Large magnetocrystalline anisotropy in tetragonally distorted Heuslers: a systematic study

With a view to the design of hard magnets without rare earths we explore the possibility of large magnetocrystalline anisotropy energies in Heusler compounds that are unstable with respect to a tetragonal distortion. We consider the Heusler compounds Fe$_2$YZ with Y = (Ni, Co, Pt), and Co$_2$YZ with Y = (Ni, Fe, Pt) where, in both cases, Z = (Al, Ga, Ge, In, Sn). We find that for the Co$_2$NiZ, Co$_2$PtZ, and Fe$_2$PtZ families the cubic phase is always, at $T=0$, unstable with respect to a tetragonal distortion, while, in contrast, for the Fe$_2$NiZ and Fe$_2$CoZ families this is the case for only 2 compounds -- Fe$_2$CoGe and Fe$_2$CoSn. For all compounds in which a tetragonal distortion occurs we calculate the MAE finding remarkably large values for the Pt containing Heuslers, but also large values for a number of the other compounds (e.g. Co$_2$NiGa has an MAE of -2.11~MJ/m$^3$). The tendency to a tetragonal distortion we find to be strongly correlated with a high density of states at the Fermi level in the cubic phase. As a corollary to this fact we observe that upon doping compounds for which the cubic structure is stable such that the Fermi level enters a region of high DOS, a tetragonal distortion is induced and a correspondingly large value of the MAE is then observed.Comment: 8 pages, 5 figure

Storytelling as a research tool and intervention around public health perceptions and behaviour: a protocol for a systematic narrative review

INTRODUCTION There is a growing trend to use storytelling as a research tool to extract information and/or as an intervention to effect change in the public knowledge, attitudes and behaviour (KAB) in relation to public health issues, primarily those with a strong element of disease prevention. However, evidence of its use in either or both capacities is limited. This protocol proposes a systematic narrative review of peer-reviewed, published literature on the use of storytelling as a research tool within the public health arena. METHODS AND ANALYSIS Medline, EMBASE, PsycINFO, ERIC (Educational Resources Information Center), Web of Science, Art and Humanities database (ProQuest), Scopus and Google Scholar will be searched for studies that look at the use of storytelling in the research of pressing current public health issues, for example, vaccinations, antimicrobial resistance, climate change and cancer screening. The review will synthesise evidence of how storytelling is used as a research tool to (a) gain insights into KAB and (b) to effect change in KAB when used as an intervention. Included studies will be selected according to carefully defined criteria relevant to public health issues of interest, and data from qualitative, quantitative and mixed-methods studies will be extracted with a customised data extraction form. A narrative synthesis will be performed according to Economic and Social Research Council guidance from Popay, J, 2006.The study protocol follows the recommendations by the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P). ETHICS AND DISSEMINATION Formal ethical approval is not required for this study, as no primary data will be collected. Dissemination will involve publishing results of this study in relevant peer-reviewed journal(s). Where possible, the study results will also be presented as posters or talks at relevant medical conferences and meetings. PROSPERO REGISTRATION NUMBER CRD4201912470

Electronic origin of x-ray absorption peak shifts

Encoded in the transient x-ray absorption (XAS) and magnetic circular (MCD) response functions resides a wealth of information of the microscopic processes of ultrafast demagnetization. Employing state-of-the-art first-principles dynamical simulations we show that the experimentally observed energy shift of the L3 XAS peak in Ni, and the absence of a corresponding shift in the dichroic MCD response, can be explained in terms of laser-induced changes in band occupation. Strikingly, we predict that for the same ultrashort pump pulse applied to Co the opposite effect will occur: a substantial shift upward in energy of the MCD peaks will be accompanied by very small change in the position of XAS peaks, a fact we relate to the reduced d-band filling of Co that allows a greater energetic range above the Fermi energy into which charge can be excited. We also carefully elucidate the dependence of this effect on pump pulse parameters. These findings (i) establish an electronic origin for early-time peak shifts in transient XAS and MCD spectroscopy and (ii) illustrate the rich information that may be extracted from transient response functions of the underlying dynamical system

Ab initio study of ultrafast spin dynamics in Gd_x(FeCo)_1−x alloys

Using an ultrashort laser pulse, we explore ab initio the spin dynamics of Gdx(FeCo)1-x at femtosecond time scales. Optical excitations are found to drive charges from Fe majority d-states to unoccupied Gd f-minority states with f-electron character excited occupation lagging behind that of the d-electron character, leading to substantial demagnetization of both species while leaving the global moment almost unchanged. For x > 0.33, this results in the creation of an ultrafast ferromagnetic (FM) transient by the end of the laser pulse with the Gd demagnetization rate slower than that of Fe. For all concentrations, the Gd moments begin to rotate from their ground state orientations developing in-plane moments of between 0.2 and 0.5 μB. Thus, the ultrafast spin dynamics of the material captures three important ingredients of all optical switching that occurs at much later (picosecond) times: (i) the development of a FM transient, (ii) the different rates of demagnetization of Fe and Gd, and (iii) the breaking of the collinear symmetry of the ground state. Furthermore, several predictions are made about the behavior of Fe-Gd alloys that can be experimentally tested and can lead to a spin-filtering device