Absence of halfmetallicity in defect-free Cr, Mn-delta-doped Digital Magnetic Heterostructures

We present results of a combined density functional and many-body calculations for the electronic and magnetic properties of the defect-free digital ferromagnetic heterostructures obtained by doping GaAs with Cr and Mn. While local density approximation/(+U) predicts half-metallicity in these defect-free delta-doped heterostructures, we demonstrate that local many-body correlations captured by Dynamical Mean Field Theory induce within the minority spin channel non-quasiparticle states just above $E_F$. As a consequence of the existence of these many-body states the half-metallic gap is closed and the carriers spin polarization is significantly reduced. Below the Fermi level the minority spin highest valence states are found to localize more on the GaAs layers being independent of the type of electronic correlations considered. Thus, our results confirm the confinement of carriers in these delta-doped heterostructures, having a spin-polarization that follow a different temperature dependence than magnetization. We suggest that polarized hot-electron photoluminescence experiments might bring evidence for the existence of many-body states within the minority spin channel and their finite temperature behavior.Comment: 10 pages 8 figures, submitted to PR

Observation and theoretical description of the pure Fano-effect in the valence-band photo-emission of ferromagnets

The pure Fano-effect in angle-integrated valence-band photo-emission of ferromagnets has been observed for the first time. A contribution of the intrinsic spin polarization to the spin polarization of the photo-electrons has been avoided by an appropriate choice of the experimental parameters. The theoretical description of the resulting spectra reveals a complete analogy to the Fano-effect observed before for paramagnetic transition metals. While the theoretical photo-current and spin difference spectra are found in good quantitative agreement with experiment in the case of Fe and Co only a qualitative agreement could be achieved in the case of Ni by calculations on the basis of plain local spin density approximation (LSDA). Agreement with experimental data could be improved in this case in a very substantial way by a treatment of correlation effects on the basis of dynamical mean field theory (DMFT).Comment: 11 pages, 3 figures accepted by PR

Magnetic transitions in alpha-Fe_2O_3 nanowires

Magnetic transitions in single-crystal alpha-F_2O_3 (hematite) nanowires, grown by thermal oxidation of iron powder, have been studied in the range of 5-1023 K with a superconducting quantum interference device below room temperature and with a vibrating sample magnetometer at higher temperatures. The broad temperature range covered enables us to compare magnetic transitions in the nanowires with the transitions reported for bulk hematite. Morin temperatures (T-M) of the nanowires and of hematite bulk reference powder were found to be 123 and 263 K, respectively. Also the Neel temperature (T-N) of the nanowires, 852 K, was lower than the bulk T-N value. Measurements of the magnetization as a function of temperature show an enhanced signal in the nanowires, which suggests a decrease in the anti ferromagnetic coupling. A coercive field observed below T-M in the hysteresis loops of the nanowires is tentatively explained by the presence of a magnetic phase

De Haas-van Alphen effect and Fermi surface properties of single crystal CrB2

We report the angular dependence of three distinct de Haas-van Alphen (dHvA) frequencies of the torque magnetization in the itinerant antiferromagnet CrB2 at temperatures down to 0.3K and magnetic fields up to 14T. Comparison with the calculated Fermi surface of nonmagnetic CrB2 suggests that two of the observed dHvA oscillations arise from electron-like Fermi surface sheets formed by bands with strong B-px,y character which should be rather insensitive to exchange splitting. The measured effective masses of these Fermi surface sheets display strong enhancements of up to a factor of two over the calculated band masses which we attribute to electron-phonon coupling and electronic correlations. For the temperature and field range studied, we do not observe signatures reminiscent of the heavy d-electron bands expected for antiferromagnetic CrB2. In view that the B-p bands are at the heart of conventional high-temperature superconductivity in the isostructural MgB2, we consider possible implications of our findings for nonmagnetic CrB2 and an interplay of itinerant antiferromagnetism with superconductivity.Comment: 8 pages, 4 figure

Heart failure during the COVID-19 pandemic: clinical, diagnostic, management, and organizational dilemmas

The coronavirus 2019 (COVID-19) infection pandemic has affected the care of patients with heart failure (HF). Several consensus documents describe the appropriate diagnostic algorithm and treatment approach for patients with HF and associated COVID-19 infection. However, few questions about the mechanisms by which COVID can exacerbate HF in patients with high-risk (Stage B) or symptomatic HF (Stage C) remain unanswered. Therefore, the type of HF occurring during infection is poorly investigated. The diagnostic differentiation and management should be focused on the identification of the HF phenotype, underlying causes, and subsequent tailored therapy. In this framework, the relationship existing between COVID and onset of acute decompensated HF, isolated right HF, and cardiogenic shock is questioned, and the specific management is mainly based on local hospital organization rather than a standardized model. Similarly, some specific populations such as advanced HF, heart transplant, patients with left ventricular assist device (LVAD), or valve disease remain under investigated. In this systematic review, we examine recent advances regarding the relationships between HF and COVID-19 pandemic with respect to epidemiology, pathogenetic mechanisms, and differential diagnosis. Also, according to the recent HF guidelines definition, we highlight different clinical profile identification, pointing out the main concerns in understudied HF populations.© 2022 The Authors. ESC Heart Failure published by John Wiley & Sons Ltd on behalf of European Society of Cardiology

Nonquasiparticle states in half-metallic ferromagnets

Anomalous magnetic and electronic properties of the half-metallic ferromagnets (HMF) have been discussed. The general conception of the HMF electronic structure which take into account the most important correlation effects from electron-magnon interactions, in particular, the spin-polaron effects, is presented. Special attention is paid to the so called non-quasiparticle (NQP) or incoherent states which are present in the gap near the Fermi level and can give considerable contributions to thermodynamic and transport properties. Prospects of experimental observation of the NQP states in core-level spectroscopy is discussed. Special features of transport properties of the HMF which are connected with the absence of one-magnon spin-flip scattering processes are investigated. The temperature and magnetic field dependences of resistivity in various regimes are calculated. It is shown that the NQP states can give a dominate contribution to the temperature dependence of the impurity-induced resistivity and in the tunnel junction conductivity. First principle calculations of the NQP-states for the prototype half-metallic material NiMnSb within the local-density approximation plus dynamical mean field theory (LDA+DMFT) are presented.Comment: 27 pages, 9 figures, Proceedings of Berlin/Wandlitz workshop 2004; Local-Moment Ferromagnets. Unique Properties for Moder Applications, ed. M. Donath, W.Nolting, Springer, Berlin, 200

The effect of the spin-orbit interaction on the band gap of half-metals

The spin-orbit interaction can cause a nonvanishing density of states (DOS) within the minority-spin band gap of half-metals around the Fermi level. We examine the magnitude of the effect in Heusler alloys, zinc-blende half metals and diluted magnetic semiconductors, using first-principles calculations. We find that the ratio of spin-down to spin-up DOS at the Fermi level can range from below 1% (e.g. 0.5% for NiMnSb) over several percents (4.2% for (Ga,Mn)As) to 13% for MnBi.Comment: 5 pages, 3 figure