An electromagnetic device is provided for use, for example, as a yarn brake, a rely nozzle valve, a weft yarn stretching nozzle and the like. The electromagnetic device has a pole piece associated with a winding connectable to an electric line. A spring strip is fixedly mounted at one end and projects over a curved abutment surface on the pole piece. In the absence of a magnetic field, the spring strip is disposed in spaced relation to the abutment surface. When a magnetic field builds up in the winding and the pole piece, the free end portion of the strip engages with the abutment surface of the pole piece along an increasing length, for example, to brake a yarn therebetween and, as the magnetic field intensifies, more and more zones of the spring strip engage the pole piece. Consequently, the initial speeds at which the strip moves at engagement and upon cessation of energization of the winding are relatively high.