Giant Magnetoimpedance (GMI)

 
When a static magnetic field Hdc is applied to a magnetic conductor, a change in the total impedance of the material is observed. This leads to Magnetoimpedance (MI) phenomena. If an a.c. current flows through the conductor, a transverse magnetic field (Hac) is generated by Ampere’s law. This Hac will in turn induce some magnetization. The MI can be written as

V = RI + VL

where VL is the inductive voltage generated due to transverse magnetization. The field dependence of MI can be explained in terms of the skin depth

where c is the velocity of light, is the angular frequency of the a.c. current, the conductivity and the permeability. The MI effect wasn’t of much interested since early 90’s when Panina et.al. reported a huge MI effect in amorphous ferromagnetic wires at low frequencies for small applied magnetic field.

where Hmaxis usually the external magnetic field sufficient to saturate the impedance. In practice, the value of is available for given experimental equipment.


Fig. 1. (a) The impedance (Z) and (b) GMI ratio [ΔZ/Z(%)] change as a function of external magnetic field (H) for a Fe71Al2Si14B8.5Cu1Nb3.5 nanocrystalline ribbon.


Fig. 2. The definition of impedance
Relevant Papers

• Panina LV, Mohri K. Magneto-impedance effect in amorphous wires. Appl Phys Lett 1994;65:1189–91

• Phan MH, Peng HX, Wisnom MR, Yu SC, Chau N. Enhanced GMI effect in a Co70Fe5Si15B10 ribbon due to Cu and Nb substitution for B. Phys Stat Sol A 2004;201:1558–62.

• Phan M-H, Peng H-X, Giant magnetoimpedance materials: Fundamentals and application Prog Mater Sci (2007), doi:10.1016/j.pmatsci.2007.05.003
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