A spin torque magnetoresistive sensor having a very small gap thickness. The sensor operates by measuring the change in frequency of a spin torque induced magnetic oscillation in magnetic layers of the sensor to detect the presence of a magnetic field. The sensor includes a pair of free magnetic layers that are antiparallel coupled by a thin non-magnetic coupling layer there-between. The sensor does not include a pinned layer structure nor an associated AFM pinning layer, which allows the sensor to be constructed much thinner than prior art sensors.