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Kush, Dhruv

University of British Columbia

Considerably more experimental and theoretical progress has been made in studying local moment magnets compared to itinerant magnets, systems where magnetic moment carriers are delocalized throughout the crystal lattice. Progress is hindered by the small number of known itinerant magnets, difficulties in synthesis, and small moment sizes. In this thesis, we study itinerant magnetism in the intermetallic compound ZrZn₂. Presumed to order ferromagnetically, recent evidence from the local probes of muon spin relaxation (μSR) and time dependent perturbed angular correlation (TDPAC) suggests ZrZn₂’s ordered phase is a more complex magnetic ordering. We find that polycrystalline ZrZn₂ is best synthesized through solid state reaction at reaction temperatures below 700 °C. Impurity phase percentages are found to increase with temperature, with ZrZn₃ being the dominant impurity above 800 °C. Bulk magnetization measurements reveal ZrZn₂ is an unsaturated magnet up to 7T, with a saturated moment size 0.18 μB/f.u. We find saturated moment sizes at 2K, in external fields, are only 10% of free moment sizes obtained from Curie-Weiss like fits to the magnetic susceptibility. Furthermore, Knight shift measurements show the zero field ordered moment corresponding to simple ferromagnetic ordering is only 4% of the free moment. As this is suggestive of geometric moment cancellations in the ordered phase of ZrZn₂, we employ μSR to probe its magnetic ordering in zero field (ZF) and dynamical processes contributing to this ordering in longitudinal field (LF). ZF μSR spectra displays oscillations in the ordered phase (below 15.5K) that are more damped than the only previous report in literature, hinting at inhomogeneities in the measured sample. In the LF geometry, we find non-zero residual relaxation rates in ZrZn₂ persist up to 2K, which is atypical of simple ferromagnets. We conclude that while the temperature dependence of LF relaxation rates above 15.5K and inverse magnetic susceptibility in the paramagnetic regime agrees with the self consistent renormalization theory (SCR) for itinerant ferromagnets, a large difference in ordered and free moment size and non-zero LF relaxation rates up to 2K are suggestive of magnetic ordering more complex than simple ferromagnetism in ZrZn₂.

Text

2023-08-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/85693

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/