Automatic measurement of field-dependent elastic modulus and damping by laser Doppler vibrometry

A method for characterizing the magnetoelastic dependence of both Young's modulus and damping on the magnetic field is presented. It is based on laser Doppler vibrometry and free longitudinal vibration in soft ferromagnetic rods and wires, and offers a broad range of improved features including accuracy, lack of interaction with the sample, speed of measurement, full automation, high resolution and the possibility of stress-dependence studies. All these allow samples to be perfectly characterized in the full magnetic field range, estimating the behaviour of the specimen as different magnetization curves are followed and discovering critical points that had been overlooked in previous works. As an example, the magnetoelastic characterization of nickel rods is described, and excellent results are obtained which are consistent with the hysteresis loop of nickel and the theory of magnetic domains in ferromagnetic materials.