The Evolution of Sunspot Magnetic Fields Associated with a Solar Flare

Solar flares occur due to the sudden release of energy stored in active-region magnetic fields. To date, the pre-cursors to flaring are still not fully understood, although there is evidence that flaring is related to changes in the topology or complexity of an active region's magnetic field. Here, the evolution of the magnetic field in active region NOAA 10953 was examined using Hinode/SOT-SP data, over a period of 12 hours leading up to and after a GOES B1.0 flare. A number of magnetic-field properties and low-order aspects of magnetic-field topology were extracted from two flux regions that exhibited increased Ca II H emission during the flare. Pre-flare increases in vertical field strength, vertical current density, and inclination angle of ~ 8degrees towards the vertical were observed in flux elements surrounding the primary sunspot. The vertical field strength and current density subsequently decreased in the post-flare state, with the inclination becoming more horizontal by ~7degrees. This behaviour of the field vector may provide a physical basis for future flare forecasting efforts.Comment: Accepted for Publication in Solar Physics. 16 pages, 4 figure

Antiferromagnetic order in Co doped Fe5GeTe2 probed by resonant magnetic x ray scattering

The quasi two dimensional van der Waals magnet Fe5 amp; 8722; amp; 948;GeTe2 has emerged as a promising platform for electronic and spintronic functionalities at room temperature, owing to its large ferromagnetic ordering temperature TC amp; 8776; 315 K. Interestingly, by cobalt Co substitution of iron in F5GT, i.e., Fe1 amp; 8722;xCox 5 amp; 8722; amp; 948;GeTe2 Co F5GT , not only can its magnetic transition temperature be further enhanced, but the magnetic and structural ground states can also be tuned. Specifically, an antiferromagnetic AFM order is induced beyond the Co doping level x amp; 8805;0.4. Here, we investigate the magnetic properties of a Co F5GT single crystal at x 0.45 1 , by utilizing the element specific, resonant magnetic x ray scattering technique. Our study reveals an A type, Ising like AFM ground state, with a transition temperature TN amp; 8776; 340 K. In addition, our work unveils an important contribution from Co magnetic moments to the magnetic order. The application of the in plane magnetic fields gradually polarizes the spin moments along the field direction, but without inducing incommensurate spin texture