A magnetic head assembly includes: a magnetic recording head, a head slider, a suspension and an actuator arm. The magnetic recording head includes a spin torque oscillator and a main magnetic pole. The spin torque oscillator includes, a first magnetic layer including at least one selected from the group consisting of a Fe—Co—Al alloy, a Fe—Co—Si alloy, a Fe—Co—Ge alloy, a Fe—Co—Mn alloy a Fe—Co—Cr alloy and a Fe—Co—B alloy, a second magnetic layer, and an intermediate layer provided between the first magnetic layer and the second magnetic layer. The main magnetic pole is placed together with the spin torque oscillator. The magnetic recording head is mounted on the head slider. The head slider is mounted on one end of the suspension. The actuator arm is connected to other end of the suspension.