Imaging of spin waves in atomically designed nanomagnets

Abstract

The spin dynamics of all ferromagnetic materials are governed by two types of collective phenomenon: spin waves and domain walls. The fundamental processes underlying these collective modes, such as exchange interactions and magnetic anisotropy, all originate at the atomic scale. However, conventional probing techniques based on neutron and photon scattering provide high resolution in reciprocal space, and thereby poor spatial resolution. Here we present direct imaging of standing spin waves in individual chains of ferromagnetically coupled S = 2 Fe atoms, assembled one by one on a Cu(2)N surface using a scanning tunnelling microscope. We are able to map the spin dynamics of these designer nanomagnets with atomic resolution in two complementary ways. First, atom-to-atom variations of the amplitude of the quantized spin-wave excitations are probed using inelastic electron tunnelling spectroscopy. Second, we observe slow stochastic switching between two opposite magnetization states, whose rate varies strongly depending on the location of the tip along the chain. Our observations, combined with model calculations, reveal that switches of the chain are initiated by a spin-wave excited state that has its antinodes at the edges of the chain, followed by a domain wall shifting through the chain from one end to the other. This approach opens the way towards atomic-scale imaging of other types of spin excitation, such as spinon pairs and fractional end-states, in engineered spin chains.

Quantum fluctuations stabilize skyrmion textures

“…6 we can see that both the Casimir torque as E ZP depends significantly on the uniaxial anisotropy constant K. This dependence comes from the misalignment between local spins and anisotropy easy axis. The ZP energy, and thereby the ZP Casimir spin torques, depend on the energy of the spin-wave excitations, which are interesting on their own right and could be observed by means of inelastic electron tunneling spectroscopy, as recently demonstrated for spin waves in short ferromagnetic chains [34]. …”

Nonperturbative effects and indirect exchange interaction between quantum impurities on metallic (111) surfaces

“…[1][2][3] This technique can, for example, uncover spatial profiles of magnetic excitations in artificial one-dimensional spin chains [4][5][6][7] . The surface not only supports the spin centres, but also plays a crucial role in stabilizing magnetic order [8][9][10][11] .…”

Extremely long-lived magnetic excitations in supported Fe chains

“…Indeed, atomic-scale logical devices have been assembled using atom manipulation techniques. A variety of magnetic nanostructures, and in particular of chains of magnetic atoms, have been built and analysed in STM experiments 8,9,10,11,12,13,14 that has triggered a series of associated or parallel theoretical studies 15,16,17,18,19,20,21 .…”