The question of how, and how fast, magnetization can be reversed is a topic of great practical interest for the manipulation and storage of magnetic information. It is generally accepted that magnetization reversal should be driven by a stimulus represented by time-non-invariant vectors such as a magnetic field, spin-polarized electric current, or cross-product of two oscillating electric fields. However, until now it has been generally assumed that heating alone, not represented as a vector at all, cannot result in a deterministic reversal of magnetization, although it may assist this process. Here we show numerically and demonstrate experimentally a novel mechanism of deterministic magnetization reversal in a ferrimagnet driven by an ultrafast heating of the medium resulting from the absorption of a sub-picosecond laser pulse without the presence of a magnetic field.

Spin-based electronics has evolved into a major field of research that broadly encompasses different classes of materials, magnetic systems, and devices. This review describes recent advances in spintronics that have the potential to impact key areas of information technology and microelectronics. We identify four main axes of research: nonvolatile memories, magnetic sensors, microwave devices, and beyond-CMOS logic. We discuss state-of-the-art developments in these areas as well as opportunities and challenges that will have to be met, both at the device and system level, in order to integrate novel spintronic functionalities and materials in mainstream microelectronic platforms.Conventional information processing and communication devices work by controlling the flow of electric charges in integrated circuits. Such circuits are based on nonmagnetic semiconductors, in Technologies based on GMR and MTJ devices are now firmly established and compatible with CMOS fab processes. Yet, in order to meet the increasing demand for high-speed, high-density, and low power electronic components, the design of materials, processes, and spintronic circuits needs to be continuously innovated. Further, recent breakthroughs in basic research brought forward novel phenomena that allow for the generation and interconversion of charge, spin, heat, and optical signals.Many of these phenomena are based on non-equilibrium spin-orbit interaction effects, such as the spin Hall and Rashba-Edelstein effects 6,8,23 or their thermal 24 and optical 25,26 analogues. Spin-orbit torques (SOT), for example, can excite any type of magnetic materials, ranging from metals to semiconductors and insulators, in both ferromagnetic and antiferromagnetic configurations 6 . This versatility allows for the switching of single layer ferromagnets, ferrimagnets, and antiferromagnets, as well as for the excitation of spin waves and auto-oscillations in both planar and vertical device geometries 10,11 . Charge-spin conversion effects open novel pathways for information processing using Boolean logic, as well as promising avenues for implementing unconventional neuromorphic 27,28,29 and probabilistic 30 computing schemes. Finally, spintronic devices cover a broad bandwidth ranging from DC to THz 31,32 , leading to exciting opportunities for the on-chip generation and detection of high frequency signals.

The oriented attachment of magnetic nanoparticles is recognized as an important pathway in the magnetic-hyperthermia cancer treatment roadmap, thus, understanding the physical origin of their enhanced heating properties is a crucial task for the development of optimized application schemes. Here, we present a detailed theoretical analysis of the hysteresis losses in dipolar-coupled magnetic nanoparticle assemblies as a function of both the geometry and length of the array, and of the orientation of the particles' magnetic anisotropy. Our results suggest that the chain-like arrangement biomimicking magnetotactic bacteria has the superior heating performance, increasing more than 5 times in comparison with the randomly distributed system when aligned with the magnetic field. The size of the chains and the anisotropy of the particles can be correlated with the applied magnetic field in order to have optimum conditions for heat dissipation. Our experimental calorimetrical measurements performed in aqueous and agar gel suspensions of 44 nm magnetite nanoparticles at different densities, and oriented in a magnetic field, unambiguously demonstrate the important role of chain alignment on the heating efficiency. In low agar viscosity, similar to those of common biological media, the initial orientation of the chains plays a minor role in the enhanced heating capacity while at high agar viscosity, chains aligned along the applied magnetic field show the maximum heating. This knowledge opens new perspectives for improved handling of magnetic hyperthermia agents, an alternative to conventional cancer therapies.

The established methods for the numerical evaluation of magnetic material properties exist only in certain limits, including first-principles methods, spin models, and micromagnetics. In the present paper, we introduce a multiscale modeling approach, bridging the gaps between the three approaches above. The goal is to describe thermodynamic equilibrium and nonequilibrium properties of magnetic materials on length scales up to micrometers, starting from first principles. In the first step, we model, as an example, bulk FePt in the ordered Llo phase by using an effective, classical spin Hamiltonian that was constructed earlier on the basis of firstprinciples methods. The next step is to simulate this spin model by using the stochastic Landau-LifshitzGilbert equation. The temperature dependent micromagnetic parameters, which are evaluated with these atomistic simulations, are consequently used to develop a many macrospin micromagnetic approach, based on the Landau-Lifshitz-Bloch equation. As an example, we calculate the magnetization dynamics following a picosecond heat pulse resembling pump-probe experiments.

We compare femtosecond pump-probe experiments in Ni and micromagnetic modelling based on the Landau-Lifshitz-Bloch equation coupled to a two-temperature model, revealing a predominant thermal ultrafast demagnetization mechanism. We show that both spin (femtosecond demagnetization) and electron-phonon (magnetization recovery) rates in Ni increase as a function of the laser pump fluence. The slowing down for high fluences arises from the increased longitudinal relaxation time. PACS numbers: 75.40Gb,78.47.+p, The implementation of novel magnetic recording and spintronic devices requires well-funded knowledge of the limits of spin manipulation. Pump-probe experiments with powerful femtosecond lasers [1,2,3,4,5,6,7,8] have pushed these limits down to the femtosecond timescale in the past decade. These experiments have attracted many researchers with the aim to understand both fundamental mechanisms of the magnetization dynamics in a strongly out-of-equilibrium regime and to control the magnetic properties of materials on the femtosecond timescale. Very recently the involvement of the spin in thermoelectric processes, spin Peltier or Seebeck effects, has become of strong interest [9]. Therefore a vital understanding of energy transport between the spin, electron and phonon system in ferromagnets is needed. Even for the most simple itinerant ferromagnets, such as Ni, the processes connecting the elementary spin scattering process and the terahertz (THz) spin-wave generation have not been identified yet. However, they are the key to understand the macroscopic demagnetization on the femtosecond time scale.Different non-thermal mechanisms of how light could couple to the spin system have been put forward: the excitation of non-magnetic states mediated by the enhanced spin-orbit interaction (SOC) [10], the inverse Faraday [4] or the Barnet effect [11]. At the moment, no clear proof of these effects has been presented for the ultrafast magnetization dynamics in Ni: (i) The change of the light polarization has no influence on the femtosecond demagnetization and estimations suggest that the amount of direct angular momentum transfer from photons to spins is negligible [5], (ii) the time-dependent density functional theory based on the SOC mechanism at its present state of the art srongly underestimates the experimentally observed timescales in itinerant ferromagnets [10].Differenty from the latter, it has been shown that more applicable is a "thermal" ansatz for the description of the femtosecond magnetization dynamics in the itinerant ferromagnets [1,3,12,13,14]. Within this description, it is assumed that the excited state is a statistical ensemble of many electronic excitations, based on the undisputed fact that the photons of a femtosecond laser, focused on a metal, pass the energy to the subsystems of electrons, phonons and spins. Photons are absorbed by electrons close to the Fermi level leading to a non-equilibrium distribution that thermalizes within several femtoseconds. In the so-called two-temperature (2T ) model [1...