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The specific features of phononic and magnetic subsystems of type-VII clathrate EuNi2P4.
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2020-07-16 , DOI: 10.1039/d0cp02221g
V V Novikov 1 , S L Bud'ko 2 , A V Matovnikov 1 , N V Mitroshenkov 1 , K S Pilipenko 1 , N A Konoplin 3 , I V Plokhikh 4 , A Pfitzner 4 , A V Shevelkov 5
Affiliation  

A type-VII clathrate with a Eu2+ guest embedded into a Ni–P covalent framework, EuNi2P4, was synthesized by a standard two-stage ampoule synthesis and confirmed to crystallize in the orthorhombic space group Fddd with unit cell parameters a = 5.1829(1) Å, b = 9.4765(1) Å, and c = 18.9900(1) Å. A general technique for studying the lattice and magnetic properties of REE containing compounds is proposed. The temperature and field dependences of electrical resistivity ρ(T,H), magnetization M(T,H), magnetic susceptibility χ(T,H), heat capacity Cp(T), and unit cell parameters a(T), b(T), c(T), and volume V(T) were experimentally studied and analyzed at different pressures in the temperature range of 2–300 K. A cascade of anomalies in the studied dependences was identified and attributed to the magnetic phase transformation and peculiar lattice contributions at temperatures below 20 K. As a result of comparison with an isostructural clathrate SrNi2P4, the parameters of the magnetic and lattice contributions were determined. It is characteristic that the phase transition from the paramagnetic to the magnetically ordered state is not reflected in the temperature changes of the lattice parameters due to weak bonds between guest europium atoms and the Ni–P host matrix. We have constructed a tentative HT phase diagram based on the M(T) and M(H) data, which includes 6 different phases. It is established that the anomalous lattice contribution to the clathrate heat capacity CTLS(T) appears due to the effect of two-level systems (TLS) in the Eu2+ subsystem on the thermodynamic properties of EuNi2P4. The values of TLS parameters as well as the parameters of the magnetic subsystem of the clathrate were determined.

中文翻译:

VII型笼形EuNi2P4的声子和磁子系统的特定特征。

通过标准的两阶段安瓿合成法合成了具有嵌入到Ni–P共价框架EuNi 2 P 4中的Eu 2+客体的VII型笼形物,并确认其在正交晶格空间群Fddd中以晶胞参数a结晶。= 5.1829(1)Å,b = 9.4765(1)Å,c = 18.9900(1)Å。提出了研究含稀土化合物的晶格和磁性的通用技术。电阻率ρTH),磁化强度MTH),磁化率χTH),热容C pT)以及晶胞参数aT),bT),cT)和体积VT)的实验研究和分析在2–300 K的温度范围内具有不同的压力。在研究的依赖性中发现了一系列异常,并归因于20 K以下温度下的磁相变和奇特的晶格贡献。与同构笼形SrNi 2进行比较的结果P参照图4,确定了磁和晶格贡献的参数。其特征是由于客体euro原子与Ni-P主体矩阵之间的弱键,从顺磁态到磁有序态的相变不会反映在晶格参数的温度变化中。我们基于M T)和M H)数据构建了一个暂定的H T相图,其中包括6个不同的相。可以确定的是,由于the中的两能级体系(TLS)的作用,出现了对包合物热容C TLS T)的异常晶格贡献。2+子系统对EuNi 2 P 4的热力学性质的影响。确定了TLS参数的值以及包合物的磁性子系统的参数。
更新日期:2020-08-25
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