Radiofrequency oscillator incorporating: - a magnetoresistive device through which a spin-polarized electric current flows in order to generate an oscillating signal at a frequency of oscillation on an output terminal, this device comprising a stack of at least: • a first magnetic layer, referred to as the "reference layer", capable of spin-polarizing the electric current and the magnetization of which is of fixed direction; • a second magnetic layer, referred to as the "free layer", the magnetization of which may oscillate when the spin-polarized current flows therethrough; and • a non-magnetic layer, referred to as the "spacer", interposed between the two preceding layers in order to form a tunnel junction or spin valve; - a current source (4; 104) for causing a current of electrons to flow through said layers perpendicularly to the latter; - a terminal (18; 102) for controlling the frequency or the amplitude of the oscillating signal, said control terminal acting on the intensity of the current source or on a characteristic of a magnetic field specifically for modifying the frequency of oscillation or the amplitude of the oscillating signal, this magnetic field being generated by a generator that is arranged with respect to the device so that the field lines of the magnetic field generated thereby pass through the free layer of the device; - a control loop connected between the output terminal and the control terminal in order to apply, to the control terminal, a control signal so as to slave a characteristic of the oscillating signal to a reference value, characterized in that the control loop includes: - a sensor for detecting the amplitude of the oscillations of the oscillating signal; and - a comparator capable of generating the control signal according to the measured amplitude and the reference value: - by directly comparing the measured amplitude with a reference value of the amplitude so as to control the oscillating signal in terms of amplitude; or - by comparing a measured frequency N(Aosc) with a reference frequency, where the measured frequency N(Aosc) is the result of a conversion of the measured amplitude to a measured frequency using a predetermined relationship N. - a magnetoresistive device through which a spin-polarized electric current flows in order to generate an oscillating signal at a frequency of oscillation on an output terminal, this device comprising a stack of at least: • a first magnetic layer, referred to as the "reference layer", capable of spin-polarizing the electric current and the magnetization of which is of fixed direction; • a second magnetic layer, referred to as the "free layer", the magnetization of which may oscillate when the spin-polarized current flows therethrough; and • a non-magnetic layer, referred to as the "spacer", interposed between the two preceding layers in order to form a tunnel junction or spin valve; • a first magnetic layer, referred to as the "reference layer", capable of spin-polarizing the electric current and the magnetization of which is of fixed direction; • a second magnetic layer, referred to as the "free layer", the magnetization of which may oscillate when the spin-polarized current flows therethrough; and • a non-magnetic layer, referred to as the "spacer", interposed between the two preceding layers in order to form a tunnel junction or spin valve; - a current source (4; 104) for causing a current of electrons to flow through said layers perpendicularly to the latter; - a terminal (18; 102) for controlling the frequency or the amplitude of the oscillating signal, said control terminal acting on the intensity of the current source or on a characteristic of a magnetic field specifically for modifying the frequency of oscillation or the amplitude of the oscillating signal, this magnetic field being generated by a generator that is arranged with respect to the device so that the field lines of the magnetic field generated thereby pass through the free layer of the device; - a control loop connected between the output terminal and the control terminal in order to apply, to the control terminal, a control signal so as to slave a characteristic of the oscillating signal to a reference value, - a sensor for detecting the amplitude of the oscillations of the oscillating signal; and - a comparator capable of generating the control signal according to the measured amplitude and the reference value: - by directly comparing the measured amplitude with a reference value of the amplitude so as to control the oscillating signal in terms of amplitude; or - by comparing a measured frequency N(Aosc) with a reference frequency, where the measured frequency N(Aosc) is the result of a conversion of the measured amplitude to a measured frequency using a predetermined relationship N.