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The M{\o}ller polarimeter in Hall A at Jefferson Lab in Newport News, VA, hasprovided reliable measurements of electron beam polarization for the past twodecades reaching the typically required $\pm$1\% level of absolute uncertainty.However, the upcoming proposed experimental program including MOLLER and SoLIDhave stringent requirements on beam polarimetry precision at the level of 0.4\%\cite{MOLLER2014, SoLID2019}, requiring a systematic re-examination of all thecontributing uncertainties.  M{\o}ller polarimetry uses the double polarized scattering asymmetry of apolarized electron beam on a target with polarized atomic electrons. The targetis a ferromagnetic material magnetized to align the spins in a given direction.In Hall A, the target is a pure iron foil aligned perpendicular to the beam andmagnetized out of plane parallel or antiparallel to the beam direction. Theacceptance of the detector is engineered to collect scattered electrons closeto 90$^{\circ}$ in the center of mass frame where the analyzing power is amaximum (-7/9).  One of the leading systematic errors comes from determination of the targetfoil polarization. Polarization of a magnetically saturated target foilrequires knowledge of both the saturation magnetization and $g^\prime$, theelectron $g$-factor which includes components from both spin and orbitalangular momentum from which the spin fraction of magnetization is determined.This paper utilizes the existing world data to provide a best estimate fortarget polarization for both nickel and iron foils including uncertainties inmagnetization, high-field and temperature dependence, and fractionalcontribution to magnetization from orbital effects. We determine the foilelectron spin polarization at 294~K to be 0.08020$\pm$0.00018 (@4~T appliedfield) for iron and 0.018845$\pm0.000053$ (@2~T applied field) for nickel.

Accurate Determination of the Electron Spin Polarization In Magnetized Iron and Nickel Foils for M{\o}ller Polarimetry