Advances in Characterization of Non-Rare-Earth Permanent Magnets: Exploring Commercial Alnico Grades 5–7 and 9


The magnetic domain structure of commercial alnico grades 5–7 and 9 was investigated using a magneto-optical Kerr effect (MOKE) to gain an understanding of their coercivity mechanisms at the micron to millimeter scale. In alnico 5–7, the magnetic domain structure exhibits stripes of alternating high and low induction. Magnetic domains easily cross grain boundaries if neighboring grains have a similar tilt and rotation of their crystallographic axes relative to the magnet body. In contrast for alnico 9, stripe-like magnetic domains are not observed regularly throughout the transverse section; rather, discrete localization of high- and low-induction stripe features are observed. In higher magnification MOKE experiments, i.e., ~100 μm, a zigzag-shaped magnetic domain structure was observed in both alnico 5–7 and 9. The zigzag features are four to five times smaller in size than an average grain of alnico 5–7, implying a pinning mechanism that is caused by structural elements within the grains. Discontinuous and reversible motion on a length scale of a few microns was observed for the zigzag-shaped domains for incremental changes in the applied field of ~10 Oe. Complimentary magnetic force microscopy measurements show that there are domain structures on an even smaller scale, i.e., 2 μm to 100 μm.

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We are greatly indebted to Fran Laabs (Ames Laboratory) for OIM data collection and assistance in data analysis. This work was supported by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy (EERE), under its Vehicle Technologies Program, through the Ames Laboratory. The Ames Laboratory is operated by Iowa State University under Contract DE-AC02-07CH11358.

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Correspondence to I. E. Anderson.

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Palasyuk, A., Blomberg, E., Prozorov, R. et al. Advances in Characterization of Non-Rare-Earth Permanent Magnets: Exploring Commercial Alnico Grades 5–7 and 9. JOM 65, 862–869 (2013).

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  • Domain Wall
  • Magnetic Domain
  • Magnetic Force Microscopy
  • Orientation Imaging Microscopy
  • Magnetic Domain Structure