Remnant Magnetisation varying with input amplitude

[Cortizza]

In a lab we had to measure the remnant magnetisation of a hysteresis loop with a permalloy core. The amplitude of the input sinusoidal wave was varied and the resulting remnant magnetisation measured. This was then plotted resulting in the remnant magnetisation varying sinusoidal with the input amplitude. When the core was changed to silver steel or mild steel the sinusoidal relationship no longer occured.
Why did the remnance vary sinusoidally with amplitude only for the permalloy sample?

 

[berkeman]

In a lab we had to measure the remnant magnetisation of a hysteresis loop with a permalloy core. The amplitude of the input sinusoidal wave was varied and the resulting remnant magnetisation measured. This was then plotted resulting in the remnant magnetisation varying sinusoidal with the input amplitude. When the core was changed to silver steel or mild steel the sinusoidal relationship no longer occured.
Why did the remnance vary sinusoidally with amplitude only for the permalloy sample?

Welcome to the PF.

Have you found datasheets or other technical information on those core materials? You should be able to find Google Images showing the hysteresis curves as you increase the amplitude of the excitation.

 

[Charles Link]

I'm not sure of your definition of "remnant magnetization", but it sounds like you were basically measuring $\chi_m(\omega)$ , where $\vec{M}(\omega)=\chi_m(\omega) \vec{H}(\omega)$. The vector $\vec{H}(\omega)$ is the applied magnetic field at frequency $\omega$ from the solenoid. And $\chi_m(\omega)$ is the magnetic susceptibility=it is in general frequency dependent. ( Presumably you measured $\chi_m(\omega)$ for only one specific frequency, which is ok).$\\$ In the first case, you must have had a material where the response was linear, so that $\chi_m(\omega)$ is a constant for a given frequency (sometimes a complex one, so that a phase delay can be included in the response). $\\$ For the other materials, it is likely they are more like a permanent magnet, where no such linear response occurs. You simply can not write a linear equation for these materials relating $\vec{M}(\omega)$ to $\vec{H}(\omega)$. $\\$ There is one additional item that may be worth including if you have any mathematical background in linear response theory: The equation $\vec{M}(t)=\int\limits_{- \infty}^{t} \chi_m(t-t') \vec{H}(t') \, dt'$ is applicable if the system responds linearly. The equation $\vec{M}(\omega)=\chi_m(\omega) \vec{H}(\omega)$ follows from the convolution theorem, where in this last equation, these are all Fourier transforms of the quantities of the integral equation.