高錳含量Mn-Ni-Sn-X (X=C、Si、Ge及Co)鐵磁形狀記憶合金磁卡效應之研究

Magnetocaloric Effect in High Mn Content Mn-Ni-Sn-X (X=C, Si, Ge and Co) Ferromagnetic Shape Memory Alloys

袁如慧(Ju-Hui Yuan)

指導教授 ： 張文成

國立中正大學/理學院/物理學系/碩士(2014年)

摘要

Ni-Mn-X (X=In、Sn及Sb) 鐵磁形狀記憶合金在外加磁場中變溫時，發生馬氏體結構相變與磁相變耦合(即一級相變)，導致許多有趣的物理現象，如巨磁卡效應、磁致應變效應、巨磁阻效應及交換偏壓等，近年來備受矚目。一級相變材料由於在相變溫度處磁化強度隨溫度陡峭變化，按照Maxwell關係必有大的等溫磁熵變。因此，本論文研究了一級相變材料之高Mn含量Mn-Ni-Sn系列鐵磁形狀記憶合金，探討成分變化對其相變溫度和磁卡效應的影響。
首先，藉由改變Mn-Ni-Sn三元之間成分，來尋找擁有最大磁熵變∆SMmax.之最佳成份。研究顯示，當薄帶成分區間在Mn50-xNi40+xSn10 (x=0, 1, 2, 3)、Mn49Ni40.75+xSn10.25-x (x=0, 0.25, 0.5, 0.75)、Mn48+xNi41Sn11-x (x=0.75, 1, 1.25, 1.5)時有良好的巨磁卡效應。而最佳磁卡特性出現於Mn49Ni41Sn10，其逆馬氏體相變溫度TM = 239.7 K及最大磁熵變ΔSMmax.=15.8 J/kg•K。
第二部分，添加第四元素C及用Si、Ge替代Mn49Ni41Sn1０中的Sn，探討相同鹵素族元素添加對其TM及磁卡效應的影響。實驗結果發現，由於產生析出相而阻礙逆馬氏體相變，使得合金薄帶之ΔSMmax.大幅衰退。因此，再進一步研究鐵磁性過渡元素Co去置換Mn對Mn49-xCoxNi41Sn10 (x=0, 0.5, 1, 1.5, 2, 3, 4)薄帶磁卡效應之影響。實驗結果顯示隨Co添加量x≥1.5時，奧氏體相的鐵磁性獲得提升，而改善了TM溫度附近馬氏體與奧氏體之間的磁化量差(∆M)，因此可以在不同應用溫區中獲得平均磁熵變為12.5 J/kg•K的優異磁卡特性。

關鍵字

磁卡效應

並列摘要

Ni-Mn-X (X=In, Sn and Sb) ferromagnetic shape memory alloys (FSMAs) have attracted significant attention due to their interesting physical properties, such as large magnetic-field-induced strain, giant magnetocaloric effects (MCEs), large magnetoresistance (MR), and exchange bias (EB). These properties make them promising for various practical applications in the field of smart, magnetic refrigeration materials and spintronics. In this study, the effect of composition on martensitic transformation temperature (TM) and magnetocaloric property of Mn-based Mn-Ni-Sn alloy ribbons have been reported.
At first, for Mn-based Mn-Ni-Sn alloy ribbons, the large ΔSMmax values are only found in a limited composition region. In order to obtain the optimal MCE property, the composition modification of Mn-Ni-Sn ternary alloy is nessessary. The experimental results show that the composition of Mn50-xNi40+xSn10 (x=0, 1, 2, 3), Mn49Ni40.75+xSn10.25-x (x=0, 0.25, 0.5, 0.75), Mn48+xNi41Sn11-x (x=0.75, 1, 1.25, 1.5) can exhibit excellent MCE properties. The optimal MCE properties of ΔSMmax=15.8 J/kg•K and TM=239.7 K are observed in Mn49Ni41Sn10 ribbons.
Secondly, the effects of C, Si and Ge substitution for Sn on phase transformations and MCE properties of Mn49Ni41Sn10-xXx (X=C, Si, Ge；x=0-2) alloy ribbons have also been investigated. It can be found that some impurities, forming an additional phase in the ribbons, which decrease the ΔSMmax values of the ribbons due to the suppression of the martensitic transformation. Furthermore, the effect of magnetic Co substitution for Mn on phase transformations and MCE properties of Mn49-xCoxNi41Sn10 (x=0-4) ribbons is also studied. The erromagnetic behavior of austenite is improved with incresing Co content originated from the enhancement of ferromagnetic exchange interaction. As a result, the magnetization difference (∆M) from martensitic to austenite is also enhanced. An average ΔSMmax value of 12.5 J/kg•K is easily obtained in different operation temperature region.

並列關鍵字

Magnetocaloric Effect

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