Dipolar Interactions, Long Range Order and Random Fields in a Single Molecule Magnet, Mn12-acetate

<p>In this thesis, I will present an experimental study of two single molecule magnets, Mn₁₂-ac and Mn₁₂-ac-MeOH. I will show that in both systems, the temperature dependence of the inverse susceptibility yields a positive intercept on the temperature axis (a positive Weiss temperature), implying the existence of a ferromagnetic phase at low temperature.</p> <p>Applying a magnetic field in the transverse direction moves the Weiss temperature downward towards zero. This implies that the transverse field triggers mechanisms in the system that compete with the dipolar interaction and suppress the long-range ordering.</p> <p>I will then show that the suppression in Mn₁₂-ac is considerably stronger than that expected for a pure TFIFM (Transverse Field Ising Ferromagnetic) model system. By contrast, the behavior of Mn₁₂-ac-MeOH is consistent with the model.</p> <p>We attribute the difference between the two systems to the presence of randomness in Mn₁₂-ac associated with isomer disorder. Thus, in addition to spin-canting and thermal fluctuations, which contribute to the suppression of long-range order in both materials in the same way, the random fields due to isomer disorder that exist in Mn₁₂-ac and not in Mn₁₂-ac-MeOH causes further suppression of ferromagnetism in Mn₁₂-ac. The behavior observed for Mn₁₂-ac is consistent with a random field model calculated for this system by Millis et al.</p>

Name thesis:degree_name

Doctor of Philosophy

Level thesis:degree_level

Doctoral

Discipline thesis:degree_discipline

Physics

Grantor

The Graduate School and University Center of The City University of New York

Year dc:date.available

2013

Author dc:creator

• Wen, Bo

Advisor dc:contributor.advisor

• Myriam P. Sarachik

Committee members dc:contributor.committeemember

• Eugene M. Chudnovsky
• Morrel H. Cohen
• Andrew D. Kent
• Sergey Vitkalov

• Physics

Repository record dc:identifier

https://academicworks.cuny.edu/gc_etds/1978

OAI identifier oai:identifier

oai:academicworks.cuny.edu:gc_etds-3007