MSE PhD Proposal: Soo Kyung Kim

Date: Thursday, April 16th, 2015
Time: 11 AM to 3 PM
Location: MRDC 3510

 Committee:

Hamid Garmestani (MSE/Advisor)
Seung Soon Jang (MSE)
Deo, Chaitanya S (ME)
Fujimoto, Richard (CSE)
Benedict, Lorin (External: Lawrence Livermore National Laboratory)

Title:  Thermo-magnetic property of Rare-earth replacement materials using first-principle DFT and Monte-Carlo simulation

Abstract:

Searching for permanent magnet material that is alternative to expensive rare-earth element has gained much attention. Only a material with a large magnetic anisotropic energy and high Currie temperature can perform useful as the rare-earth replacement. In general, problem finding candidate materials should benefit from ab-initio electronic structure calculation and Monte-Carlo simulation, from which Tc and MAE can be predicted. I discuss density functional theory calculation of the thermo-magnetic properties of two ferromagnetic family compounds, MnBi and (Fe1-xCox)2B with different approaches.

Firstly, it is shown that MnBi has ability to retain its magnetization at elevated temperatures while related compositions, MnSb, suffer large diminishment. We performed DFT calculations on the thermos-magnetic properties of MnBi and MnSb. Finite temperature effects were examined by cold smearing methods to investigate the origin of this temperature dependence. The results have shown agreement with experiments, and clearly show a structural role in the thermomagnetic behavior, with marked temperature sensitivity for MnSb in its room temperature, while MnBi show little temperature dependence. Using non-linear thermal expansion effects derived from experimental measurement, total magnetization of MnBi shows a small increase with larger cell volumes. Secondly, another candidate material, (Fe1-xCox)2B, has high Tc and high MAE with no first phase transition before reaching Tc. We perform ab-initio DFT calculation of Tc as a function of Co-concentration. It is shown that the Tc is in agreement with experimental finding using periodic supercell of various size. This project is currently in progress as the Critical Material Project.