YbNi2: A heavy fermion ferromagnet

Measurements of the magnetization and specific heat of YbNi₂ binary alloy are reported. The DC magnetic susceptibility displays a ferromagnetic behavior with a Curie temperature T_C=10.5 K, one of the highest found in Yb compounds. Moreover, the temperature dependence of the specific heat exhibits a lambda anomaly with a peak of 5.12 J/mol K at 9.4 K. The analysis also shows an additional magnetic contribution around 32 K stemming from the crystalline electric field of a quartet at ${\Delta }_1=72\mathrm{K}$ and a doublet at ${\Delta }_2=126\mathrm{K}$, according to the splitting of the Yb³⁺ ion in cubic symmetry. From the magnetic contribution to the specific heat, a relatively high Kondo temperature $T_K=27\mathrm{K}$ is estimated. Below the magnetic transition, the specific heat shows a huge value of the electronic coefficient ${\gamma }_{\mathit{LT}}=573\mathrm{mJ}/\mathrm{mol}\mathrm{K}$, which is a signature of a heavy fermion behavior. Therefore, this alloy is a fine example of enhanced ferromagnetism and heavy fermion behavior among Yb compounds.     

Memory effect in MIS structures with amorphous silicon nanoparticles embedded in ultra thin SiOx matrix

Metal/${\mathrm{SiO}}_2$/a-Si-${\mathrm{SiO}}_x$/c-Si structures containing amorphous silicon nanoparticles (a-Si NPs) embedded in ultra thin ${\mathrm{SiO}}_x$ matrix are fabricated by thermal evaporation of ${\mathrm{SiO}}_x$ and sputtering of ${\mathrm{SiO}}_2$ layers followed by thermal annealing at $700{}^{\circ }\mathrm{C}$. A memory effect, due to charging of a-Si NPs in ${\mathrm{SiO}}_x$, is observed. The processes of NP charging and discharging are accomplished by applying pulses with alternative polarities. The observed shift of the flat band voltage of the high-frequency C–V curve caused by a voltage pulse of $-15\mathrm{V}$ having duration of 1 s is more than 3 V. In addition, the structures show good retention characteristics which make them promising for application in non-volatile memory devices.     

Thermoluminescence properties of copper doped zirconium oxide for UVR dosimetry

The synthesized ${\mathrm{ZrO}}_2$:Cu particles were characterized using X-ray diffraction (XRD) to determine the nanocrystallite size and crystal structure, respectively. The ${\mathrm{ZrO}}_2$:Cu powder with a crystallite size of 30–40 nm has a monoclinic structure and exhibit a thermoluminescent (TL) glow curve with two peaks centered at 130 and $180{}^{\circ }\mathrm{C}$. The TL response of ${\mathrm{ZrO}}_2$:Cu as a function of wavelength exhibited two maxima at 260 and 290 nm. The TL response of ${\mathrm{ZrO}}_2$:Cu as a function of the UV light spectral irradiance was linear in the range from 10 to $2300\mathrm{mJ}/{\mathrm{cm}}^2$. Fading and reusability of the phosphor were also studied. The results showed that ${\mathrm{ZrO}}_2$:Cu nanopowder has potential to be used as a UV dosimeter in UV radiation monitoring.     

Fast intrinsic emission in Cs2CdI4 single crystal

The spectral-luminescent studies of the ${\mathrm{Cs}}_2{\mathrm{CdI}}_4$ single crystals are reported. The fast luminescence in the 3.6–2.0 eV energy range with decay time $\tau =4.6\mathrm{ns}$ was revealed in the crystal under high-energy excitation $(E_{\mathrm{exc}}>8\mathrm{eV})$ at 9 K. This luminescence is supposed to be caused by the hole transitions between subbands of the split valence band. The energy-band picture for ${\mathrm{Cs}}_2{\mathrm{CdI}}_4$ crystals was calculated as a proof of the luminescence model.     

