibited high solubility and hydrolytic reactivity. This accomplishment represents a significant new contribution because low carbon-content manganese(II) alkoxides are stable, insoluble coordinate polymers. Orange and pinkish-orange solutions, also synthesized for the first time, were free from products of aerobic oxidation, and hence, contained no brown discoloration. A partial hydrolysis of h = 0.25 produced a polymeric sol system, conferring both spinnable viscosities and excellent sol longevity. Post-coating hydrolysis via humidified air proved essential to yield transparent, dense, and defect-free amorphous coatings. Conversion into a fine-grain, polycrystalline microstructure occurred above 600°C on platinized-Si(100) and above 650°C on Si(100). The cubic lattice parameters of the films (i.e., a = ∼ 3.90 Å) were in excellent agreement with values published in the literature for bulk, polycrystalline powders. Typical grain sizes started at 10-15 nm, increasing to 20-25 nm by 750°C. For films deposited on Si(100), magnetoresistance was observed in specimens heat treated at 700°C and 750°C, and for platinized-Si(100), 650°C, 700°C, and 750°C. Magnetoresistive response improved with heat-treatment temperature for the more refractory La0.67Ba 0.33 MnO 3 composition. The lead-doped counterpart offered the best property evolution, with T C = 320 K and T IM = 254 K by 750°C on platinized-Si(100). All corresponding transport curves were symmetric, demonstrating clear metal-insulator transitions (i.e., T IM ). High resistivities (i.e., ∼ 10 6 Ω-cm) were attributed to the fine-grain microstructure. Weak-field cycling between ±500 Oe yielded symmetrical loops with appreciable linear regions, a highly-desirable characteristic for magnetic sensing applications.

Type of Resource

text

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http://hdl.handle.net/2142/17359

Copyright and License Information

Copyright 2005 Brent A. Clothier

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