Multilayer lanthanide-cyclooctatetraene organometallic clusters, Ln(n)(C8H8) (Ln = Eu, Tb, Ho, Tm; n = 1-7; m = n - 1, n, n + 1) were produced by a laser vaporization synthesis method. The magnetic deflections of these organometallic sandwich clusters were measured by a molecular beam magnetic deflection technique. Most of the sandwich species displayed one-sided deflection, while some of smaller Ln-C8H8 clusters showed symmetric broadening without or with only very small (or absent) net high-field deflection. In general, the total magnetic moments, calculated from. the magnitude of the beams deflections, increase with the number of lanthanide atoms (i.e., with increasing sandwich layers); however for Tb-, Ho-, and Tm-C8H8 clusters with n > 3, the suppression of the magnetic moments was observed, possibly through antiferromagnetic interactions. For Eu-C8H8 clusters, we observe a linear increase of the magnetic moments with the number of Eu atoms up to n = 7, with average magnetic moment per Eu atom around 7 mu(B)-similar to that displayed by conventionally synthesized mononuclear (EuC8H8)-C-II complexes, indicating that Eu atoms exist as Eu2+ ions in the full sandwich Eu-n(C8H8)(n+1) clusters. These results suggest that Eu-n(C8H8)(n+1) is a promising candidate for a high-spin, one-dimensional building block in organometallic magnetic materials.