Time-resolved ferromagnetic resonance in epitaxial Fe1-xCox films

Magnetodynamics in epitaxial Fe1-xCox films on GaAs (100) are studied using time-resolved ferromagnetic resonance, in which the free precession of the magnetization after an impulsive excitation is measured using the polar Kerr effect. The sample is rotated with respect to the static and pulsed field directions, providing a complete mapping of the free energy surface and characteristic relaxation times. The magnetic response can be simulated with a simple coherent rotation model except in the immediate vicinity of switching fields. Bulk and surface anisotropies are identified, and unusual dynamics associated with the coexistence of cubic and uniaxial anisotropies are observed.Comment: PDF - 4 figure

Scanning probe metrology in the presence of surface charge

Surface charge on insulating samples can be a significant source of error for scanning probe microscopes. We have found that it is possible to operate a scanning force microscope in a manner that makes it relatively immune to charge-induced forces while still allowing the probe tip to nondestructively follow the surface topography. The need to maintain close charge balance on the sample is thus obviated. We have used this strategy to perform critical dimension measurements on optical photomasks with the Surface/Interface Stylus NanoProfilometer. This instrument incorporates a servoed force-balance sensor. Surface topography is determined by touching the surface with contact forces between 0.1 and 1 muN. (C) 2000 American Vacuum Society. [S0734-211X(00)01706-6]

Optical determination of the Néel vector in a CuMnAs thin-film antiferromagnet

Recent breakthroughs in electrical detection and manipulation of antiferromagnets have opened a new avenue in the research of non-volatile spintronic devices.1-10 Antiparallel spin sublattices in antiferromagnets, producing zero dipolar fields, lead to the insensitivity to magnetic field perturbations, multi-level stability, ultrafast spin dynamics and other favorable characteristics which may find utility in fields ranging from magnetic memories to optical signal processing. However, the absence of a net magnetic moment and the ultra-short magnetization dynamics timescales make antiferromagnets notoriously difficult to study by common magnetometers or magnetic resonance techniques. In this paper we demonstrate the experimental determination of the Néel vector in a thin film of antiferromagnetic CuMnAs9,10 which is the prominent material used in the first realization of antiferromagnetic memory chips.10 We employ a femtosecond pump-probe magneto-optical experiment based on magnetic linear dichroism. This table-top optical method is considerably more accessible than the traditionally employed large scale facility techniques like neutron diffraction11 and Xray magnetic dichroism measurements.12-14 This optical technique allows an unambiguous direct determination of the Néel vector orientation in thin antiferromagnetic films utilized in devices directly from measured data without fitting to a theoretical model

Spin-Dependent Transport in Fe/GaAs(100)/Fe Vertical Spin-Valves

The integration of magnetic materials with semiconductors will lead to the development of the next spintronics devices such as spin field effect transistor (SFET), which is capable of both data storage and processing. While the fabrication and transport studies of lateral SFET have attracted greatly attentions, there are only few studies of vertical devices, which may offer the opportunity for the future three-dimensional integration. Here, we provide evidence of two-terminal electrical spin injection and detection in Fe/GaAs/Fe vertical spin-valves (SVs) with the GaAs layer of 50 nanometers thick and top and bottom Fe electrodes deposited by molecular beam epitaxy. The spin-valve effect, which corresponds to the individual switching of the top and bottom Fe layers, is bias dependent and observed up to 20 K. We propose that the strongly bias-and temperature-dependent MR is associated with spin transport at the interfacial Fe/GaAs Schottky contacts and in the GaAs membranes, where balance between the barrier profiles as well as the dwell time to spin lifetime ratio are crucial factors for determining the device operations. The demonstration of the fabrication and spin injection in the vertical SV with a semiconductor interlayer is expected to open a new avenue in exploring the SFET

What do ‘false-positive’ stool tests really mean? Data from the New Hampshire colonoscopy registry

We utilized the population-based New Hampshire Colonoscopy Registry to calculate false discovery rates (FDR) and positive predictive values (PPVs) using three ‘positive’ colonoscopy definitions. Understanding the frequency of meaningful ‘true positive’ mt-sDNA and Fecal Immunochemical Test (FIT) results can optimize the use of these colorectal cancer (CRC) screening tests. We calculated FDR (positive stool test followed by negative colonoscopy divided by all positive stool tests) and PPV for mt-sDNA and FIT cohorts using the following definitions:1) DeeP-C Study (CRC, adenomas/serrated polyps ≥ 1 cm, villous/High Grade Dysplasia);2)  1 cm, and 5–9 mm proximal HPs.The sample included 549 mt-sDNA + and 410 FIT + and patients (mean age 66.4, 43.0% male). Using the most limited definition of positive colonoscopy, DeeP-C, FDR was 71.9% for mt-sDNA + and 81.7% for FIT +. Using the USMSTF definition, FDR decreased substantially: mt-sDNA+:33.2% and FIT+:47.6%. Adding all CSSPs resulted in the lowest FDR: mt-sDNA+:32.2% and FIT+:47.1%. Decreasing FDRs corresponded to increasing PPVs: mt-sDNA+:28.1% and FIT+:18.3% (DeeP-C definition) and mt-sDNA+:67.8% and FIT+:52.9% (DeeP-C + USMSTF + CSSP) (Table 1).FDRs decreased substantially when the definition of positive exams included all significant precancerous findings. These data present a comprehensive understanding of false positive outcomes at colonoscopies following positive stool tests, which to our knowledge is the first such analysis