Interpretation of the giant magnetoresistance effect in Co/Cu(100) multilayers with the quantum model of giant magnetoresistance

\u3cp\u3eWe have measured the magnetoresistance of high-vacuum-sputtered Co/Cu(100) multilayers grown on Cu buffer layers. The magnetoresistance in the first antiferromagnetic- (AF-) coupling peak is very sensitive to the buffer layer thickness. We find a linear dependence between the actual measured magnetoresistance and the fraction of AF coupling, as determined by magnetization measurements. We compare our Co/Cu(100) magnetoresistance data at 4 K of completely antiparallel-aligned multilayers with the quantum model of giant magnetoresistance of Levy, Zhang, and Fert. This reveals evidence for strong spin-dependent interface scattering, whereas the spin dependence of the bulk scattering in Co is small.\u3c/p\u3

Determination of spin-dependent scattering parameters of NiFe/Cu and Co/Cu multilayers

We present magnetoresistance (MR) data of high-vacuum magnetron sputtered NiFe/Cu multilayers (NiFe=NisoFe20) grown on Si(lOO) substrates with a Cu buffer layer and compare these with earlier results on Co/Cu(lOO) multilayers [1]. Measured MR values are directly proportional to the antiferromagnetically coupled fraction in the multilayers. Extrapolating to full antiparallel alignment, we can make a reliable comparison of the MR wrt,h the magnetoresistance model of Levy,\u3cbr/\u3eZhang, and Fert [2,3]. For the NiFe/Cu multilayers the deduced spin-asymmetry parameters are a~iFe/Cu = 5.0 ± 0.4 and a~iFe = 2.1 ± 0.3 for interface and bulk scattering, respectively. Although much smaller than in our Co/Cu multilayers, where afo/Cu = 21 ± 3 and af0 = 2.6 ± 0.3, .it is still the spin dependence of the interface scattering that is the main cause for the large MR values

Identifying growth mechanisms for laser-induced magnetization in FeRh

Time-resolved pump-probe measurements of the magnetic phase change from paramagnetic to ferromagnetic and back in FeRh thin films are presented. Data are compared with simulations of laser-induced magnetization dynamics using the Landau-Lifshitz-Gilbert equation with a time dependent magnetization d., responding to the evolution of the thermal profile throughout the film. The obsd. magneto-optical transients should be interpreted in terms of an interplay between the local magnetic moment, nonlocal domain growth or alignment, and magnetization precession as launched by the varying demagnetizing fields. Kerr rotation and reflectivity provide a complementary view on the phase transition. [on SciFinder (R)

1/f noise in anisotropic and giant magnetoresistive elements

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a 1/f contribution that depends on the applied magnetic field. The 1/f noise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The 1/f noise level observed in saturation is comparable to the 1/f noise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction

Quantum well states in spin-dependent tunnel structures

The magnetotransport behavior of magnetic tunnel junctions with a nonmagnetic interface layer has been studied. The initial effect of the added layer is to reduce the magnetoresistance effect. Also, the bias voltage dependence of the magnetoresistance becomes increasingly more asymmetric. The dependence of the magnetoresistance both on the thickness of the interface layer as well as on the bias voltage can be interpreted as signatures of the development of quantum well states

Magnetite Fe3-deltaO4 : a stoichiometry and structure analysis of MBE grown thin films using NO2 as the oxidising source

Epitaxial single crystalline films of iron oxides have been grown on MgO(100) substrates by means of MBE. Natural Fe or 57Fe was evaporated from alumina crucibles, and oxidised simultaneously with a dosed flux of NO2. The resulting oxide layers have been characterised in situ with RHEED, LEED, XPS, and AES. RHEED intensity oscillations, observed during deposition of the oxides, indicate a layer-by-layer growth for all substrate temperatures between 373 and 673 K. A stoichiometry analysis with CEMS, performed ex situ, shows that it is straightforward to prepare both the stable magnetite Fe3O4 and the metastable maghemite Fe3-dO4 phases. Moreover, also al1 solid solutions in between these two extreme phases, i.e. Fe3-dO4 with

