Systems, devices and methods for determining a parameter of interest of a well fluid relating to a well intersecting a subterranean formation using resonant vibration. The apparatus may include a resonator assembly. The resonator assembly may comprise a plurality of resonant tines structurally coupled to behave as a single resonator. At least one resonant tine of the plurality of resonant tines may include a soft magnetic tine head comprising soft magnetic material uncontained by a supporting surface. Each corresponding tine of the plurality of resonant tines may be formed by at least the resonant tine head and a tine shaft. Each corresponding tine may have a cross section perpendicular to a longitudinal axis of the corresponding tine, the cross section including a tine head, where the cross section has a substantially continuous material composition. Each tine shaft may terminate at the tine head.