The practical difficulty in distinguishing the impact of magnetic circular dichroism and the inverse Faraday effect fuels intense debates over which mechanism predominantly drives the process of helicity dependent all-optical switching of magnetization in ferromagnets. Here, we quantitatively measure the efficiency of the switching process in a Pt/Co/Pt multilayered stack using visible- to near-infrared optical pulses. We find that the switching efficiency increases by a factor of 8.6 upon increasing the pumping wavelength from 0.5 $ \mu $m to 1.1 $ \mu $m, becoming 100 % efficient at even longer wavelengths up to 2.0 $ \mu $m. Our experimental results can be successfully explained by the phenomenon of magnetic circular dichroism, making a significant step towards resolving the long-standing controversy over the origin of the all-optical process of magnetization reversal in ferromagnets.

The A-site organic components of organic-inorganic hybrid metal halides (OIHMHs) significantly impact their crystal structure and optoelectronic properties. However, chemical modification of A-site cations has been mostly limited to commercial organic precursors, which restricts the structural variability of OIHMHs for optimal functionalities. Herein we have proposed an extendable synthesis approach to the direct procurability of various organic cations with desireable structures for the in situ construction of a library of OIHMH materials. The template condensation reaction between dimethyl sulfoxide and acetone derivatives yields A-site organic cations with exquisite control of modularization and regioselectivity within the OIHMH crystallization system. The as-fabricated OIHMHs demonstrated highly efficient linear optical photoluminescence or nonlinear optical second harmonic generation, promising potential applications in photonic devices. This in situ synthetic strategy offers a structural extension of OIHMHs and establishes a fundamental methodological platform for screening functional OIHMH materials.

Finding methods for the most efficient and fastest detection and control of magnetic domains in antiferromagnets is presently among the main challenges of magnetic research at large. We analyse the problem of optical read-out and control of the antiferromagnetic Néel vector using symmetry analysis and the principles of equilibrium thermodynamics. Following the pioneering approach of Dzyaloshinksii, we divide all antiferromagnets in three classes. It is shown that, using the magneto-optical Faraday effect or other effects which scale linearly with the antiferromagnetic Néel vector, it is possible to distinguish antiferromagnetic domains with mutually opposite Néel vectors in two of the three classes. Symmetry properties of one of these two classes are similar to those of altermagnets. The analysis also reveals multiple mechanisms to directly excite spins with light for practically every type of antiferromagnet.

The drastic shape deformation that accompanies the structural phase transition in thermosalient materials offers great potential for their applications as actuators and sensors. The microscopic origin of this fascinating effect has so far remained obscure, while for technological applications, it is important to learn how to drive transitions from one phase to another. Here, we present a combined computational and experimental study, in which we have successfully identified the order parameter for the thermosalient phase transition in the molecular crystal 2,7-di([1,1'-biphenyl]-4-yl)fluorenone. Molecular dynamics simulations reveal that the transition barrier vanishes at the transition temperature. The simulations further show that two low-frequency vibrational-librational modes are directly related to the order parameter that describes this phase transition, which is supported by experimental Raman spectroscopy studies. By applying a computational THz pulse with the proper frequency and amplitude we predict that we can photoinduce this phase transition on a picosecond timescale. Significance 2,7-di([1,1'-biphenyl]-4-yl)fluorenone (4DBpFO) crystals exhibit a remarkably rapid solid-state phase transition resulting in a crystal jump. So far the underlying atomistic mechanism is poorly understood, making it an intriguing subject for study. Computationally, we have successfully identified the molecular motions driving the phase transition in 4DBpFO. The transition barrier vanishes at the transition temperature. The simulations predict that the transition can be induced by applying a pulse at the resonant frequency of the relevant motions far below the transition temperature. This brings a high level of control over the phase transition and our computational approach should be transferable to other systems to predict how to selectively trigger changes in these materials.

Controlling magnetic textures at ever smaller length and time scales is of key fundamental and technological interest. Achieving nanoscale control often relies on finding an external stimulus that is able to act on that small length scales, which is highly challenging. A promising alternative is to achieve nanoscale control using the inhomogeneity of the magnetic texture itself. Using a multilayered ferromagnetic Pt/Co/Pt thin-film structure as a model system, we employ a magnetic force microscope to investigate the change in magnetic nanotextures induced by circularly polarized picosecond laser pulses. Starting from a saturated magnetic state, we find stochastic nucleation of complex nanotextured domain networks. In particular, the growth of these domains depends not only on their macroscopic magnetization but also on the complexity of the domain texture. This helicity and texture-dependent effect contrasts with the typical homogeneous growth of magnetic domains initiated by an effective magnetic field of a circularly polarized laser pulse. We corroborate our findings with a stochastic model for the nucleation of magnetic domains, in which the nucleation and annihilation probability not only depends on the helicity of light but also on the relative magnetization orientation of neighboring domains. Our results establish a new approach to investigate ultrafast nanoscale magnetism and photo-excitation across first-order phase transitions.

