在物理學的發展中，相變一直是學界相當感興趣的一個部分，並且在日常生活中常常會出現。從平常就容易觀察到的自來水被火煮到沸騰到微觀尺度下的磁性物質的磁性相變，都能夠看到相變行為的發生。如果想要瞭解甚至應用一個未知樣品時，建構相圖是一個相當重要的步驟。而要決定一個未知物質的相圖時，必須要統合許多不同的量測結果，本論文所研究的對象是反鐵磁系統，其對應的是磁場-溫度的相圖。目前的物理性質量測系統比較容易做到的量測方式為定磁場的變溫量測，定溫的變場量測因為不固定的磁場時會造成量測環境的不穩定，所以不易進行量測；而利用本論文所提到的磁熱效應量測方式就正好需要在變動磁場下才能量測到其現象，因此就提供了一個快速、新穎且和以往不同的量測方法。磁熱效應為描述一個因為熵變而造成樣品吸放熱物理現象，而我們常會使用"熵"來描述一個物理系統的凌亂程度，根據熱力學及相變理論知道當相變發生時，熵會發生明顯的變化，因此可以利用此特性來定義一個未知樣品的相邊界進而建構出相圖。這篇碩士論文選用Nd3Co4Sn13的三元錫化物，在先前的研究之中，透過磁化率、中子散射及等溫磁化強度證明此樣品為反鐵磁樣品，而我採用磁熱效應的方式估計出熵隨磁場的變化並將其跟先前量測的結果進行比較，並發現兩個結果吻合，證明使用我所提出的磁熱效應量測方法可以有效的定義出一個未知樣品的相圖。

Abstract
In the field of physics, phase transitions are a fascinating area of study for scientists. The phenomenon of phase transition is common in our daily lives, such as the boiling of water to form gas. At a microscopic level, the transition of water from liquid to gas is akin to the magnetic transition in magnetic materials. The physical and chemical properties of a material can dramatically change around the transitions. Understanding a material’s phase diagram is crucial in realizing or applying an unknown material. However, several kinds of experiments are required to determine a material’s phase diagram. By combining the results of these experiments, scientists can obtain a phase diagram. This thesis focuses on an antiferromagnet and its field-temperature phase diagram. Practically it is easier to performtemperature-dependent measurements at fixed magnetic fields. On the contrary, field-dependent measurements at fixed temperatures are difficult, as the environment becomes unstable when sweeping the field. The measurement of magnetocaloric effects - the temperature change of a sample due to an entropy change - provides a more efficient and versatile method of determining a material’s phase diagram. By measuring a specimen’s "magnetic entropy", which describes its degree of order of magnetic moments, we can observe the sudden change in entropy that occurs at the phase transitions. This thesis focuses on the ternary intermetallic stannide Nd3Co4Sn13. Previous reports have demonstrated the specimen’s antiferromagnetic behavior via magnetic susceptibility, neutron scattering, and isothermal magnetization measurements. In this thesis, magnetocaloric effect is used to calculate entropy changes under various applied fields. By comparing these results with those obtained using other methods, we confirm the accuracy of magnetocaloric effect measurements for determining an unknown sample’s field-temperature phase diagram.

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