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Magnetic materials play a vital role in energy-efficient data storage technologies, combining very fast switching with long-term retention of information. However, it has been shown that, at very short time scales, magnetisation dynamics become chaotic due to internal instabilities, resulting in incoherent spin-wave excitations that ultimately destroy magnetic ordering. Here, contrary to expectations, we show that such chaos gives rise to a periodic pattern of reversed magnetic domains, with a feature size far smaller than the spatial extent of the excitation. We explain this pattern as a result of phase-synchronisation of magnon-polaron quasiparticles, driven by strong coupling of magnetic and elastic modes. Our results reveal not only the peculiar formation and evolution of magnon-polarons at short time-scales, but also present an alternative mechanism of magnetisation reversal driven by coherent packets of short-wavelength magnetoelastic waves. Increasing the speed of magnetization switching is an obvious pathway to improve spintronic device performance. However, very fast magnetization switching is accompanied by instabilities. Here, Gidding et al study these instabilities using optical pumping, and show that instability generated spin-waves can achieve a high enough amplitude to drive switching of the magnetization, with a distinctive coherent pattern.

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/cm 2 , 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 Ω μ m 2 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.

All-optical magnetization reversal with femtosecond laser pulses facilitates the fastest and least dissipative magnetic recording, but writing magnetic bits with spatial resolution better than the wavelength of light has so far been seen as a major challenge. Here, we demonstrate that a single femtosecond laser pulse of wavelength 800 nm can be used to toggle the magnetization exclusively within one of two 10-nm thick magnetic nanolayers, separated by just 80 nm, without affecting the other one. The choice of the addressed layer is enabled by the excitation of a plasmon-polariton at a targeted interface of the nanostructure, and realized merely by rotating the polarization-axis of the linearly-polarized ultrashort optical pulse by 90°. Our results unveil a robust tool that can be deployed to reliably switch magnetization in targeted nanolayers of heterostructures, and paves the way to increasing the storage density of opto-magnetic recording by a factor of at least 2. The density of magnetic storage media is limited by the superparamagnetic limit when scaling down magnetic bits. Here, the authors open the way for stacked magnetic storage by using all-optical switching and addressing different magnetic layers by polarization-dependent excitation of plasmon-polaritons.

Over the last two decades, breakthrough works in the field of non-linear phononics have revealed that high-frequency lattice vibrations, when driven to high amplitude by mid- to far-infrared optical pulses, can bolster the light-matter interaction and thereby lend control over a variety of spontaneous orderings. This approach fundamentally relies on the resonant excitation of infrared-active transverse optical phonon modes, which are characterized by a maximum in the imaginary part of the medium’s permittivity. Here, in this Perspective article, we discuss an alternative strategy where the light pulses are instead tailored to match the frequency at which the real part of the medium’s permittivity goes to zero. This so-called epsilon-near-zero regime, popularly studied in the context of metamaterials, naturally emerges to some extent in all dielectric crystals in the infrared spectral range. We find that the light-matter interaction in the phononic epsilon-near-zero regime becomes strongly enhanced, yielding even the possibility of permanently switching both spin and polarization order parameters. We provide our perspective on how this hitherto-neglected yet fertile research area can be explored in future, with the aim to outline and highlight the exciting challenges and opportunities ahead.

The historic Barnett effect describes how an inertial body with otherwise zero net magnetic moment acquires spontaneous magnetization when mechanically spinning 1 , 2 . Breakthrough experiments have recently shown that an ultrashort laser pulse destroys the magnetization of an ordered ferromagnet within hundreds of femtoseconds 3 , with the spins losing angular momentum to circularly polarized optical phonons as part of the ultrafast Einstein–de Haas effect 4 , 5 . However, the prospect of using such high-frequency vibrations of the lattice to reciprocally switch magnetization in a nearby magnetic medium has not yet been experimentally explored. Here we show that the spontaneous magnetization gained temporarily by means of the ultrafast Barnett effect, through the resonant excitation of circularly polarized optical phonons in a paramagnetic substrate, can be used to permanently reverse the magnetic state of a heterostructure mounted atop the said substrate. With the handedness of the phonons steering the direction of magnetic switching, the ultrafast Barnett effect offers a selective and potentially universal method for exercising ultrafast non-local control over magnetic order. Ultrafast light-induced driving of phonons at resonance in a substrate facilitates the permanent reversal of the magnetic state of a material mounted on it.

Strong light–matter interaction constitutes the bedrock of all photonic applications, empowering material elements with the ability to create and mediate interactions of light with light. Amidst the quest to identify new agents facilitating such efficient light–matter interactions, a class of promising materials has emerged, featuring highly unusual properties deriving from their dielectric constant ε being equal, or at least very close, to zero. Works so far have shown that the enhanced nonlinear optical effects displayed in this epsilon-near-zero (ENZ) regime make it possible to create ultrafast albeit transient optical switches. An outstanding question, however, relates to whether one could use the amplification of light–matter interactions at the ENZ conditions to achieve permanent switching. Here we demonstrate that an ultrafast excitation under ENZ conditions can induce permanent all-optical reversal of ferroelectric polarization between different stable states. Our reliance on ENZ conditions that naturally emerge from the solid’s ionic lattice suggests that the demonstrated mechanism of reversal is truly universal, being capable of permanently switching order parameters in a wide variety of systems. Researchers reveal that naturally emerging epsilon-near-zero conditions in BaTiO 3 can be exploited to drive permanent all-optical switching of ferroelectric polarization. The general nature of the epsilon-near-zero regime means that the approach could be used to switch spontaneous order parameters in other systems.