Electronic structure and optical properties of ABP2O7 double phosphates

Luminescence and luminescence excitation under VUV radiation of ${\mathrm{ABP}}_2{\mathrm{O}}_7$ ($\mathrm{A}=\mathrm{Na}$, K, Cs; $\mathrm{B}=\mathrm{Al}$, In) double phosphates are studied. Two emission bands peaking near 330 and 420 nm are common for investigated ${\mathrm{ABP}}_2{\mathrm{O}}_7$ crystals. The band structure and partial densities of electronic states of perfect ${\mathrm{KAlP}}_2{\mathrm{O}}_7$, ${\mathrm{LiInP}}_2{\mathrm{O}}_7$ and ${\mathrm{NaTiP}}_2{\mathrm{O}}_7$ crystals are calculated by the full-potential linear-augmented-plane-wave (FLAPW) method. It is found that the structures of the conduction bands of ${\mathrm{ABP}}_2{\mathrm{O}}_7$ crystals, which have different B cations, are appreciably different. Experimental results are compared with results of calculations of the electronic structure. Assumptions concerning the origin of luminescence in double phosphates are made.     

Principal and secondary luminescence lifetime components in annealed natural quartz

Time-resolved luminescence spectra from quartz can be separated into components with distinct principal and secondary lifetimes depending on certain combinations of annealing and measurement temperature. The influence of annealing on properties of the lifetimes related to irradiation dose and temperature of measurement has been investigated in sedimentary quartz annealed at various temperatures up to $900{}^{\circ }\mathrm{C}$. Time-resolved luminescence for use in the analysis was pulse stimulated from samples at 470 nm between 20 and $200{}^{\circ }\mathrm{C}$. Luminescence lifetimes decrease with measurement temperature due to increasing thermal effect on the associated luminescence with an activation energy of thermal quenching equal to $0.68\pm 0.01\mathrm{eV}$ for the secondary lifetime but only qualitatively so for the principal lifetime component. Concerning the influence of annealing temperature, luminescence lifetimes measured at $20{}^{\circ }\mathrm{C}$ are constant at about $33\mathrm{\mu }\mathrm{s}$ for annealing temperatures up to $600{}^{\circ }\mathrm{C}$ but decrease to about $29\mathrm{\mu }\mathrm{s}$ when the annealing temperature is increased to $900{}^{\circ }\mathrm{C}$. In addition, it was found that lifetime components in samples annealed at $800{}^{\circ }\mathrm{C}$ are independent of radiation dose in the range 85–1340 Gy investigated. The dependence of lifetimes on both the annealing temperature and magnitude of radiation dose is described as being due to the increasing importance of a particular recombination centre in the luminescence emission process as a result of dynamic hole transfer between non-radiative and radiative luminescence centres.     

Pressure behaviour of birefringence in [(CH3)2CHNH3)]4Cd3Cl10 crystal

The studies of birefringence of [(CH₃)₂CHNH₃)]₄Cd₃Cl₁₀ single crystal were carried out in the temperature interval 240–420 K and in the hydrostatic pressure range up to 570 MPa. The shift of temperature of phase transition at T₁ to higher temperature is observed with increase of pressure with the pressure coefficient ${\mathit{dT}}_1/\mathit{dp}=0.233\mathrm{K}/\mathrm{MPa}$. The shift of phase transition at T₂ to higher temperatures with the pressure coefficient ${\mathit{dT}}_2/\mathit{dp}=0.063\mathrm{K}/\mathrm{MPa}$ is observed up to about 250 MPa. At temperature T_PCP=310 K and pressure p_PCP=310 MPa the character of continuous phase transition changes to there first order and it corresponds to the tricritical point existence. Based on the studies of the temperature and pressure dependences of birefringence of [(CH₃)₂CHNH₃)]₄Cd₃Cl₁₀ crystal, its (p,T) phase diagram was constructed and its main features were discussed.     

Neutron induced alpha radiography

A radiography technique which makes use of $\alpha$-particles as penetrating radiation has been developed. The images were registered in the solid-state nuclear track detector CR-39 and the conditions to obtain the best radiography image were 2.2 h of irradiation and 25 min of etching in a KOH (30%) aqueous solution at $70{}^{\circ }\mathrm{C}$. For such conditions the resolution in the image was $23\mathrm{\mu }\mathrm{m}$. Some radiographs are shown and demonstrate the potential of the technique to inspect samples with thickness in the $\mathrm{\mu }\mathrm{m}$ range.