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Date of Award
Doctor of Philosophy (PhD)
Lanthanides are of particular interest because of the highly localized nature of their 4f electrons. Under sufficiently high pressure we can anticipate that the 4f state of a given lanthanide becomes unstable, leading to highly correlated electron effects and exotic physics. The main goal of this dissertation is to destabilize the 4f state in selected lanthanides through extreme pressure using diamond anvil cell (DAC) technology and search for anomalous magnetic and superconducting properties.
Four-point electrical resistivity measurements on Nd metal to 2 Mbar pressure reveal that its magnetic ordering temperature To soars to anomalously high values, in analogy with earlier results on the lanthanide Dy. In addition, giant superconducting pair-breaking and resistivity minima are observed in the dilute magnetic alloy Y(Nd) revealing the presence of exotic Kondo effect phenomena that may, in fact, be responsible for the anomalously high values of To. High pressure studies using synchrotron Mössbauer spectroscopy on Dy confirm the magnetic origin of the transitions detected by electrical resistivity, giving further support to the Kondo physics scenario.
Trivalent Pr has a crystal-field-split singlet ground state that leads to magnetic ordering at temperatures well below 1 K. Applying pressure is a promising way to tune Pr's ground state and possibly significantly enhance the ordering temperature. Although there is no evidence for magnetic ordering in Pr in the temperature range 1.5 - 295 K to 48 GPa, Pr in the dilute magnetic Y(Pr) alloy exhibits Kondo effect phenomena as evidenced by the "sink-hole" shape of the pair breaking curve.
Unlike most lanthanides at ambient pressure, Yb does not order magnetically since divalent Yb is magnetically inert with a completely filled 4f14 orbital. Applying extreme pressure can significantly transform both the electronic and crystal structure of materials and thus possibly induce magnetic ordering or superconductivity in Yb. According to a previous report, Yb suffers an increase in valence under pressure. If so, each Yb ion would possess a strong local magnetic moment that would be expected to lead to magnetic ordering in the temperature range above 1 K according to de Gennes scaling. However, no evidence for magnetic ordering in Yb is found from 1.4 to 295 K to 180 GPa. Of particular significance is the discovery that Yb becomes superconducting above 86 GPa at 1.4 K for pressures exceeding 86 GPa, as evidenced by electrical resistivity and ac magnetic susceptibility measurements.
Chair and Committee
James S. Schilling
James S. Schilling, Sophia E. Hayes, Erik A. Henriksen, Anne M. Hofmeister,
Song, Jing, "Highly Correlated Electron Effects in Selected Lanthanides under Extreme Pressure" (2018). Arts & Sciences Electronic Theses and Dissertations. 1585.
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