Magnetic head with a spin torque oscillator, magnetic sensor, and magnetic recording/reproducing apparatus

A magnetic head, comprising:

• a spin-torque oscillator,
• the spin-torque oscillator comprising a first ferromagnetic layer, a second ferromagnetic layer, a third ferromagnetic layer provided on the opposite side of the second ferromagnetic layer from the first ferromagnetic layer, a first nonmagnetic layer provided between the first ferromagnetic layer and the second ferromagnetic layer, a second nonmagnetic layer provided between the second ferromagnetic layer and the third ferromagnetic layer, a first electrode provided on a surface on the opposite side of the first ferromagnetic layer from the first nonmagnetic layer, and a second electrode provided on a surface on the opposite side of the third ferromagnetic layer from the second nonmagnetic layer,
• wherein the second ferromagnetic layer and the third ferromagnetic layer are antiferromagnetically coupled to each other via the second nonmagnetic layer, magnetization directions of the first ferromagnetic layer and the second ferromagnetic layer are antiparallel to each other when current is not applied between the first and second electrodes, and magnetization precession is induced in each of the first through third ferromagnetic layers when current is applied between the first and second electrodes, and
• wherein a magnetic moment of the third ferromagnetic layer is larger than a magnetic moment of the second ferromagnetic layer.