Organizing nanometer-scale magnets with bacterial threads

• Published in: IEEE transactions on magnetics 1998-07, Vol.34 (4), p.988-990
• Main Authors: Smith, C.J., Field, M., Coakley, C.J., Awschalom, D.D., Mendelson, N.H., Mayes, E.L., Davis, S.A., Mann, S.
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Interfacial magnetic properties (multilayers, magnetic quantum wells, superlattices, magnetic heterostructures); Iron; Magnetic anisotropy; Magnetic field induced strain; Magnetic particles; Magnetic properties and materials; Magnetic properties of surface, thin films and multilayers; Magnets; Microorganisms; Organizing; Perpendicular magnetic anisotropy; Physics; Temperature
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/20.706333

Macroscopic magnetic bacterial threads are formed in which 10 nm Fe/sub 3/O/sub 4/ particles are intercalated between cell walls. A mutant strain of bacteria is used which forms long filaments of joined cells. Using a drawing technique these strands can be bound together to form a solid thread which can be used as superstructure to template magnetic particles. Dipping a thread into a ferrofluid solution allows the thread to rehydrate and draw the magnetite particles between the filaments. Cross-sectional images of the redrawn threads show the strands of cells form an ordered structure along the length of the fiber and reveal the magnetic particles embedded between the cell walls. The composite bacterial thread is superparamagnetic with a blocking temperature T/sub B//spl sim/175 K. Below this temperature the magnetization displays a field-dependent hysteresis indicating anisotropic behavior.