Neutron Scattering Study of Fluctuating and Static Spin Correlations in the Anisotropic Spin Glass Fe2_2TiO5_5

The anisotropic spin glass transition, in which spin freezing is observed only along the c-axis in pseudobrookite Fe$_2$TiO$_5$, has long been perplexing because the Fe$^{3+}$ moments (d$^5$) are expected to be isotropic. Recently, neutron diffraction demonstrated that surfboard-shaped antiferromagnetic nanoregions coalesce above the glass transition temperature, T$_g$ $\approx$ 55 K, and a model was proposed in which the freezing of the fluctuations of the surfboards' magnetization leads to the anisotropic spin glass state. Given this new model, we have carried out high resolution inelastic neutron scattering measurements of the spin-spin correlations to understand the temperature dependence of the intra-surfboard spin dynamics on neutron (picosecond) time-scales. Here, we report on the temperature-dependence of the spin fluctuations measured from single crystal Fe$_2$TiO$_5$. Strong quasi-elastic magnetic scattering, arising from intra-surfboard correlations, is observed well above T$_g$. The spin fluctuations possess a steep energy-wave vector relation and are indicative of strong exchange interactions, consistent with the large Curie-Weiss temperature. As the temperature approaches T$_g$ from above, a shift in spectral weight from inelastic to elastic scattering is observed. At various temperatures between 4 K and 300 K, a characteristic relaxation rate of the fluctuations is determined. Despite the freezing of the majority of the spin correlations, an inelastic contribution remains even at base temperature, signifying the presence of fluctuating intra-surfboard spin correlations to at least T/T$_g$ $\approx$ 0.1 consistent with a description of Fe$_2$TiO$_5$ as a hybrid between conventional and geometrically frustrated spin glasses.Comment: 6 figure

Ultra-structural cell distribution of the melanoma marker iodobenzamide: improved potentiality of SIMS imaging in life sciences

BACKGROUND: Analytical imaging by secondary ion mass spectrometry (SIMS) provides images representative of the distribution of a specific ion within a sample surface. For the last fifteen years, concerted collaborative research to design a new ion microprobe with high technical standards in both mass and lateral resolution as well as in sensitivity has led to the CAMECA NanoSims 50, recently introduced onto the market. This instrument has decisive capabilities, which allow biological applications of SIMS microscopy at a level previously inaccessible. Its potential is illustrated here by the demonstration of the specific affinity of a melanoma marker for melanin. This finding is of great importance for the diagnosis and/or treatment of malignant melanoma, a tumour whose worldwide incidence is continuously growing. METHODS: The characteristics of the instrument are briefly described and an example of application is given. This example deals with the intracellular localization of an iodo-benzamide used as a diagnostic tool for the scintigraphic detection of melanic cells (e.g. metastasis of malignant melanoma). B16 melanoma cells were injected intravenously to C(57)BL(6)/J(1)/co mice. Multiple B16 melanoma colonies developed in the lungs of treated animals within three weeks. Iodobenzamide was injected intravenously in tumour bearing mice six hours before sacrifice. Small pieces of lung were prepared for SIMS analysis. RESULTS: Mouse lung B16 melanoma colonies were observed with high lateral resolution. Cyanide ions gave "histological" images of the cell, representative of the distribution of C and N containing molecules (e.g. proteins, nucleic acids, melanin, etc.) while phosphorus ions are mainly produced by nucleic acids. Iodine was detected only in melanosomes, confirming the specific affinity of the drug for melanin. No drug was found in normal lung tissue. CONCLUSION: This study demonstrates the potential of SIMS microscopy, which allows the study of ultra structural distribution of a drug within a cell. On the basis of our observations, drug internalization via membrane sigma receptors can be excluded

Mini volume collapse as evidence for a three-body magnetic polaron in S m1-x e ux S

Samarium sulfide (SmS) is a nonmagnetic narrow-gap (0.06 eV) semiconductor that undergoes a transition to a metallic intermediate valence state at 6.5 kbar. Europium sulfide (EuS) is a ferromagnetic semiconductor with a Curie temperature of 16 K and a gap of 1.6 eV. Here we present a study of the lattice constant, magnetic susceptibility, and resistivity of the substitution series Sm1-xEuxS for 0 \u3c x \u3c 1. We observe a smooth interpolation of magnetic and transport behavior across the series, consistent with a virtual crystal scenario and Vegard\u27s law. Surprisingly, however, the lattice constant deviates below Vegard\u27s law in a manner that suggests parametric control of the Sm-Sm distance by the Eu moment in the manner of a magnetic polaron

Genome characteristics of facultatively symbiotic Frankia sp. strains reflect host range and host plant biogeography

Soil bacteria that also form mutualistic symbioses in plants encounter two major levels of selection. One occurs during adaptation to and survival in soil, and the other occurs in concert with host plant speciation and adaptation. Actinobacteria from the genus Frankia are facultative symbionts that form N2-fixing root nodules on diverse and globally distributed angiosperms in the “actinorhizal” symbioses. Three closely related clades of Frankia sp. strains are recognized; members of each clade infect a subset of plants from among eight angiosperm families. We sequenced the genomes from three strains; their sizes varied from 5.43 Mbp for a narrow host range strain (Frankia sp. strain HFPCcI3) to 7.50 Mbp for a medium host range strain (Frankia alni strain ACN14a) to 9.04 Mbp for a broad host range strain (Frankia sp. strain EAN1pec.) This size divergence is the largest yet reported for such closely related soil bacteria (97.8%–98.9% identity of 16S rRNA genes). The extent of gene deletion, duplication, and acquisition is in concert with the biogeographic history of the symbioses and host plant speciation. Host plant isolation favored genome contraction, whereas host plant diversification favored genome expansion. The results support the idea that major genome expansions as well as reductions can occur in facultative symbiotic soil bacteria as they respond to new environments in the context of their symbioses

Extremely Weakly Interacting ΔSz = 0 and ΔSz = 1 Excitations and Evidence for Fractional Quantization in a Magnetization Plateau: CeSb

The plateau at 1/3 of the saturation magnetization Ms in the metamagnet CeSb is accompanied by a state of ferromagnetic layers of spins in an up-up-down sequence. We measured M and the specific heat C in the plateau, spin wave analyses of which reveal two distinct branches of excitations. Those with ΔSz=1 as measured by M, coexist with a much larger population of ΔSz=0 excitations measured by C but invisible to M. The large density of ΔSz=0 excitations, their energy gap, and their seeming lack of interaction with ΔSz=1 excitations suggest an analogy with astrophysical dark matter. Additionally, in the middle of the plateau three sharp jumps in M(H) are seen, the size of which, 0.15%Ms, is consistent with fractional quantization of magnetization per site in the down-spin layers