Spin-Torque Oscillator Based on Magnetic Tunnel Junction with a Perpendicularly Magnetized Free Layer and In-Plane Magnetized Polarizer

Abstract

We fabricated a spin-torque oscillator (STO) having a nanopillar-shaped magnetic tunnel junction with perpendicularly magnetized FeB free and in-plane magnetized CoFeB reference layers. The perpendicular magnetization of the FeB was stabilized by strong perpendicular magnetic anisotropy induced at both the MgO tunnel barrier/FeB and FeB/MgO cap interfaces. Under a perpendicular field (3 kOe), the STO exhibited a large emission power (0.55 W), a high frequency (6.3 GHz) and a high Q factor (135) simultaneously, all of which are the largest to date among nanopillar-shaped STOs. The bias voltage dependence of the oscillation property was well explained by the macrospin model.

Linewidth of power spectrum originated from thermal noise in spin torque oscillator

“…On the other hand, the linewidth above I c monotonically decreases as the current increases, whereas that below I c depends nonmonotonically on the current. Such complex current dependence of the linewidth was found in previous experimental studies [7,26]. Above I c , the length of the precession trajectory becomes long as the current, as well as the cone angle, increases.…”

“…The Q-factor reaches 10 4 for the current I ≃ 10 mA, which is two orders of magnitude larger than the experimentally observed value (135 in Ref. [7]). This result should motivate future experimental research for practical STO applications.…”

“…2 (a) is, at maximum, about 100 MHz. On the other hand, the experimental value is, at minimum, 50 MHz, and is typically much wider than 100 MHz [7]. This fact indicates that other physical mechanisms contribute to the linewidth in the experiments.…”

“…Recently, it was found [7,8] that an STO with a perpendicularly magnetized free layer and an in-plane magnetized pinned layer [9][10][11][12][13][14] can achieve a large emission power of close to 1 µW. Therefore, this type of STO will be the model structure for practical STO applications.…”

Mutual synchronization of spin-torque oscillators consisting of perpendicularly magnetized free layers and in-plane magnetized pinned layers

“…The synchronization of spin-torque oscillators results in an enhancement of the emission power and an increase of the quality factor of the practical devices. In addition, new applications such as brain-inspired computing based on the synchronized spin-torque oscillators are proposed very recently [16][17][18][19].An attractive structure of spin-torque oscillator for practical applications is that consisting of a perpendicularly magnetized free layer and an in-plane magnetized pinned layer [20][21][22] because this type of spin-torque oscillator results in high emission power, narrow linewidth, and wide frequency tunability simultaneously. The oscillation properties of this type of spin-torque oscillator, such as the relation between the injected current and the oscillation frequency, as a single oscillator have been investigated both experimentally [22] and theoretically [23].…”