Identifying efficient pathways to control and modify the order parameter of a macroscopic phase in materials is an important ongoing challenge. One way to do this is via the excitation of a high-frequency mode that couples to the order, and this is the ultimate goal of the field of ultrafast phase transitions1,2. This is an especially interesting research direction in magnetism, where the coupling between spin and lattice excitations is required for magnetization reversal3,4. However, previous attempts5,6 have not demonstrated switching between magnetic states via resonant pumping of phonon modes. Here we show how an ultrafast resonant excitation of the longitudinal optical phonon modes in magnetic garnet films switches magnetization into a peculiar quadrupolar magnetic domain pattern, revealing the magneto-elastic mechanism of the switching. In contrast, the excitation of strongly absorbing transverse phonon modes results in a thermal demagnetization effect only.Resonant excitation of phonons by a laser pulse switches the magnetization of a thin yttrium iron garnet film. This particular combination of longitudinal optical phonons results in a quadrupolar pattern, but this could be tailored in the future.

Existing accounts of Rochester’s early years are thin or in error in terms of historical context. His father was a notable Royalist exile and favorite of Charles II—indeed, his companion on his flight from Worcester in 1651. His own childhood was spent under the aegis of his mother in the household of her first husband. Rochester’s enrollment at Wadham College, Oxford, was probably a precaution against the possibility that General Lambert’s radical army would return triumphant from its confrontation with Monck’s troops on the Scottish border and exact revenge on Royalist houses. He was given extraordinary prominence in the university’s collections of verses celebrating the restoration of the monarchy and again in the triumphalist degree ceremony of 1661. Indeed, Rochester’s treatment at Oxford bordered on what would have been appropriate for a royal prince. The Lee connection, and especially the background presence of his mother, also remained important, even during the years of Rochester’s “debauchery.”

Objective: To report on the effectiveness of an initiative to reduce deaths from sudden cardiac arrest occurring in busy public places. Setting: 110 such places identified from ambulance service data as high risk sites. Patients: 172 members of the public who developed cardiac arrest at these sites between April 2000 and March 2004. 20 592 defibrillator months’ use is reported, representing one automated external defibrillator (AED) use every 120 months. Intervention: 681 AEDs were installed; staff present at the sites were trained in basic life support and to use AEDs. Main outcome measures: Initial rhythm detected by AED, restoration of spontaneous circulation, survival to hospital discharge. Results: 172 cases of cardiac arrest were treated by trained lay staff working at the site before the arrival of the emergency services during the period. A shockable rhythm was detected in 135 (78%), shocks being administered in 134 an estimated 3–5 minutes after collapse; 38 (28.3%) patients subsequently survived to hospital discharge. Spontaneous circulation was restored in five additional patients who received shocks but died later in hospital. In 37 cases no shock was initially indicated; one patient survived after subsequent treatment by paramedics, cardiopulmonary resuscitation having been given soon after collapse. Overall, irrespective of the initial rhythm, 39 patients (22.7%), were discharged alive from hospital. For witnessed arrests of presumed cardiac cause in ventricular fibrillation (an international Utstein comparator) survival was 37 of 124 (29.8%). Conclusions: The use of AEDs by lay people at sites where cardiac arrest commonly occurs is an effective strategy to reduce deaths at these sites.

Generalized anxiety disorder (GAD) and panic disorder (PD) differ in their biology and co-morbidities. We hypothesized that GAD but not PD symptoms at the age of 15 years are associated with depression diagnosis at 18 years. Using longitudinal data from the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort we examined relationships of GAD and PD symptoms (measured by the Development and Well-Being Assessment) at 15 years with depression at 18 years (by the Clinical Interview Schedule - Revised) using logistic regression. We excluded adolescents already depressed at 15 years and adjusted for social class, maternal education, birth order, gender, alcohol intake and smoking. We repeated these analyses following multiple imputation for missing data. In the sample with complete data (n = 2835), high and moderate GAD symptoms in adolescents not depressed at 15 years were associated with increased risk of depression at 18 years both in unadjusted analyses and adjusting for PD symptoms at 15 years and the above potential confounders. The adjusted odds ratio (OR) for depression at 18 years in adolescents with high relative to low GAD scores was 5.2 [95% confidence interval (CI) 3.0-9.1, overall p < 0.0001]. There were no associations between PD symptoms and depression at 18 years in any model (high relative to low PD scores, adjusted OR = 1.3, 95% CI 0.3-4.8, overall p = 0.737). Missing data imputation strengthened the relationship of GAD symptoms with depression (high relative to low GAD scores, OR = 6.2, 95% CI 3.9-9.9) but those for PD became weaker. Symptoms of GAD but not PD at 15 years are associated with depression at 18 years. Clinicians should be aware that adolescents with GAD symptoms may develop depression.