A magnetoresistance effect element includes a first ferromagnetic layer, a second ferromagnetic layer, and a tunnel barrier layer that is interposed between the first ferromagnetic layer and the second ferromagnetic layer. The tunnel barrier layer is a stacked body including one or more first oxide layers having a spinel structure and one or more second oxide layers having a spinel structure with a composition which is different from a composition of the first oxide layer.

An acoustic antenna is actuated by causing magnetization oscillations in magnetostrictive nanomagnets with alternating spin-orbit torque from a heavy metal nano strip supplied with an alternating current. Periodic expansion and contraction of the nanomagnets caused by the magnetization oscillation launches an acoustic wave in a piezoelectric substrate placed underneath the nanomagnets. This novel actuation mechanism allows for an extreme subwavelength acoustic antenna with a radiation efficiency over 50 times larger than the limit for an acoustic antenna actuated by an acoustic wave and operated at acoustic resonance. Antennas such as these have applications in many areas such as miniaturized speakers, micro electromechanical (MEMS) devices, acoustic mapping and analysis of biological specimens in a biochip or biosensor, etc.