A molecular beam of multilayer metal-benzene organometallic clusters M-n(C6H6)(m) (M = Al, Sc, Ti, and V) was produced by a laser vaporization synthesis method, and their magnetic deflections were measured. Multidecker sandwich clusters of transition-metal atoms and benzene Sc-n(C6H6)(n+1) (n = 1, 2) and V-n(C6H6)(n+1) (n = 1-4) possess magnetic moments that increase monotonously with n. The magnetic moments of Al(C6H6), Sc-n(C6H6)(n+1), and V-n(C6H6)(n+1) are smaller than that of their spin-only values as a result of intracluster spin relaxation, an effect that depends on the orbital angular momenta and bonding characters of the orbitals containing electron spin. While Ti(C6H6)(2) was found to be nonmagnetic, Ti-n(C6H6)(n+1) (n = 2, 3) possess nonzero magnetic moments. The mechanism of ferromagnetic spin ordering in M-2(C6H6)(3) (M = Sc, Ti, V) is discussed qualitatively in terms of molecular orbital analysis. These sandwich species represent a new class of one-dimensional molecular magnets in which the transition-metal atoms are formally zerovalent.