Magnetoresistance in granular films formed by CoFe and phase change material

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2013-10, Vol.113 (1), p.221-229
• Main Authors: Huang, J. C., Song, W. D., Bain, J. A., Yang, Y., Shi, L. P., Schlesinger, T. E., Chong, T. C., Hui, H. K.
• Format: Article
• Language: English
• Subjects: Annealing; Characterization and Evaluation of Materials; Cold working, work hardening; annealing, quenching, tempering, recovery, and recrystallization; textures; Columns (structural); Condensed Matter Physics; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Deposition; Diamagnetism, paramagnetism and superparamagnetism; Exact sciences and technology; Giant magnetoresistance; Granular materials; Iron; Machines; Magnetic properties and materials; Magnetoresistance; Magnetoresistivity; Magnetotransport phenomena, materials for magnetotransport; Manufacturing; Materials science; Nanotechnology; Optical and Electronic Materials; Physics; Physics and Astronomy; Processes; Surfaces and Interfaces; Thin Films; Treatment of materials and its effects on microstructure and properties
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-012-7522-1

Magnetoresistance having a field and current dependence like that of GMR (but a rather small magnitude) has been observed in Co 70 Fe 30 /GeTe and Co 70 Fe 30 /Ge 2 Sb 2 Te 5 granular films. Film stacks were fabricated using tandem (multilayer) deposition and annealing was required for the films to develop the GMR-type response. This GMR-type behavior is distinct from AMR, which is observed before annealing. With films having the structure [CoFe 4 nm/GeTe 6 nm] 10 , a magnetoresistance (MR) of 0.19 %, which has the GMR-type character can be observed after an optimal annealing temperature of 450 °C. TEM and X-ray reflectometry suggest that columnar granules with layered Fe form during deposition and with annealing. Magnetoresistive transport is believed to be between the discontinuous layers in each columnar grain. These discontinuous layers are observed to be superparamagnetic in SQUID ZFC-FC measurements measured from 5–300 K. Magnetoresistance can be fitted by the quadratic relation appropriate for GMR in granular films, especially at higher GeTe compositions. When Ge 2 Sb 2 Te 5 is used instead of GeTe, higher anneal temperatures are required before the MR with GMR character appears. This GMR type response does not appear when pure Fe is used instead of the CoFe alloy, with the samples showing only AMR in this case. This is due to the absence of Co which seems to cause a more granular growth.