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(英文)  

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

作　　者：王文清[1] 沈新春[1] 龚 

机构地区：[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

出　　处：《物理化学学报》2010年第10期2597-2603,共7页Acta Physico-Chimica Sinica

基　　金：supported by the National Key Basic Research Program of China(973)(2004-973-36);National Natural Science Foundation of China(20452002)~~

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2-20 K下改变磁场强度(0,1,3,5T)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)=aT3+b/T2方程,其中aT3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/T2项为磁场对比热的贡献.实验发现,在2-20 K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/T3-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/T3-T曲线在2-12 K时不重合,且在12-20 K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1 T下的直流磁化率测定,发现在温度低于5 K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.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/T3 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-and L-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.

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 

分 类 号：O482.5[理学—固体物理]