Magnetic Transitions in Samarium at High Pressures and Low Temperatures

Undergraduate #335
Discipline: Physics
Subcategory: Materials Science

Craig Johnson - Saint Augustine's University
Co-Author(s): Yogesh K.Vohra and Georgiy Tsoi, University of Alabama at Birmingham

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The magnetic transitions in rare-earth metal Samarium have been studied up to 40 GPa and 10 K in a diamond anvil cell. The rare-earth metal Samarium is known to undergo structural phase transitions from Samarium phase to double hexagonal close packed phase at 1 GPa to face centered cubic phase at 14 GPa with increasing pressure. We employ designer diamond technology to measure electrical resistance changes at magnetic transitions under high pressures and low temperatures. The diamond anvil cell was cooled to 10 K using a Cryomech cooler and the pressure was measured by ruby fluorescence technique. Electrical resistance was measured at high pressures and low temperatures by the use of the four probe technique. We track the two known magnetic phase transitions temperatures (Neel temperatures) in Samarium to high pressures observed through electrical transport. A merging of Neel transition temperatures was found within the double hexagonal close packed phase at 12.2 GPa. The magnetic transition temperatures show a correlation with the underlying structural phase transitions between the hexagonal close packed layered structures. The magnetic transition persists up to the highest pressure of 40 GPa achieved in the present experiments. The present study provides information on the changes in the magnetic ordering temperatures and electronic structures induced by high pressures.

Funder Acknowledgement(s): NSF Research Experience for Undergraduates (REU) under Award Number: DMR-1460392. University of Alabama at Birmingham.

Faculty Advisor: Yogesh K. Vohra, ykvohra@uab.edu

Role: High pressure low temperature experiments were performed by use of a cryogenic device. The first step of the experiment would involve samarium as a sample test subject. Samarium was loaded into a cryogenic compressor placed between two diamond anvil cells. Within the cryogenic device temperature and pressure would be altered from 300K down to 10K with a range of pressure of 1.8 GPa to 38.6 GPa. Measurements of resistance, temperature, and pressure were recorded using Virtual instruments programming. Pressure was measured manually with the use of the VI and a ruby florescent light emitted by a 200 m(W) laser which was replaced with a 300 m(W) up to 40 GPa. In order to collect pressure measurements from the ruby fluorescents a camera would intake the amount of light emitted from the ruby.