2002 Fiscal Year Final Research Report Summary
Study of magnetocaloric effects on rare-earth and iron compounds for room temperature magnetic refrigeration
Grant-in-Aid for Scientific Research (C)
|Allocation Type||Single-year Grants |
Physical properties of metals
|Research Institution||KYOTO UNIVERSITY |
WADA Hirofumi Department of Materials Science and Engineering, Associate Professor -> 京都大学, 工学研究科, 助教授 (80191831)
|Project Period (FY)
2001 – 2002
|Keywords||magnetic refrigeration / magnetocaloric effect / first-order transition / metamagnetism / magnetic transition|
In recent years, there has been increasing interest in magnetic refrigeration as an environmentally friendly alternative to conventional vapor-cycle refrigeration. The magnetic refrigeration makes use of the cycles of magnetization and demagnetization of a magnetic material, so that the development of new materials with a giant magnetocaloric effect (MCE) is strongly desired. In the previous research project of Grant-in-aid for scientific research (09555185), we have pointed out that the first-order phase transition system would show giant MCEs. In this study, we investigated MCEs of the compounds with T_c at around room temperature. The following results were obtained.
1) We started our research from focusing our attention on the compounds with rare-earths and iron. First, We measured the magnetic entropy change, ΔS_M, caused by a magnetic field. Of R_2Fe_<17> compounds (R=Pr, Ce and Ce_<0.5>Nd_<0.5>) and Gd Laves phase compounds (Gd(Co-Ni)_2 and Gd(Al-Fe)_2). However, these compounds
show at most 6 J/K kg of ΔS_M, at the peak value, which is less than half of that of Gd.
2) Then, we searched a first-order phase transition system and found MnAs. This compound shows a first-order ferromagnetic to paramagnetic transition at 317 K. The observed ΔS_M is 32 J/K kg, which is 1.7 times as large as that of Gd_sSi_2Ge_2. These results indicate that MnAs shows giant MCEs. We also found the substitution of Sb for As can tune the Curie temperature between 220 K and 317 K without any significant reduction of MCEs. These results indicate that MnAs_<1-x>Sb_x is one of the most suitable candidates for the magnetic refrigerant material at room temperature.
3) During the present research, the Chinese group reported a large MCE of La(FeCoSi)_<13>. However, a detailed magnetic phase diagram was not investigated. We studied the magnetic properties of La(Fe_<0.88>Si_<0.12-x>Co_x)_13. The compounds form a NaZn_<13>-type structure for 0【less than or equal】x【less than or equal】0.05. The Curie temperature is increased from 195 K to 260 K with increasing x from 0 to 0.05. Metamagnetic behavior was observed above T_c in the concentration range of 0【less than or equal】x【less than or equal】0.05. These results suggest large magnetocaloric effects of the present system at around room temperature. Less
Research Products (12 results)