Magnetic Compensation in the Bimetallic Oxalates and the Cerium Volume Collapse

• Main Author: Reis, Peter Leo
• Other Authors: Moreno Juana
• Format: Others
• Language: en
• Published: LSU 2012
• Subjects: Physics & Astronomy
• Online Access: http://etd.lsu.edu/docs/available/etd-08172012-134340/

In this thesis the author reports his collaborative efforts on two distinct areas of research that has been conducted. The first part of the thesis pertains to the author and his collaborators research on a particular class of organic magnets called the bimetallic oxalates. The main theme of this research was to predict magnetic compensation (magnetization reversal) in unsynthesized bimetallic oxalate structures, motivated by experiments which showed that Fe(II)Fe(III) exhibited magnetic compensation. In addition it was known that a large amount of anisotropy was present in the bimetallic oxalate structure which resulted from the intermediate oxalate molecules between the transition metal ions which would drastically change the angular momentum of the transition metals. Consequently, because of the large anisotropy, we predicted that, if neutron diffraction measurements were performed on these materials, a spin-wave gap would exist of the order of 7.8 meV. The second half of this thesis is devoted to the author's and his collaborators' research on the cerium volume collapse. Until 2004 the collapse was largely believed to be understood as the result of Kondo screening of the local moment in cerium. However in 2004 it was realized that, in addition to a large Kondo effect driving the cerium volume collapse, the phonon frequency was very different between the large and small volume phases, and consequently the change in phonon frequency was the direct result of large electron-phonon correlations. This upset the apple cart of Kondo correlation being solely responsible for the volume collapse in cerium, and the change in phonon frequency must be accounted for to accurately describe the cerium volume collapse. To this end the author and his collaborators' developed a model which would include both of the correlations (Kondo and phononic) in the volume collapse. To analyze this model we used Dynamical Mean Field Theory in conjunction with Continuous Time Quantum Monte Carlo. What we found in our simulations was that the small volume Kondo phase was drastically influenced by the presence of the electron-phonon correlations.