Exploiting the ability of optical second harmonic generation (SHG) to visualize antiferromagnetic domains in Cr2O3, here we explore the potential of SHG to probe the THz-induced ultrafast spin dynamics in this antiferromagnet. Our experiments clearly show that the observed THz-induced SHG transients do not reflect the dynamics of the antiferromagnetic N & eacute;el vector. Moreover, depending on the helicity of light at the fundamental frequency, the transients may have different form, corresponding either to linear or quadratic dependence of the SHG intensity on the THz electric field.

The effect of optical rectification (OR) in the terahertz range (THz rectification, TR) is experimentally demonstrated. The effect consists of generating a DC voltage on the faces of a ferroelectric triglycine sulfate (TGS) single crystal under the action of pulsed radiation with a frequency of 1.57 and 1.96 THz and an electric field strength per pulse of 1.3 and 1.5 MV/m, respectively. The FLARE FELIX free-electron laser system (Radboud University, The Netherlands) was used as a THz radiation source. The TR effect makes it possible to directly determine the nonlinear susceptibilities of media (including those under conditions of strong absorption) without any reference or optical channel calibration and also without the need of Fourier transform.

Both temperature (T ) increase and/or application of an external magnetic field (H) are able to induce ferromagnetism in otherwise antiferromagnetic FeRh. We present a theory that allows us to predict H -T phase diagrams for FeRh, with a special emphasis on the canted antiferromagnetic phase. Both cases of in-plane and out-of-plane magnetic anisotropy in FeRh films are studied numerically, and the results of the simulations are compared with the results obtained via magneto-transport studies done in magnetic fields up to 34 T and x-ray magnetic circular dichroism measured at the Rh L2,3 and Fe K absorption edges in magnetic fields up to 17 T. The comparisons suggest examples of the simulated H -T phase diagrams that are most suitable to fit the case of FeRh.

Magnetic skyrmions are particle‐like topological magnetic textures that are potential information carriers in future spintronics. An enormous body of research confirms their existence in a broad range of magnetic materials since their first discovery in 2009. To date, magnetic skyrmions can not only be found in asymmetric systems but also in centrosymmetric ones. Notably, engineered magnetic multilayers are promising structures for skyrmion‐based spintronics because they can stabilize small‐sized skyrmions at room temperature and facilitate their electric manipulation. In this overview, we introduce the topological nature, their special properties, and nucleation methods of skyrmions, and show their potential for applications. Perspectives on skyrmionic devices and developments toward other, more three‐dimensional particle‐like magnetic nanostructures, are discussed at the end.

Ever since the first observation of all-optical switching of magnetization in the ferrimagnetic alloy GdFeCo using femtosecond laser pulses, there has been significant interest in exploiting this process for data-recording applications. In particular, the ultrafast speed of the magnetic reversal can enable the writing speeds associated with magnetic memory devices to be potentially pushed towards THz frequencies. This work reports the development of perpendicular magnetic tunnel junctions incorporating a stack of Tb/Co nanolayers whose magnetization can be all-optically controlled via helicity-independent single-shot switching. Toggling of the magnetization of the Tb/Co electrode was achieved using either 60 femtosecond-long or 5 picosecond-long laser pulses, with incident fluences down to 3.5 mJ/cm2, for Co-rich compositions of the stack either in isolation or coupled to a CoFeB-electrode/MgO-barrier tunnel-junction stack. Successful switching of the CoFeB-[Tb/Co] electrodes was obtained even after annealing at 250 °C. After integration of the [Tb/Co]-based electrodes within perpendicular magnetic tunnel junctions yielded a maximum tunneling magnetoresistance signal of 41% and RxA value of 150 Ωμm2 with current-in-plane measurements and ratios between 28% and 38% in nanopatterned pillars. These results represent a breakthrough for the development of perpendicular magnetic tunnel junctions controllable using single laser pulses, and offer a technologically-viable path towards the realization of hybrid spintronic-photonic systems featuring THz switching speeds.

