Measuring magnetic field strength using velocity gradient

Prof. Alex Lazarian
Department of Astronomy, University of Wisconsin-Madison

Magnetic field measurements using dust polarization and spectral line widths is known as Chandrasekhar-Fermi technique. This technique is widely used for studying magnetic fields in interstellar media. I will discuss first the new technique that can provide higher accuracy using less amount of polarization and spectral line data. Then I will discuss how to obtain magnetic field strength without polarization information and also in the situations when the traditional technique is not applicable. Finally, I will discuss how to get the 3D distribution of magnetic field strength in the interstellar medium.…

Measuring topological stability of magnetic skyrmions

Allan Leishman, Physics Graduate Student
University of Notre Dame

Magnetic skyrmions show promise for future data storage applications due to their small size and observation at a wide range of temperatures and magnetic fields.  Key to their surprising stability is a topological energy barrier which must be overcome to create or destroy a skyrmion in a magnetic material.  Understanding the nature of this energy barrier and how to maximize it is essential to the longstanding goal of building nanoscale skyrmion devices at room temperature and zero applied field. We have developed a novel method for measuring the topological energy barrier of skyrmion lattices (SkL) and have used it to characterize the prototypical skyrmion hosting material MnSi. Using small angle neutron scattering (SANS) we have observed a small hysteresis associated with entering and leaving the SkL phase. By modelling this hysteresis with an adapted Preisach free energy curve, we can extract the SkL energy barrier and infer information about the microscopic details of the phase transition.  Combining our SANS result  with atomistic spin simulations, we conclude  that the SkL forms progressively in domains which are hundreds of nanometers in size. In this seminar I will discuss the fundamentals of magnetic skyrmion lattices, motivate why SANS is an excellent technique to study skyrmions, and outline our recent findings in MnSi.…

The famous saying, “numbers don’t lie,” might work when reporting the score of a football game, but even then, the numbers don’t tell the whole story. 

Algorithms developed by data scientists have implications for not only who may obtain a fair loan, but with who stays in prison and who’s released, and who will be favored by machine learning “decisions.” With so many parts of our lives decided by Big Data, how do scientists balance the algorithms and the ethics?…

Neutron transfer and neutron capture on the example of ²⁵Mg(d,p) and ²⁵Mg(n,g)

Dr. Joachim Goerres
Department of Physics, University of Notre Dame

Radiative neutron capture reactions play an important role in nuclear astrophysics. In some cases direct neutron capture reaction studies are not possible and neutron transfer reactions have been suggested as a…

Title TBA

Michelle Berg
Physics Graduate Student
University of Notre Dame…