Evolution of interlayer and intralayer magnetism in three atomically thin chromium trihalides.

We conduct a comprehensive study of three different magnetic semiconductors, CrI3, CrBr3, and CrCl3, by incorporating both few-layer and bilayer samples in van der Waals tunnel junctions. We find that the interlayer magnetic ordering, exchange gap, magnetic anisotropy, and magnon excitations evolve systematically with changing halogen atom. By fitting to a spin wave theory that accounts for nearest-neighbor exchange interactions, we are able to further determine a simple spin Hamiltonian describing all three systems. These results extend the 2D magnetism platform to Ising, Heisenberg, and XY spin classes in a single material family. Using magneto-optical measurements, we additionally demonstrate that ferromagnetism can be stabilized down to monolayer in more isotropic CrBr3, with transition temperature still close to that of the bulk.

The use of black and white infrared photography for recording blunt force injury.

Infrared (IR) wavelengths penetrate skin and can selectively image volumes of subsurface blood. Twenty-eight blunt force injuries on nine decedents were photographed with color and IR film to compare the ability of each to image the injury. Of the 28 injuries, 10 were clinically interpreted as contusions, 4 as abrasions, 10 as abraded contusions, and 4 as erythematous discolorations, nos. Twenty-four of these injuries were incised to determine the presence and extent of subsurface bleeding. It was found that contusion had been clinically missed in five cases, three because they were hidden by abrasion and two because they appeared only as a mild cutaneous erythema. All five cases were detected by IR and verified by incision. Melanin pigmentation contributed to masking of contusion in one case and postmortem lividity confounded interpretation of contusion in one case. In all 14 injuries featuring abrasion as a component, IR de-emphasized or eliminated the visibility of abrasion. A single false negative was reported in which a visible contusion, verified by incision, was not seen with IR. In comparing injury patterns, color and IR renditions were dissimilar in a number of cases reflecting the difference between the manner in which light and IR photography imaged the depth and volume of blood within an injury. In summary, IR imaging of wounds can discover hidden bruises, verify clinical diagnosis of bruises, and augment interpretation of wound patterns.