It is shown using the technique of double high-speed photography that an external magnetic field triggers the motion of a GdFeCo domain wall with a velocity up to 1.2 km/s. The domain wall velocity increases and levels off with an increase in the amplitude of the driving magnetic-field pulse. In contrast to the earlier experiments on iron ferrites, no influence of femtosecond laser pulses on the domain wall dynamics has been observed, even when the pump pulse energy is sufficient for magnetization reversal.

Recent works have shown that the magnetization of Tb/Co multilayers can be switched all-optically by a single ultrashort laser pulse. Surprisingly, the same process cannot be achieved in TbCo alloys. Here, we present a plausible explanation for this difference in behavior based on the known treatment of angular momenta and the associated gyromagnetic ratio of rare-earth-based ferrimagnets. We then study in detail the composition-dependent dynamic behavior of the switching process in Tb/Co multilayers using single-shot time-resolved pump-probe experiments. We show that the observed dynamics is strongly dependent on the excitation fluence and multilayer composition and does not fit into the accepted framework describing the single-shot switching process found in Gd-based systems and Mn-containing Heusler alloys.

[This corrects the article DOI: 10.1021/acsphotonics.7b01402.].

Using the technique of double high-speed photography method, we show that an external magnetic field triggers in GdFeCo domain wall motion with velocities up to 1.2 km / s. The domain wall velocity saturates with an increase of the driving magnetic field. Contrary to earlier experiments on iron garnets, we did not succeed to detect any effect of femtosecond laser pulses on the domain wall velocity, even if the pulses were strong enough to reverse magnetization.

CoPS3 stands out in the family of the van der Waals antiferromagnets XPS3 (X=Mn, Ni, Fe, Co) due to the unquenched orbital momentum of the magnetic Co2+ ions which is known to facilitate the coupling of spins to both electromagnetic waves and lattice vibrations. Here, using a time-resolved magneto-optical pump-probe technique we experimentally study the ultrafast laser-induced dynamics of mutually correlated spins and lattice. It is shown that a femtosecond laser pulse acts as an ultrafast heater and thus results in the melting of the antiferromagnetic order. At the same time, the resonant pumping of the 4T1g - 4T2g electronic transition in Co2+ ions effectively changes their orbital momentum, giving rise to a mechanical force that moves the ions in the direction parallel to the orientation of their spins, thus generating a coherent Bg phonon mode at the frequency of about 4.7 THz.

Using diffraction of femtosecond laser pulses of visible light by a magnetic domain pattern in an iron garnet, we demonstrate a proof of concept of time-resolved measurements of domain pattern movements with nanometer spatial and femtosecond temporal resolution. In this method, a femtosecond laser (pump) pulse initiates magnetization dynamics in a sample that is initially in a labyrinth domain state, while an equally short linearly polarized laser pulse (probe) is diffracted by the domain pattern. The components of the diffracted light that are polarized orthogonally to the incident light generate several concentric diffraction rings. Nanometer small changes in the relative sizes of domains with opposite magnetization result in observable changes in the intensities of the rings. We demonstrate that the signal-to-noise ratio is high enough to detect a 6 nm domain wall displacement with 100 fs temporal resolution using visible light. We also discuss possible artifacts, such as pump-induced changes of optical properties, that can affect the measurements.

The massive use of artificial neural networks (ANNs), increasingly popular in many areas of scientific computing, rapidly increases the energy consumption of modern high-performance computing systems. An appealing and possibly more sustainable alternative is provided by novel neuromorphic paradigms, which directly implement ANNs in hardware. However, little is known about the actual benefits of running ANNs on neuromorphic hardware for use cases in scientific computing. Here we present a methodology for measuring the energy cost and compute time for inference tasks with ANNs on conventional hardware. In addition, we have designed an architecture for these tasks and estimate the same metrics based on a state-of-the-art analog in-memory computing (AIMC) platform, one of the key paradigms in neuromorphic computing. Both methodologies are compared for a use case in quantum many-body physics in two dimensional condensed matter systems and for anomaly detection at 40 MHz rates at the Large Hadron Collider in particle physics. We find that AIMC can achieve up to one order of magnitude shorter computation times than conventional hardware, at an energy cost that is up to three orders of magnitude smaller. This suggests great potential for faster and more sustainable scientific computing with neuromorphic hardware.