Annika and Andrew join as REU students

Annika Lagy uses electron paramagnetic resonance (EPR) spectroscopy to characterize the differences between a group of five Ni samples with different ligands. Each Ni sample is ground into a fine powder and placed in the center of a magnet where it is irradiated with microwaves. Due to the Zeeman effect, when a magnetic field is applied, the spin states of unpaired electrons in the Ni become non-degenerate and the difference in energy between them increases linearly with the magnetic field. There is a particular magnetic field value where this energy difference is in resonance, or proportional to the microwave frequency, allowing the electrons to be excited to a different spin state. In EPR, the magnetic field is swept at a constant microwave frequency and an absorption spectrum is recorded to detect when these excitations occur. Due to the large zero-field splitting in the Ni samples and the restriction of using frequencies below 600 GHz in EPR, we are primarily observing the parallel mode transitions between the +1 and -1 spin states.

Andrew Cook studies single-crystal samples that are mounted onto a probe capable of in situ two-axis sample rotation. The probe is then loaded into the center of a horizontal-field, split-pair magnet encased in a cryogenic chamber. The special electron configuration of interesting samples allow for unpaired electrons to be studied using this experimental setup. There are multiple EPR detection schemes, the method we use is just one of these. With our method, Microwave frequencies are generated, sent to the sample, retrieved, analyzed, and compared, using a custom network of electronics. Excitations in the unpaired electrons can be inferred through these signals. The excitation from one energy level to another in the presence of a magnetic field, known as resonance, is of focus to my cohort. On top of differences due to electronic structure, differing the values for the orientation of the sample, microwave frequency, chamber temperature and magnetic field strength all have an effect on how a resonance occurs. EPR has various applications in Quantum Information/Computing, Chemistry, and Biology.