Thermal conductivity of giant magnetocaloric materials showing a first-order magnetic transition

2018 Fiscal Year Final Research Report

• Project/Area Number: 16K04932
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Applied materials
• Research Institution: Kyushu University
• Principal Investigator: Wada Hirofumi 九州大学, 理学研究院, 教授 (80191831)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: 巨大磁気熱量効果 / 熱伝導 / 磁気冷凍 / 一次相転移

Outline of Final Research Achievements

We have studied the temperature dependence of the thermal conductivity \lambda of Mn-based giant magnetocaloric materials showing the first-order magnetic transition (FOMT) near room temperature. First, we synthesized high-quality (MnFeRu)2(PSi) samples by changing the compositions and the annealing temperature.
The thermal conductivity of (MnFeRu)2(PSi) is abruptly reduced on the first cooling due to the micro-cracks generated during the FOMT. On heating, the thermal conductivity smoothly increases with increasing temperature. It was found that the \lambda- T curve is not sensitive to the thermal cycle after the first cooling. This means that fewer micro-cracks were generated at subsequent phase transitions.The \lambda - T curves have small humps near the Curie temperature. We have proposed that the coexistence of a two-phase region by alloying is responsible for the humps in the \lambda - T curve.

Free Research Field

磁性物理学

Academic Significance and Societal Importance of the Research Achievements

本研究の意義は巨大磁気熱量効果を示すMn化合物について良質な試料を作製する最適条件を得たことと，熱伝導度の値が室温で2 W/m K程度であることを明らかにしたことである．前者は材料開発に，後者は磁気冷凍システムの開発に重要な情報を与えるものである．また，学術的な意義としては，熱伝導に対する格子，磁気，電子の寄与の温度依存性を考察することにより，一次相転移を示す磁性体のキュリー温度近傍の熱伝導異常に初めて物理的な説明を与えたことである．これは一次相転移を示す磁性体一般に適用できるので，その意義は大きい．