Carbon-intercalation effects on weakly ferromagnetic ${\text{Ni}}_{3}\text{Al}$ have been studied by $^{27}\text{A}\text{l}$ spin-echo NMR techniques. The Knight shift $K$ and the nuclear spin-lattice relaxation time ${T}_{1}$ of $^{27}\text{A}\text{l}$ have been measured in the carbon-intercalated ${\text{Ni}}_{3}{\text{AlC}}_{x}$ with $x=0$, 0.01, 0.02, 0.05, and 0.1, whose Curie temperatures are 36 K, 18 K, $<2\text{ }\text{K}$, $<2\text{ }\text{K}$ and $<2\text{ }\text{K}$, respectively. The magnitude of the negative $^{27}\text{A}\text{l}$ hyperfine coupling constants were found to decrease at first, and then increase with the carbon intercalation into the body-center site of ${\text{Ni}}_{3}\text{Al}$. The linear relations between the $1/{T}_{1}T$ and the magnetic susceptibility $\ensuremath{\chi}$ indicate that the three-dimensional ferromagnetic spin fluctuations are dominant in the ${\text{Ni}}_{3}{\text{AlC}}_{x}$ system. We estimate the evolution of the characteristic temperature of spin fluctuations, ${T}_{0}$, in frequency space when the system changes from weak ferromagnetism to a nearly ferromagnetic state. Then, we analyze the temperature dependence of inverse magnetic susceptibilities and discuss the feature of the spin fluctuations in this system. As a result, the carbon-intercalation effect was found to be over a long range, inducing three-dimensional ferromagnetic quantum phase transition at $x\ensuremath{\sim}0.02$.
We report the synthesis and characterization of bulk form diluted magnetic semiconductors I-II-V Li1.1(Zn1-xCrx)As (x = 0.03, 0.05, 0.10, 0.15)with a cubic crystal structure identical to that of III-V GaAs and II-VI zinc-blende ZnSe. With p-type carriers created by excess Li, 10% Cr substitution for Zn results in a ferromagnetic ordering below TC ~ 218 K. Li(Zn,Cr)As represents another magnetic semiconducting system with the advantage of decoupling carriers and spins, where carriers are created by adding extra Li and spins are introduced by Cr substitution for Zn.
Perfluorooctanoic acid (PFOA) has been detected in various water bodies and caused harm to aquatic organisms. The aim of this study was to investigate the cytotoxicity and mechanism associated with autophagy and oxidative stress after exposure to PFOA (0, 1, 10, 100 μg/L) for 12 h on lymphocytes, which was isolated from the head kidney of Carassius auratus (C. auratus). Both of autophagy formation, cell activity, and intracellular reactive oxygen species (ROS), malondialdehyde (MDA), glutathione (GSH), and superoxide dismutase (SOD) levels were measured. The relative expression of partial autophagy-related genes autophagy related 5 (Atg 5), autophagy related 7 (Atg 7), and Beclin 1 were also cloned and detected. Homologous relationships analysis showed high identities of genes in C. auratus and other fish by blast. C. auratus lymphocytes growth inhibition rates was increased induced by PFOA. Compared with the control group, the ROS generation and the MDA content were significantly increased in all of the PFOA-treated group. Besides, decreased SOD activity and decrease of GSH activity induced by PFOA further confirmed the occurrence of oxidative stress. The number of autophagosome formations was increased in a dose-dependent manner. Compared with the control group, Atg 7 and Beclin 1 mRNA expression was elevated significantly after PFOA exposed, showing a time-dependent manner, while mRNA expression of Atg 5 was increased remarkably in 100 μg/L PFOA-treated group. Our results indicated that PFOA caused oxidative damage to lymphocytes in C. auratus and caused various autophagy signaling pathway-associated genes imbalances in the lymphocytes. Autophagy signaling pathway-associated genes imbalance could weaken antioxidant capacity and involve in the mechanism of C. auratus lymphocytes oxidative injury caused by PFOA.
