LiCu2O2比熱研究與3He比熱儀的校正

Abstract

我們對一系列的LiZnxCu2-xO2單晶進行比熱量測，成份從x = 0到0.1。LiCu2O2分別有兩個相變發生在22.7 K和24.5 K。我們觀察到22 K的相變具有磁的各向異性，即磁場外加於c方向比熱會呈現鐵磁態的現象，而ab平面則會呈現反鐵磁態的現象。推測是由於當磁場外加於ab平面時，自旋會被釘住；而c方向則不會被釘住所造成的結果。我們藉由擬合160 K 到300 K計算出樣品的Debye溫度，之後及即可扣除樣品的晶格比熱去計算熵值，殘餘的熵值即是與磁性、鐵電性相關。根據我們計算出來的未摻雜與有摻雜Zn樣品間的熵值差異，相當於被取代掉的自旋1/2 Cu2+的熵值。 要在低溫量出正確的比熱數據需要進行一連串的校正工作。所以分別去校正在不同溫度、磁場下溫度計，以及建立不同磁場下的addenda table。量測不具磁性的Ag，確認了γ與Debye溫度皆與Kittel書上的一致。

The specific heat of the LiZnxCu2-xO2 was measured from x = 0 to 0.1. Two magnetic phase transitions are found at 22.7 K and 24.5 K in LiCu2O2, and the magnetic anisotropy is observed at 22 K. When the magnetic field is applied in the c axis, the specific heat represents ferromagnetism. However, the specific heat represents antiferromagnetism with applied field in the ab plane. We speculated that the pinning effect only in the ab plane results the magnetic anisotropy. The Debye temperatures have been calculated by fitting the specific heat from 160 K to 300 K. Then, we subtract the phonon contribution of LiZnxCu2-xO2 to extract the entropy probably associated with the helix magnetic and ferroelectric ordering. The entropy difference between the pure and doped Zn2+ samples is proportional to the missing Cu2+ spins. After calibrations of the thermometer in different temperatures and magnetic fields, we set up addenda tables in different magnetic fields. Then, we utilized the non-magnetic standard sample, Ag, and confirm that γ term and Debye temperature are consistent with the values in Kittel’s book.