Influence of chromium doping on the magnetoimpedance of electrodeposited NiFeCr/Cu thin films for sensor applications

Magnetoimpedance (MI) effect in electrodeposited NiFeCr thin films on the Cu wire is studied for various doping concentrations of chromium (Cr) ion in the NiFe plating bath. The incorporation of Cr ion results in continuous reduction of crystallite size and surface roughness of the film deposited. The rms surface roughness and crystallite size of the film reduce from 33nm to 25nm and 9.1nm to 6.1nm respectively when the Cr ion concentration in plating bath is increased from zero to an optimal value of 0.06 mM. As a result, the coercivity of the film is reduced from 0.11 kA/m to 0.02 kA/m, resulting in increased magnetic softness as explained by random anisotropy model. The enhanced soft magnetic property reflects in MI ratio improved up to 313% with field sensitivity of 232%/ (kA/m) as compared to MI ratio 168% and sensitivity 104%/ (kA/m) when no Cr ion is introduced. Furthermore, an analytical model of circumferential permeability is used which considers distribution of relaxation time corresponding to domain wall motion and dispersion in circumferential magnetic anisotropy in spin rotation. Fit of the experimental data of impedance with theoretical equation of impedance in conjunction with this analytical model of circumferential permeability yields the material parameters related to circumferential permeability of NiFeCr films. These fitting parameters reveals that inclusion of Cr in permalloy film enhances its maximum value of circumferential permeability about 54% by increasing the contribution of domain wall motion and reducing the dispersion of circumferential anisotropy field.