We study the isovalent substitution effect by partially introducing Se on the S site in the newly discovered superconductor Nb${}_{2}$PdS${}_{5}$ (${T}_{c}\ensuremath{\sim}$ 6 K) whose upper critical field is found to be far above its Pauli paramagnetic limit. In this Nb${}_{2}$Pd(S${}_{1\ensuremath{-}x}$Se${}_{x}$)${}_{5}$ (0 $\ensuremath{\le}$ $x$ $\ensuremath{\le}$ 0.8) system, superconductivity is systematically suppressed by the Se concentration and ultimately disappears when $x\ensuremath{\ge}$ 0.5, after which a semiconductinglike ground state emerges. In spite of the considerably reduced ${T}_{c}$ with Se doping, the ratio of the upper critical field ${H}_{c2}$ to ${T}_{c}$ remains unaffected. Moreover, the size of the heat capacity jump at ${T}_{c}$ is smaller than that expected for a BCS superconductor, implying that a strong-coupling theory cannot be the origin of this large upper critical field. In addition, the low-lying quasiparticle excitations are consistent with a nodeless gap opening over the Fermi surface. These results combined impose severe constraints on any theory of exotic superconductivity in this system.
We have investigated the critical behavior near the ferromagnetic transition of TlCo2S2 single crystals and the magnetic properties of Tl(Co0.95Ni0.05)2S2 by means of magnetization measurements. The obtained critical exponents β, γ and δ of TlCo2S2 could basically satisfy the scaling equations and are found very close to the prediction of the tricritical mean-field theory. 5[Formula: see text] Ni doping drives the system to an antiferromagnetic ground state which is unstable to magnetic field, yielding metamagnetic transition. The possible existence of a tricritical point (TCP) in Tl(Co0.95Ni0.05)2S2 is also discussed.
In this article, the structure, transport and magnetic properties were studied in details for EuMn0.8Sb2 crystals with the orthorhombic structure and Mn deficiencies. It was found that the temperature dependence of the resistivity exhibits a metallic behavior in the whole measuring temperature range, different from that in the crystals without Mn deficiencies. A large positive magnetoresistance (MR) (∼127% at 2 K and ∼25% at 300 K, in 9 T field) was observed, which can be ascribed to the combination of semiclassical MR and quantum limit MR of Dirac electrons. We also observed the high mobility of the carriers and large magnetothermopower effect at low temperatures, and two magnetic transitions emerging at ∼24 K and ∼10 K, respectively, corresponding to the antiferromagnetic ordering and canted arrangement of the Eu moments. Our findings shed new light on the intrinsic properties of EuMn0.8Sb2 and demonstrate the existence of Dirac fermions.
We investigated a series of nickel-based oxyarsenides LnNiAsO (Ln=La, Ce, Pr, Nd, Sm) compounds. CeNiAsO undergoes two successive anti-ferromagnetic transitions at TN1=9.3 K and TN2=7.3 K; SmNiAsO becomes an anti-ferromagnet below TN≃3.5 K; NdNiAsO keeps paramagnetic down to 2 K but orders anti-ferromagnetically below TN≃1.3 K. Superconductivity was observed only in Kramers non-magnetic LaNiAsO and PrNiAsO with Tc=2.7 K and 0.93 K, respectively. The superconductivity of PrNiAsO is further studied by upper critical field and specific heat measurements, which reveal that PrNiAsO is a weakly coupled Kramers non-magnetic superconductor. Our work confirms that the nickel-based oxyarsenide superconductors are substantially different in mechanism to iron-based ones, and are likely to be described by the conventional superconductivity theory.
Owing to the specific topological states in nodal-line semimetals, novel topological superconductivity is expected to emerge in these systems. In this letter, by combination of the first-principles calculations and resistivity, susceptibility and specific heat measurements, we demonstrate that La$_3$Pt$_3$Bi$_4$ is a topologically nontrivial nodal-ring semimetal protected by the gliding-mirror symmetry even in the presence of spin-orbit coupling. Meanwhile, we discover bulk superconductivity with a transition temperature of $\sim$1.1 K, and an upper critical field of $\sim$0.41 T. These findings demonstrate that La$_3$Pt$_3$Bi$_4$ provides a material platform for studying novel superconductivity in the nodal-ring system.
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