A perpendicular magnetic recording hard disk drive includes a write head with a write pole and an electrically conductive coil coupled to the write pole, a write driver for supplying electrical write current to the coil to generate magnetic flux in the write pole, a spin torque oscillator (STO) that injects auxiliary magnetic flux to the write pole to facilitate magnetization switching of the write pole, and STO control circuitry. Direct electrical current to the STO induces rotation of the magnetization of a free ferromagnetic layer in the STO, which generates the auxiliary magnetic flux. The STO control circuitry may be coupled to the STO via the electrical lines that connect the write driver to the write head, the lines that connect the read amplifier to the read head, or, if the disk drive is one with thermal fly-height control (TFC), the lines that connect the TFC circuitry with the heater.