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arXiv 1105.5246cond-mat.supr-con
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块体超导Bi3Ni的物理性质和电子结构表征

Physical property and electronic structure characterization of bulk superconducting Bi3Ni

Jagdish Kumar, Anuj Kumar, Arpita Vajpayee, Bhasker Gahtori, Devina Sharma, P. K. Ahluwalia, S. Auluck, V. P. S. Awana

摘要:

本文报道了Bi_3Ni系统磁性的实验和理论研究。晶体结构为正交晶系(Pnma),晶格参数a = 8.879nm,b = 4.0998nm,c = 4.099nm。标题化合物是通过石英真空封装的5 N纯度的Ni和Bi的化学计量成分经由固态反应路线合成的。超导转变温度被发现是4.1 K证实从磁化强度和比热测量。在2K时,低临界场(Hc 1)和不可逆场(Hirr)分别为150和3000 Oe。上临界场(Hc 2)确定从现场(高达4特斯拉)交流磁化率被认为是约2特斯拉在2K。用Sommerk-Debye方程C(T)= γT + βT3+δT5拟合正常态比热,得到的参数为γ= 11.08mJ/mol-K ~ 2,β= 3.73mJ/mol-K ~ 4,δ= 0.0140mJ/mol-K ~ 6。计算得到费米能级N(EF)和德拜温度ΘD处的电子态密度(DOS)分别为4.697态/eV/公式单位和127.7K。我们还估算了电子-声子耦合常数(λ)为1.23,代入MacMillan方程,则Tc = 4.5K。基于密度泛函(DFT)的计算实验确定的晶格参数表明,在这种化合物中的镍是非磁性和铁磁相互作用似乎没有发挥作用。Stoner条件I*N(EF)= 0.136/Ni原子也表明系统不具有任何铁磁性。固定自旋矩(FSM)计算固定总磁矩上的单位细胞也表明,该系统不表现出任何特征的铁磁性。

英文摘要:

We report the experimental and theoretical study on magnetic nature of Bi3Ni system. The structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879Å b = 4.0998Å and c = 4.099Å. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5N purity stoichiometric ingredients of Ni and Bi. The superconducting transition temperature is found to be 4.1 K as confirmed from magnetization and specific heat measurements. The lower critical field (Hc1) and irreversibility field (Hirr) are around 150 and 3000Oe respectively at 2K. Upper critical field (Hc2) as determined from in field (up to 4 Tesla) ac susceptibility is found to be around 2 Tesla at 2K. The normal state specific heat is fitted using Sommerfeld-Debye equation C(T) = γT + βT3+δT5 and the parameters obtained are γ= 11.08mJ/mol-K2, β= 3.73mJ/mol-K4 and δ= 0.0140mJ/mol-K6. The calculated electronic density of states (DOS) at Fermi level N(EF) and Debye temperature ΘD are 4.697 states/eV per formula unit and 127.7K respectively. We also estimated the value of electron phonon coupling constant (λ) to be 1.23, which when substituted in MacMillan equation gives Tc = 4.5K. Density functional (DFT) based calculations for experimentally determined lattice parameters show that Ni in this compound is non-magnetic and ferromagnetic interactions seem to play no role. The Stoner condition I*N(EF) = 0.136 per Ni atom also indicates that system cannot have any ferromagnetism. The fixed spin moment (FSM) calculations by fixing total magnetic moment on the unit cell also suggested that this system does not exhibit any signatures of ferromagnetism.

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