Zero-point magnetic exchange interactions

Quantum fluctuations are ubiquitous in physics. Ranging from conventional examples like the harmonic oscillator to intricate theories on the origin of the universe, they alter virtually all aspects of matter, including superconductivity, phase transitions, and nanoscale processes. As a rule of thumb, the smaller the object, the larger its impact. This poses a serious challenge to modern nanotechnology, which aims at total control via atom-by-atom engineered devices. In magnetic nanostructures, high stability of the magnetic signal is crucial when targeting realistic applications in information technology, e.g., miniaturized bits. Here we show that zeropoint spin fluctuations play an important role in determining the fundamental magnetic exchange interactions that dictate the nature and stability of the magnetic state. Based on the fluctuation-dissipation theorem, we show that quantum fluctuations correctly account for the large overestimation of the interactions as obtained from conventional static first-principles frameworks, filling in an important gap between theory and experiment Zhou et al., Nat. Phys. 6, 187 (2010); Khajetoorians et al., ibid. 8, 497 (2012). Our analysis further reveals that zero-point spin fluctuations tend to promote the noncollinearity and stability of chiral magnetic textures such as skyrmions, a counterintuitive quantum effect that inspires practical guidelines for designing disruptive nanodevices.