Experiments show that the natural frequency of a beam-plate in a transverse static magnetic field decreases to near zero as the field attains a critical value which causes the same plate to buckle statically. Under an oscillating magnetic field the beam-plate is observed to become unstable and perform parametrically excited oscillations. A mathematical model based on a quasistatic solution for the magnetization in the deformed plate is proposed. The theoretical results agree very well with the experimental data. It is shown that the phenomena are analogous to those for a beam-column under static and dynamic axial forces.