Magnetic damping is of critical importance for devices that seek to exploit the electronic spin degree of freedom, as damping strongly a ects the energy required and speed at which a device can operate. However, theory has struggled to quantitatively predict the damping, even in common ferromagnetic materials 1-3 . This presents a challenge for a broad range of applications in spintronics 4 and spin-orbitronics that depend on materials and structures with ultra-low damping 5,6 . It is believed that achieving ultra-low damping in metallic ferromagnets is limited by the scattering of magnons by the conduction electrons. However, we report on a binary alloy of cobalt and iron that overcomes this obstacle and exhibits a damping parameter approaching 10 −4 , which is comparable to values reported only for ferrimagnetic insulators 7,8 . We explain this phenomenon by a unique feature of the band structure in this system: the density of states exhibits a sharp minimum at the Fermi level at the same alloy concentration at which the minimum in the magnetic damping is found. This discovery provides both a significant fundamental understanding of damping mechanisms and a test of the theoretical predictions proposed by Mankovsky and colleagues 3 .In recent decades, several theoretical approaches have attempted to quantitatively predict magnetic damping in metallic systems. One of the early promising theories was that of Kambersky, who introduced the so-called breathing Fermi-surface model 9-11 . More recently, Gilmore and Stiles 2 as well as Thonig et al. 12 demonstrated a generalized torque correlation model that includes both intraband (conductivity-like) and interband (resistivity-like) transitions. The use of scattering theory to describe damping was later applied by Brataas et al. 13 and Liu et al. 14 to describe damping in transition metals. A numerical realization of a linear response damping model was implemented by Mankovsky 3 for Ni-Co, Ni-Fe, Fe-V and Co-Fe alloys. For the Co-Fe alloy, these calculations predict a minimum intrinsic damping of α int ≈ 0.0005 at a Co-concentration of 10% to 20%, but was not experimentally observed 15 .Underlying this theoretical work is the goal of achieving new systems with ultra-low damping that are required in many magnonic and spin-orbitronics applications 7,8 . Ferrimagnetic insulators such as yttrium-iron-garnet (YIG) have long been the workhorse for these investigations, because YIG films as thin as 25 nm have experimental damping parameters as low as 0.9 × 10 −4 (ref. 16). Such ultra-low damping can be achieved in insulating ferrimagnets in part due to the absence of conduction electrons-and, therefore, the suppression of magnon-electron scattering. However, insulators cannot be used in most spintronic and spin-orbitronic applications, where a charge current through the magnetic material is required, nor is the requirement of growth on gadolinium gallium garnet templates compatible with spintronics and complementary metal-oxide semiconductor (CMOS) fabrication processes. One...

Using a first-principles Green's function approach we study magnetic properties of the magnetic binary tetradymite chalcogenides Bi 2 Se 3 , Bi 2 Te 3 , and Sb 2 Te 3 . The magnetic coupling between transition-metal impurities is long range, extends beyond a quintuple layer, and decreases with increasing number of d electrons per 3d atom. We find two main mechanisms for the magnetic interaction in these materials: the indirect exchange interaction mediated by free carriers and the indirect interaction between magnetic moments via chalcogen atoms. The calculated Curie temperatures of these systems are in good agreement with available experimental data. Our results provide deep insight into exchange interactions in magnetic binary tetradymite chalcogenides and open a way to design new materials for promising applications.

Heusler compounds are exciting materials for future spintronics applications because they display a wide range of tunable electronic and magnetic interactions. Here, we use a femtosecond laser to directly transfer spin polarization from one element to another in a half-metallic Heusler material, Co2MnGe. This spin transfer initiates as soon as light is incident on the material, demonstrating spatial transfer of angular momentum between neighboring atomic sites on time scales < 10 fs. Using ultrafast high harmonic pulses to simultaneously and independently probe the magnetic state of two elements during laser excitation, we find that the magnetization of Co is enhanced, while that of Mn rapidly quenches. Density functional theory calculations show that the optical excitation directly transfers spin from one magnetic sublattice to another through preferred spin-polarized excitation pathways. This direct manipulation of spins via light provides a path toward spintronic devices that can operate on few-femtosecond or faster time scales.

We present a computationally efficient general first-principles based method for spin-lattice simulations for solids and clusters. The method is based on a coupling of atomistic spin dynamics and molecular dynamics simulations, expressed through a spin-lattice Hamiltonian, where the bilinear magnetic term is expanded up to second order in displacement. The effect of first order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and we observe good agreement with previous simulations. In addition, we also illustrate the coupled spin-lattice dynamics method on a more conceptual level, by exploring dissipation-free spin and lattice motion of small magnetic clusters (a dimer, trimer and quadmer). The here discussed method opens the door for a quantitative description and understanding of the microscopic origin of many fundamental phenomena of contemporary interest, such as ultrafast demagnetization, magnetocalorics, and spincaloritronics. arXiv:1804.03119v2 [cond-mat.mtrl-sci] 9 Jul 2018