Abstract
Interfacial perpendicular magnetic anisotropy, which is characterized by first-order (K1) and second-order (K2) anisotropy, is the core phenomenon for nonvolatile magnetic devices. A sizable K2 satisfying a specific condition stabilizes the easy-cone state, where equilibrium magnetization forms at an angle from the film normal. The easy-cone state offers intriguing possibilities for advanced spintronic devices and unique spin textures, such as spin superfluids and easy-cone domain walls. Experimental realization of the easy-cone state requires understanding the origin of K2, thereby enhancing K2. However, the previously proposed origins of K2 cannot fully account for the experimental results. Here, we experimentally show that K2 scales almost linearly with the work function difference between the Co and X layers in Pt/Co/X heterostructures (X = Pd, Cu, Pt, Mo, Ru, W, and Ta), suggesting the central role of the inversion asymmetry in K2. Our result provides a guideline for enhancing K2 and realizing magnetic applications based on the easy-cone state.
Highlights
Magnetic anisotropy describes a magnetization-angledependent change in magnetic energy and stabilizes the magnetization in specific directions
In thin-film heterostructures such as ferromagnet/normal metal bilayers where the structural inversion symmetry is broken at the interface, the magnetic anisotropy is dominated by interfacial contributions, as follows: EðθÞ 1⁄4 K1eff sin2θ þ K2sin4θ ð1Þ
The out-of-plane state originating from perpendicular magnetic anisotropy (PMA) has been a main focus of spintronics research[2] because it offers scalable magnetic random-access memories (MRAMs)[3]
Summary
Magnetic anisotropy describes a magnetization-angledependent change in magnetic energy and stabilizes the magnetization in specific directions. The out-of-plane state originating from perpendicular magnetic anisotropy (PMA) has been a main focus of spintronics research[2] because it offers scalable magnetic random-access memories (MRAMs)[3]. Interest in another state—the easy-cone state, where the equilibrium magnetization direction is tilted from the film normal and forms a cone—has increased for the following reasons. It provides improved functionalities of various spintronics devices, such as low-power operation of spin-transfer torque (STT) MRAMs4–6 and zerofield precession of STT oscillators[7]. The existence of the easycone state was experimentally verified in various layered
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