物理化学学报 >> 2010, Vol. 26 >> Issue (10): 2597-2603.doi: 10.3866/PKU.WHXB20100912

热力学、热化学和溶液化学 上一篇    下一篇

D-和L-丙氨酸的低温磁相变——磁场变化下的比热和直流磁化率

王文清, 沈新春, 龚   

  1. 1. 北京大学化学与分子工程学院应用化学系, 北京分子科学国家实验室,北京100871;
    2. 北京服装学院材料科学与工程学院,北京100029
  • 收稿日期:2010-03-19 修回日期:2010-05-21 发布日期:2010-09-27
  • 通讯作者: 王文清 E-mail:wangwqchem@pku.edu.cn
  • 基金资助:

    国家重点基础研究发展规划项目(973) (2004-973-36)和国家自然科学基金(20452002)资助

Cryogenic Magnetic Transition of D- and L-Alanine: Magnetic Field Dependence of Specific Heat and DC Magnetic Susceptibility

WANG Wen-Qing, SHEN Xin-Chun, GONG Yan   

  1. 1. Beijing National Laboratory for Molecular Sciences, Department of Applied Chemistry, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China;
    2. School of Materials Science&Engineering, Beijing Institute of Fashion Technology, Beijing 100029, P. R. China
  • Received:2010-03-19 Revised:2010-05-21 Published:2010-09-27
  • Contact: WANG Wen-Qing E-mail:wangwqchem@pku.edu.cn
  • Supported by:

    The project was supported by the National Key Basic Research Programof China (973) (2004-973-36) and National Natural Science Foundation of China (20452002).

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摘要：

为了解D-和L-丙氨酸单晶晶格在极低温下是否存在磁手性相变, 在2-20K 下改变磁场强度(0, 1, 3,5 T)测定其比热. 实验结果表明比热和温度之间的函数关系很好地符合C(T)=aT 3+b/T 2 方程, 其中aT 3 项为晶格声子的贡献, 可由公式CV=(12/5)π4R(T/θD)3 来描述(θD 为德拜温度), b/T 2 项为磁场对比热的贡献. 实验发现, 在220K 范围内D-和L-丙氨酸单晶在不同磁场强度下均存在Boson 峰(在Cp /T 3-T 曲线中表现为一个最大值). 磁的贡献导致D-和L-丙氨酸单晶的四条Cp /T 3-T 曲线在2-12K 时不重合, 且在12-20K 时消失, 此即Schottky 反常. 零磁场下,D-和L-丙氨酸的Boson 峰分别为9.44 和10.86 K; 德拜温度分别为151.5 和152.7 K. 结合磁场强度1T 下的直流磁化率测定, 发现在温度低于5K 时,D-和L-丙氨酸单晶有相反的磁化率行为, 反映了核自旋和电子自旋弱相互作用的手性表现.

 

关键词: 磁相变, D-和L-丙氨酸, 比热, 直流磁化率, Boson 峰, 德拜温度

Abstract:

To understand the intrinsic asymmetries of D- and L-alanine crystal lattices, the magnetic field dependence of zero-field and 1, 3, and 5 T on the heat capacity were measured from 2 to 20 K. The obtained heat capacity data shows linear behavior that follows: C(T)=aT3+b/T2. The first aT3 term is from the lattice phonon contribution with CV=(12/5)π4R(T/θD)3 (θD is the Debye temperature). The second b/T 2 term in the fitting formula is the magnetic contribution. In this experiment, the obtained Cp data for the D- and L-alanine single crystals show a Boson peak, which is seen as a maximum in the Cp /T 3 versus T plots in the low temperature region from 2-20 K at different fields. The four Cp /T 3 versus T curves show a split between D-andL-alanine from 2-12 K and this is due to the magnetic contribution. This is absent between 12 and 20 K, which indicates the Schottky anomaly. The temperature of the Boson peak is 9.44 K for D-alanine and 10.86 K for L-alanine, and θD is 151.5 and 152.7 K for D-alanine and L-alanine in zero-field, respectively. DC magnetic susceptibility data show the chiral behavior in nuclear spin-electron spin hyperfine interaction at very low temperature.

 

Key words: Magnetic transition, D- and L-alanine, Heat capacity, DC magnetic susceptibility, Boson peak, Debye temperature

MSC2000: 

  • O642