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Calendar: ALS Calendar
Title: ALS-CXRO Seminar Series | Chloe Baldasseroni
When: 01/ 9/2013 3:00 PM - 4:00 PM
Description: ALS-CXRO Seminar Series

Wed, January 9, 2013

Peter Fischer/Jinghua Guo

Presented by:
Chloe Baldasseroni
UC Berkeley

Microscopic study of the unusual magnetic phase transition in FeRh thin films

Simple ferromagnetic (FM) and antiferromagnetic (AF) materials such as Fe and Cr become paramagnetic when heated above some critical temperature, in what is known as a second-order phase transition. Less usual magnetic transitions are found in the magnetic world, for example a first-order magnetic phase transition from AF to FM with increasing temperature. Equiatomic FeRh has been known to exhibit such a transition for over 50 years, with a transition temperature slightly above room temperature. Interest in this material has been renewed in the recent years due to its potential application for heat-assisted magnetic recording, as well as a test system for fundamental studies of the physics of magnetic phase transitions. Similarly to a classic first order phase transition such as crystallization, this AF-FM transition is expected to proceed by nucleation of magnetic domains but the features of the first-order hysteretic transition have been difficult to study with macroscopic measurements and very few microscopic studies have been performed.
We used x-ray magnetic dichroism and photoemission electron microscopy to study the temperature-driven AF-FM phase transition in epitaxial FeRh thin films in zero field. Using x-ray magnetic circular dichroism, the different stages of nucleation, growth and coalescence of ferromagnetic domains were observed across the transition. We also found that the FM phase nucleates into single domain islands and the width of the transition of the individual nuclei is sharper than that of the macroscopic transition. Using x-ray magnetic linear dichroism we also performed a similar study of the evolution of the AF phase. Recent results showing differences in the morphology of AF and FM domains will be presented.
Location: 15-253-CR(80)