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\subsection{Varying the Current}   The relationship described in Eq. \ref{eq:growthrate} can not be applied to the degree of polarization or magnetization. In order to determine whether the degree of polarization depends on the strength of magnetic field, we have to vary the current. saturation magnetization values $M_{\infty}$ as a function of polarizing field.  When varying the current, for electronic systems, the fractional populations are affected by the g-factor or the spectroscopic splitting factor. The fractional populations can be described by the lower and upper states-- $N_1$ represents the lower state and $N_2$ represents the upper state. The difference between these two states multiplied by the magnetic moment describes the magnetization of the field. The following relationship can be expressed in the equation below \cite{Kittel_1953}, \begin{equation}   \label{eq:tanh}  M=(N_1-N_2)\mu= N\mu\cdot\frac{e^x-e^{-x}}{e^x+e^{-x}}=N\mu \tanh{x}