On the construction of an Fe3O4 based all-oxide spin-valve

The progress made in constructing an all-oxide spin valve based on the intrinsic, fully spin-polarized electron transport in Fe3O4 is discussed. Two possible oxidic spacer layers, MgO and Mn3O4, have been investigated. Interlayer coupling studies indicate that MgO is the more suitable spacer layer of the two. Thus far a limited magnetoresistive effect 0.4% is found in the all oxide, Fe3O4-based, spin-valves which we have made. Possible causes for this low magnetoresistive effect are discussed

Taskforce report on the diagnosis and clinical management of COVID-19 associated pulmonary aspergillosis.

Invasive pulmonary aspergillosis (IPA) is increasingly reported in patients with severe coronavirus disease 2019 (COVID-19) admitted to the intensive care unit (ICU). Diagnosis and management of COVID-19 associated pulmonary aspergillosis (CAPA) are challenging and our aim was to develop practical guidance. A group of 28 international experts reviewed current insights in the epidemiology, diagnosis and management of CAPA and developed recommendations using GRADE methodology. The prevalence of CAPA varied between 0 and 33%, which may be partly due to variable case definitions, but likely represents true variation. Bronchoscopy and bronchoalveolar lavage (BAL) remain the cornerstone of CAPA diagnosis, allowing for diagnosis of invasive Aspergillus tracheobronchitis and collection of the best validated specimen for Aspergillus diagnostics. Most patients diagnosed with CAPA lack traditional host factors, but pre-existing structural lung disease and immunomodulating therapy may predispose to CAPA risk. Computed tomography seems to be of limited value to rule CAPA in or out, and serum biomarkers are negative in 85% of patients. As the mortality of CAPA is around 50%, antifungal therapy is recommended for BAL positive patients, but the decision to treat depends on the patients' clinical condition and the institutional incidence of CAPA. We recommend against routinely stopping concomitant corticosteroid or IL-6 blocking therapy in CAPA patients. CAPA is a complex disease involving a continuum of respiratory colonization, tissue invasion and angioinvasive disease. Knowledge gaps including true epidemiology, optimal diagnostic work-up, management strategies and role of host-directed therapy require further study

Review of influenza-associated pulmonary aspergillosis in ICU patients and proposal for a case definition: an expert opinion.

Invasive pulmonary aspergillosis is increasingly reported in patients with influenza admitted to the intensive care unit (ICU). Classification of patients with influenza-associated pulmonary aspergillosis (IAPA) using the current definitions for invasive fungal diseases has proven difficult, and our aim was to develop case definitions for IAPA that can facilitate clinical studies. A group of 29 international experts reviewed current insights into the epidemiology, diagnosis and management of IAPA and proposed a case definition of IAPA through a process of informal consensus. Since IAPA may develop in a wide range of hosts, an entry criterion was proposed and not host factors. The entry criterion was defined as a patient requiring ICU admission for respiratory distress with a positive influenza test temporally related to ICU admission. In addition, proven IAPA required histological evidence of invasive septate hyphae and mycological evidence for Aspergillus. Probable IAPA required the detection of galactomannan or positive Aspergillus culture in bronchoalveolar lavage (BAL) or serum with pulmonary infiltrates or a positive culture in upper respiratory samples with bronchoscopic evidence for tracheobronchitis or cavitating pulmonary infiltrates of recent onset. The IAPA case definitions may be useful to classify patients with COVID-19-associated pulmonary aspergillosis (CAPA), while awaiting further studies that provide more insight into the interaction between Aspergillus and the SARS-CoV-2-infected lung. A consensus case definition of IAPA is proposed, which will facilitate research into the epidemiology, diagnosis and management of this emerging acute and severe Aspergillus disease, and may be of use to study CAPA