Hemophagocytic lymphohistiocytosis associated with an IgG Cold agglutinin.

Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening disease eventually caused or reactivated by a viral infection, which can also lead to the production of cold agglutinins (CA). The nature of these autoantibodies is usually an IgM, less frequently an IgA or IgG, they agglutinate red blood cells at low temperatures. They can interfere with hematological parameters causing interpretation difficulties. We report a case of a 4-year-old boy who developed an IgG CA during recurrent HLH reactivated by EBV infection. The purpose of this observation is to underline HLH criteria and to analyze CA interference as well as its biological and clinical characteristics.

Real-space imaging of non-collinear antiferromagnetic order with a single-spin magnetometer.

Although ferromagnets have many applications, their large magnetization and the resulting energy cost for switching magnetic moments bring into question their suitability for reliable low-power spintronic devices. Non-collinear antiferromagnetic systems do not suffer from this problem, and often have extra functionalities: non-collinear spin order may break space-inversion symmetry and thus allow electric-field control of magnetism, or may produce emergent spin-orbit effects that enable efficient spin-charge interconversion. To harness these traits for next-generation spintronics, the nanoscale control and imaging capabilities that are now routine for ferromagnets must be developed for antiferromagnetic systems. Here, using a non-invasive, scanning single-spin magnetometer based on a nitrogen-vacancy defect in diamond, we demonstrate real-space visualization of non-collinear antiferromagnetic order in a magnetic thin film at room temperature. We image the spin cycloid of a multiferroic bismuth ferrite (BiFeO3) thin film and extract a period of about 70 nanometres, consistent with values determined by macroscopic diffraction. In addition, we take advantage of the magnetoelectric coupling present in BiFeO3 to manipulate the cycloid propagation direction by an electric field. Besides highlighting the potential of nitrogen-vacancy magnetometry for imaging complex antiferromagnetic orders at the nanoscale, these results demonstrate how BiFeO3 can be used in the design of reconfigurable nanoscale spin textures.