Exchange bias magnetism in films of NiFe/(Ni,Fe)O nanocrystallite dispersions

Journal Article · Wed May 07 00:00:00 EDT 2014 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4868184· OSTI ID:22275587

Hsiao, C. -H.; Chi, C. -C.; Wang, S.; Desautels, R. D.; Lierop, J. van ^[1]; Lin, K. -W. ^[2]; Lin, T. -L. ^[3]

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1. Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2 (Canada)
2. Department of Materials Science and Engineering, National Chung Hsing University, Taichung 402, Taiwan (China)
3. Department of Engineering and System Science, National Tsing Hua University, Hsinchu 300, Taiwan (China)

Ni{sub 3}Fe/(Ni,Fe)O thin films having a nanocrystallite dispersion morphology were prepared by a reactive ion beam-assisted deposition technique. The crystallite sizes of these dispersion-based films were observed to decrease from 8.4 ± 0.3 nm to 3.4 ± 0.3 nm as the deposition flow-rate increased from 2.78% to 7.89% O{sub 2}/Ar. Thin film composition was determined using selective area electron diffraction images and Multislice simulations. Through a detailed analysis of high resolution transmission electron microscopy images, the nanocrystallites were determined to be Ni{sub 3}Fe (a ferromagnet), NiO, and FeO (both antiferromagnets). It was determined that the interfacial molar Ni{sub 3}Fe ratio in the nanocrystallite dispersions increased slightly at first, then decreased as the oxygen content was increased; at 7.89% O{sub 2}/Ar, the interfacial molar ratio was essentially zero (only NiO and FeO remained). For nanocrystallite dispersion films grown with O{sub 2}/Ar flow-rate greater than 7.89%, no interfacial (intermixed) Ni{sub 3}Fe phase was detected, which resulted in no measurable exchange bias. Comparing the exchange bias field between the nanocrystallite dispersion films at 5 K, we observed a decrease in the magnitude of the exchange bias field as the nanocrystallite size decreased. The exchange bias coupling for all samples measured set in at essentially the same temperature (i.e., the exchange bias blocking temperature). Since the ferromagnetic/anti-ferromagnetic (FM/AFM) contact area in the nanocrystallite dispersion films increased as the nanocrystallite size decreased, the increase in the magnitude of the exchange bias could be attributed to larger regions of defects (vacancies and bond distortions) which occupied a significant portion of the FM/AFM interfaces in the nanocrystallite dispersion films.

• OSTI ID: 22275587
• Journal Information: Journal of Applied Physics, Vol. 115, Issue 17; Conference: 55. annual conference on magnetism and magnetic materials, Atlanta, GA (United States), 14-18 Nov 2010; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
77 NANOSCIENCE AND NANOTECHNOLOGY
ANTIFERROMAGNETIC MATERIALS
ATOMIC FORCE MICROSCOPY
COMPARATIVE EVALUATIONS
ELECTRON DIFFRACTION
FERROMAGNETIC MATERIALS
INTERFACES
INTERMETALLIC COMPOUNDS
ION BEAMS
IRON
IRON OXIDES
MAGNETISM
NANOSTRUCTURES
NICKEL
NICKEL OXIDES
OXYGEN
THIN FILMS
TRANSMISSION ELECTRON MICROSCOPY
VACANCIES