We demonstrate using inelastic scanning tunneling spectroscopy and simulations based on density functional theory that the amplitude and sign of the magnetic anisotropy energy for a single Fe atom adsorbed onto the Pt(111) surface can be manipulated by modifying the adatom binding site. Since the magnitude of the measured anisotropy is remarkably small, up to an order of magnitude smaller than previously reported, electron-hole excitations are weak and thus the spin excitation exhibits long lived precessional lifetimes compared to the values found for the same adatom on noble metal surfaces.

Chiral magnets are a promising route towards dense magnetic storage technology due to their inherent nano-scale dimensions and energy efficient properties. Engineering chiral magnets requires atomic-level control of the magnetic exchange interactions, including the Dzyaloshinskii–Moriya interaction, which defines a rotational sense for the magnetization of two coupled magnetic moments. Here we show that the indirect conduction electron-mediated Dzyaloshinskii–Moriya interaction between two individual magnetic atoms on a metallic surface can be manipulated by changing the interatomic distance with the tip of a scanning tunnelling microscope. We quantify this interaction by comparing our measurements to a quantum magnetic model and ab-initio calculations yielding a map of the chiral ground states of pairs of atoms depending on the interatomic separation. The map enables tailoring the chirality of the magnetization in dilute atomic-scale magnets.

The recently proposed theoretical concept of a Hund's metal is regarded as a key to explain the exotic magnetic and electronic behavior occuring in the strongly correlated electron systems of multiorbital metallic materials. However, a tuning of the abundance of parameters, that determine these systems, is experimentally challenging. Here, we investigate the smallest possible realization of a Hund's metal, a Hund's impurity, realized by a single magnetic impurity strongly hybridized to a metallic substrate. We experimentally control all relevant parameters including magnetic anisotropy and hybridization by hydrogenation with the tip of a scanning tunneling microscope and thereby tune it through a regime from emergent magnetic moments into a multi-orbital Kondo state. Our comparison of the measured temperature and magnetic field dependent spectral functions to advanced many-body theories will give relevant input for their application to non-Fermi liquid transport, complex magnetic order, or unconventional superconductivity.1 arXiv:1604.03854v1 [cond-mat.str-el] Apr 2016Recent examples of exotic phases of matter, including unconventional superconductivity in iron pnictides and chalcogenides [1][2][3] as well as non-Fermi liquid behavior in ruthenates [4][5][6], depend subtly on the complex interplay of magnetic moments and delocalized electron states taking place in transition metal d-shells. All these materials combine sizable Coulomb interactions and hybridization, which are comparable in their strength. In such cases, it is generally unclear, to which extent local magnetic moments exist, how they can be described using quantum impurity models [7], and how far electronic correlation effects such as Kondo screening [8,9] modify material properties, particularly magnetism, as a function of temperature and magnetic field. The recent concept of a Hund's metal [2,10,11] has been introduced in order to describe exactly this regime, where charge fluctuations in the orbitals are not negligible due to the presence of strong hybridization, but where local magnetic moments can still survive.The fundamental constituent of such a Hund's metal is a magnetic impurity strongly coupled to the electron states of a metallic host, which we coin Hund's impurity. This concept is described in the following for the particular case of a 3d transition metal atom that gets adsorbed (adatom) onto a metallic substrate (Fig. 1). If the atom is still in the gas phase an integer number of electrons is filled into the five 3d orbitals according to Hund's first rule: [12,13] The orbitals are first filled up by electrons having the same spin, before being filled with the remaining electrons of opposite spin. This is driven by the intraatomic exchange energy, or so-called Hund's rule exchange J Hund , which has to be paid if one of the electron spins is flipped. If the 3d transition metal atom is adsorbed onto the metallic substrate, electrons can hop on or off of these orbitals into the bath of substrate conduction electrons, which has ...

Non-collinear spin states with unique rotational sense, such as chiral spin-spirals, are recently heavily investigated because of advantages for future applications in spintronics and information technology and as potential hosts for Majorana Fermions when coupled to a superconductor. Tuning the properties of such spin states, e.g., the rotational period and sense, is a highly desirable yet difficult task. Here, we experimentally demonstrate the bottom-up assembly of a spin-spiral derived from a chain of iron atoms on a platinum substrate using the magnetic tip of a scanning tunneling microscope as a tool. We show that the spin-spiral is induced by the interplay of the Heisenberg and Dzyaloshinskii-Moriya components of the Ruderman-Kittel-Kasuya-Yosida interaction between the iron atoms. The relative strengths and signs of these two components can be adjusted by the interatomic iron distance, which enables tailoring of the rotational period and sense of the spin-spiral.

A cluster of a few magnetic atoms on the surface of a nonmagnetic substrate is one suitable realization of a bit for spin-based information technology. The prevalent approach to achieve magnetic stability is decoupling the cluster spin from substrate conduction electrons in order to suppress destabilizing spin-flips. However, this route entails less flexibility in tailoring the coupling between the bits needed for spin-processing. Here, we use a spin-resolved scanning tunneling microscope to write, read, and store spin information for hours in clusters of three atoms strongly coupled to a substrate featuring a cloud of non-collinearly polarized host atoms, a so-called non-collinear giant moment cluster. The giant moment cluster can be driven into a Kondo screened state by simply moving one of its atoms to a different site. Using the exceptional atomic tunability of the non-collinear substrate mediated Dzyaloshinskii–Moriya interaction, we propose a logical scheme for a four-state memory.