[en] The crystal structure and the electric and magnetic properties of the new intermetallic compounds Y₂CoSi₂, Gd₂CoSi₂, Tb₂CoSi₂ and Dy₂CoSi₂ have been investigated. They crystallise in the monoclinic Sc₂CoSi₂ structure type (space group C2/m) showing two non-equivalent atomic positions for the rare earth atoms. While Y₂CoSi₂ is a Pauli paramagnet down to 4.2 K, Tb₂CoSi₂ and Dy₂CoSi₂ undergo a ferromagnetic transition at 185 and 126 K, respectively. A second magnetic transition can be observed from ac susceptibility measurements at 13 K for Tb₂CoSi₂ and 8.5 K for Dy₂CoSi₂ (the last one detected also from electrical resistivity data). Zero field cooled and field cooled measurements as well as non-linear ac susceptibility data suggest the hypothesis of a transition from a non-collinear ferromagnetic structure to a collinear ferromagnetic one at low temperatures. From the hysteresis cycle performed at 4.2 K, the remanence and the intrinsic coercive field for both compounds were obtained

[en] Single crystals of YMn₆Sn_5.65In_0.35, grown through a flux method, have been studied by X-ray diffraction, AC-susceptibility, high-field-magnetisation and magnetoresistivity (MR) measurements. The magnetic measurements, in particular, have been performed with the magnetic field applied along both crystallographic directions. The system undergoes a ferromagnetic transition at 303 K and, when the magnetic field is applied along the a-axis, also an antiferromagnetic to ferromagnetic transition is evident in the AC-susceptibility data. Magnetisation data obtained at different temperatures with the magnetic field applied along the a-axis display a metamagnetic field-induced transition from an antiferromagnetic state to a ferromagnetic state. When the magnetic field is applied along the c-axis, a field-induced transition is observed whose transition field is a function of temperature. The MR data in the longitudinal configuration with the magnetic field applied along the a-axis, are consistent with the magnetic behaviour observed through magnetisation measurements but, nevertheless, the absolute values of the MR are lower than those obtained in polycrystalline samples. This observation suggests a stronger contribution to the MR arising from the Mn interplane correlations along the c-axis

[en] Polycrystalline samples of HfFe₆Ge₆-type YMn₆Sn_6-xIn_x compounds (0.10≤x≤0.38) have been studied by X-ray diffraction, high field magnetisation and magnetoresistance measurements. The low In content compounds order antiferromagnetically (T_N=328, 321 and 309 K for x=0.10, 0.18 and 0.21, respectively) while YMn₆Sn_5.62In_0.38 orders ferromagnetically (T_c=329 K) and undergoes a ferro- to antiferromagnetic transition on cooling (T_t=240 K). All compounds display metamagnetic behaviour at 10 K associated with giant magnetoresistance (ΔR/R∼-30% for x=0.10). The different magnetoresistance effects measured in the x=0.18 and 0.21 compound seems to be related to different textures suggesting a more pronounced magnetoresistance along the [001] direction. Results are discussed and compared with properties of isotypic series

[en] Single crystals of TmMn₆Sn_5.85Ga_0.15 were obtained using a flux method and studied by means of X-ray diffraction and magnetisation measurements as a function of temperature (10-500 K) and magnetic fields (0-9 Tesla) applied both parallel and perpendicular to the main crystallographic directions. The compound orders ferrimagnetically below 44 K then undergoes a ferri to antiferromagnetic transition on heating followed by a new transition to paramagnetic order at 350 K. In the 50-350 K temperature range, metamagnetic behaviour may be observed

[en] The present work reports a systematic and accurate study on crystal structure and chemical homogeneity of underdoped La_2-xM_xCuO₄ (M = Ba, Sr). Samples' structural characterization performed by Rietveld refinement of XRD powder diffraction profiles provided an accurate working trendline for the dopant concentration determination. Furthermore FT-IR skeletal analysis and SIMS investigations ensured chemical homogeneity even for samples with very low dopant contents

[en] Experimental studies of the physical properties of the three equiatomic compounds GdMgX (X=Al, Ga, In) are reported. GdMgAl (MgCu₂-type structure) orders ferromagnetically below 59 K. Between 70 and 300 K it follows the Curie-Weiss law with μ_eff=8.59 μ_B and θ_P=+70 K. The magnetisation, in the ordered state, saturates almost completely at 5 K in a magnetic field of 9 Tesla (μ_sat=6.71 μ_B). From several magnetisation isotherms between 10 and 120 K, the total entropy change and the refrigerant capacity of the material at 1.5, 3 and 5 T magnetic fields is evaluated. The crystal structure of the two new phases GdMgGa and GdMgIn (hexagonal ZrNiAl-type structure) is determined by single crystal X-ray analysis and the positional and displacement parameters refinements of both compounds are reported. GdMgGa orders antiferromagnetically at 15.3 K; above 50 K the compound follows the Curie-Weiss law with θ_P=-124.5 K and μ_eff=7.52 μ_B. On the contrary, no evidence of a magnetic order is observed for the GdMgIn phase. From the Curie-Weiss law, applied in the 70-290 K range, θ_P=-130.5 K and μ_eff=7.75 μ_B are obtained. The magnetisation of the two compounds does not saturate at 5 K in an applied magnetic field of 9 T (μ_sat(GdMgGa)=0.88 μ_B, μ_sat(GdMgIn)=1.05 μ_B). (orig.)

[en] The mean survival doses of T4 bacteriophage irradiated in suspension by protons were measured at six values of incident energy. Due to the thickness of the target, the beam stopped inside the suspension, so yielding the overall mean dose, averaged from the incident energy to zero. By a suitable analysis of the overall mean doses, measured at different incident energies, the mean doses in narrow intervals of energy, which may be related to define LET values, were extracted

[en] The magnetic properties of the intermetallic phases R₃Co₈Sn₄ (R=Y, Gd) are presented. The two compounds order ferro- (Y) and ferri-magnetically (Gd) with transition temperatures of 61.5 and 102.5 K, respectively. In the paramagnetic region, the Y-compound follows the Curie-Weiss law with μ=0.98 μ_B/Co and θ_P=62.0 K while a more complex behaviour, typical of a ferrimagnetic substance, is observed for Gd₃Co₈Sn₄. The experimental data, analysed in the framework of the molecular field theory, allow to obtain the exchange parameter for the Co-Co (J_Co-Co=83k_B) and of the Gd-Co (J_Gd-Co=11k_B) interactions

[en] An overview of current research in the field of REMn₆X_6-xX'_x solid solutions (RE = rare earth metals; X = Ge, Sn; X' = Ga, In) with the HfFe₆Ge₆-type structure is presented. The substitution results in a tuning of Mn-Mn interlayer interactions and a continuous transition from antiferromagnetism to ferromagnetism with increasing value of x. The effect of thermal and hydrostatic pressure on the magnetic ordering has been studied. The compounds display giant magnetoresistance (MR) and anisotropic transport properties in relation with the magnetic ordering, consistent with expectations from preliminary electronic structure calculations. The study of those compounds containing paramagnetic rare earths allows a better understanding of the magnetocrystalline anisotropy, which is dominated by the fourth-order crystal-field parameter

[en] A simultaneous magnetic and structural transition is found for Ni_2+xMn_1-xGa at 0.18≤x≤0.2. The existence of a composition range for observing the co-occurrent transition and the composition dependence of the critical temperatures are discussed in the light of the expected difference between the Curie temperatures of the austenitic and martensitic phases. A giant magnetic entropy change is deduced for the three samples, with a maximum value of the order of |ΔS_m|=15 J/kg K for a field span of 1.8 T