Graduation Semester and Year

2008

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Physics and Applied Physics

Department

Physics

First Advisor

Ali R Koymen

Abstract

Multilayers of Co/Tb, Ni/Gd, NiFe/Gd, CoFe/Gd and CoNi/Gd multilayers have been synthesized using dc magnetron sputtering and have been investigated experimentally by SQUID magnetometry. Due to the antiferromagnetic coupling between the transition metal and rare earth layers these systems behave like artificial ferrimagnets, with a minimum in total magnetic moment at compensation temperature. The measurement of magnetic moment (M) as a function of temperature (T) shows that magnetic phase transition occurs at different temperatures during the heating (superheating) and cooling (supercooling) cycles resulting in thermal hysteresis curve for M (T). Magnetic entropy change has been measured for CoFe/Gd and CoNi/Gd nanolayers. ∆S (T) associated with first order magnetic phase transitions, has a minimum during the cooling cycle and a maximum during the heating cycle. The magnetic phase transitions with entropy change can be controlled over 20-300K interval with small applied magnetic fields. The order-order magnetic phase transitions observed in M (T) and ∆S (T) are explained due to the temperature dependence of the Gd moment associated with the existence of an anisotropy field in the transition metal layers. The same multilayer can show none, one, or two-phase transitions by varying an external magnetic field in a small range and by changing the starting point in the cooling/heating cycles.

Disciplines

Physical Sciences and Mathematics | Physics

Comments

Degree granted by The University of Texas at Arlington

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