Nuclear-resonance-fluorescence spectra have been measured in the chain of {sup 148,150,152,154}Sm isotopes. Together with supplementary information from inelastic electron scattering and other reaction studies, orbital {ital M}1 transition strengths have been deduced for a number of 1{sup +} states located around an excitation energy of 3 MeV. The systematic study, carried out for the first time, for nuclei within a large range of the deformation parameter {delta} shows that the orbital {ital M}1 strength varies quadratically with {delta}. This result is interpreted in terms of models containing explicitly neutron and proton degrees of freedom.