Abstract: Resonators magnetically tunable over a broad rf frequency range capable of operation at relatively low rf frequencies (VHF band) are disclosed as well as tunable devices based on them. The resonators comprise a resonator body made of a ferrimagnetic single-crystal material which is generally flat, and is generally rotationally symmetrical with respect to an axis of rotation, for example disk-like or oblate spheroidal-like. The axis of rotation of the resonator body is oriented with respect to the crystalline lattice in a particular way depending on the anisotropy. The same orientation is required for the dc field whose magnitude determines the resonance frequency. The resonators are particularly useful in broadband tunable rf and microwave filters and oscillators, and can be tuned by means of the dc field to resonate from about 50 MHz to several GHz.