This radio-frequency oscillator includes a magnetoresistive device in which an electric current is able to flow. The magnetoresistive device includes a first magnetic layer, known as a “trapped layer”, whereof the magnetization is of fixed direction. The magnetoresistive device further includes a second magnetic layer known as a “free layer” and a non-magnetic layer, known as an “intermediate layer”, interposed between the first and second layer, known as the intermediate layer. The oscillator further includes means capable of causing an electron current to flow in said layers constituting the aforementioned stack and in a direction perpendicular to the plane which contains said layers. One of the three layers constituting the magnetoresistive device includes at least one constriction zone of the electric current passing through it.