Magnetostatically Induced Easy-Cone Magnetic State Tuning by Perpendicular Magnetic Anisotropy in an Unbiased Spin-Torque Diode

We report the magnetostatically induced formation of an easy-cone magnetic state in free layers of magnetic tunneling junction (MTJ) with only first-order perpendicular magnetic anisotropy. By means of micromagnetic modeling, we study easy-cone angle dependence on the first-order anisotropy and its impact on the microwave sensitivity of the unbiased spin-torque diode. Considered magnetization tilt can be effectively engineered by choosing the ratio of the shape and first-order surface anisotropy, defined by the free layer's thickness, in-plane MTJ shape, and interlayer magnetostatic interactions. Through micromagnetic modeling over a broad range of input powers and free-layer thicknesses, we demonstrate a significant role of nonlinearity and inhomogeneous magnetization dynamics in achieving high sensitivity levels. Our modeling for typical state-of-the-art parameters of MTJ shows a possibility to reach a record-breaking unbiased sensitivity of 1100 mV/mW and 4650 mV/mW after impedance matching, which is far beyond the parameters of commercial Schottky diodes. These results will be very helpful for the development of efficient spintronic ambient energy harvesters.