Gao, A.Arrington, J.Beise, E.J.Bray, B.Carr, R.W.Filippone, B.W.Lung, A.McKeown, R.D.Mueller, B.Pitt, M.L.Jones, C.E.DeSchepper, D.Dodson, G.Dow, K.Ent, R.Farkhondeh, M.Hansen, J.-O.Korsch, W.Kramer, L.H.Lee, K.Makins, N.Milner, R.G.Teiger, D.R.Welch, T.P.Candell, E.Napolitano, J.Wojtsekhowski, B.B.Tripp, C.Lorenzon, W.We report a measurement of the asymmetry in spin-dependent quasielastic scattering of longitudinally polarized electrons from a polarized 3He target. The neutron magnetic form factor GMn has been extracted from the measured asymmetry based on recent PWIA calculations using spin-dependent spectral functions. Our determination of GMn at Q2=0.19 (GeV/c)2 agrees with the dipole parametrization. This experiment represents the first measurement of the neutron magnetic form factor using spin-dependent electron scattering.PhysicsElectronsNeutronsArticle