The Dirac semimetal PdTe2 was recently reported to be a type-I superconductor (Tc =1.64 K, µ0Hc(0) = 13.6 mT) with unusual superconductivity of the surface sheath. We here report a high-pressure study, p ≤ 2.5 GPa, of the superconducting phase diagram extracted from acsusceptibility and transport measurements on single crystalline samples. Tc(p) shows a pronounced non-monotonous variation with a maximum Tc =1.91 K around 0.91 GPa, followed by a gradual decrease to 1.27 K at 2.5 GPa. The critical field of bulk superconductivity in the limit T → 0, Hc(0, p), follows a similar trend and consequently the Hc(T, p)-curves under pressure collapse on a single curve: Hc(T, p) = Hc(0, p)[1 − (T /Tc(p)) 2 ]. Surface superconductivity is robust under pressure as demonstrated by the large superconducting screening signal that persists for applied dc-fields Ha > Hc. Surprisingly, for p ≥ 1.41 GPa the superconducting transition temperature at the surface T S c is larger than Tc of the bulk. Therefore surface superconductivity may possibly have a non-trivial nature and is connected to the topological surface states detected by ARPES. We compare the measured pressure variation of Tc with recent results from band structure calculations and discuss the importance of a Van Hove singularity.

The Cu1−xNixFe2O4 nanoparticles (with x = 0, 0.3, 0.5, 0.7, and 1) were synthesized by using spray co-precipitation method at annealing temperature Ta = 900 °C in air for 5 h. The crystal structure, microstructure, oxidation state, and magnetic properties of the samples were characterized by using X-ray diffraction, synchrotron X-ray diffraction, scanning electron microscopy, X-ray absorption spectroscopy, and vibrating sample magnetometer. It was shown that all the samples have cubic structure. Lattice constant and grain size decrease, while the Curie temperature TC increases with increasing of Ni2+ content. A small amount of Fe2+ was found in all the samples. Cation distribution was determined by using a combination of magnetization measurements, extended X-ray absorption fine structure analysis, and Rietveld refinement from synchrotron X-ray diffraction data. It was indicated that Ni2+ ions occupy in octahedral site only, while Cu2+ ions distribute in both tetrahedral and octahedral sites. The variation of magnetic parameters is discussed based on Ni2+ concentration, grain size, the cation distribution, surface effect, and the presence of Fe2+ ion in the samples.

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The MgFe 2 O 4 nanoparticles are synthesized by combustion method and annealed at different temperatures from 500 to 1000 C. Magnetic properties, morphology, valence states of iron, crystal structure, and microstructure of the samples are investigated systematically by vibrating sample magnetometer, field emission scanning electron microscope, transmission electron microscopy, X-ray absorption spectroscopy, and synchrotron X-ray diffraction. Cation distribution is determined from synchrotron X-ray diffraction data using Rietveld refinement combined with extended X-ray absorption fine structure spectroscopy. The results indicates that all the samples are phasepure with crystallite size ranging from 11 to 41 nm. By adjusting the annealing temperature, cation distribution and particle size can be changed, and consequently leading to the change in structure and magnetic properties. The saturation magnetization of the samples are enhanced significantly compared to that of the bulk material. The variation of magnetic properties is discussed based on cation distribution, particle size, valence state, surface effect, and spin canting.

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a b s t r a c tDy and Ho iron garnets in form of nanoparticles were synthesized by citrate sol-gel method. Phase formation, lattice constant and average crystallite sizes of the samples were determined via XRD measurements. Morphology and particle size distribution were studied by TEM and chemical composition was checked by EDX. Magnetic measurements in temperature range 5e600 K and in the maximum applied field of 50 kOe were carried out by using SQUID and VSM. Their magnetic parameters, including Curie temperature, magnetization compensation temperature, spontaneous magnetization, high-field susceptibility, magnetic coercivity were discussed in the framework of three interacting magnetic sublattices, magnetocrystalline anisotropy, core-shell model and compared to those of the bulk materials. Based on these analyses further evaluation on the crystallinity and homogeneity of the samples has been made.

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