Intercluster Interactions Research Articles

Investigation of Low-Temperature Magnetic Relaxation and Intercluster Interaction in Electron-Doped Ca0.85La0.15MnO3 Manganite

The low-temperature (< 100 K) phase-separated (PS) state of the electron-doped polycrystalline Ca0.85La0.15MnO3 manganite has been investigated using magnetic relaxation measurements. Analysis of the zero field-cooled (ZFC) as well as field-cooled (FC) thermoremanent magnetization (TRM) data confirms glassy behaviour of this sample at low temperatures, and the glassy feature could be attributed to the presence of weakly interacting ferromagnetic clusters within the charge-ordered antiferromagnetic matrix. This phenomenon was verified from the critical analysis of field-cooled relaxation data.

Abstract 1507: Investigation of estrogen receptor-modulated association between immune activities and patient survival in breast cancer

Abstract In breast cancer, estrogen receptor (ER) is a crucial biomarker for subtyping and predicting patients’ prognosis. Nonetheless, its modulation of immune-related genes and survival was rarely discussed. Addressing this, in the present study we devised a comprehensive analysis to compare the survival associations of immune genes between ER+ and ER- breast tumors. Specifically, we modeled immune activities by a gene set enrichment analysis of 31 immunologic gene sets defined by a recent study. Whole-genome expression profiles and ER status of 279 breast cancer patients (245 ER+ and 34 ER-) were downloaded from the Gene Expression Omnibus (GSE4922); another dataset was incorporated for validation (GSE2034). Nine immunologic gene sets were significantly predictive of relapse-free survival (RFS) in a ER+ specific manner (Cox P-values&amp;lt;0.05 in ER+ and &amp;gt;0.05 in ER-). In order to investigate the modulation of ER in gene set interactions, we calculated the Pearson correlation coefficients between gene sets in ER+ and ER- cohorts, respectively. The gene sets formed two coexpression clusters in ER+ patients (all correlation coefficients&amp;gt;0.7); one cluster was composed of protective gene sets (with hazard ratios &amp;lt;1) of dendritic cells, T cell regulatory, eosinophil, and mast cell, and the other included risk gene sets of CD4, CD8, and effector memory CD4. Interestingly, no significant intra-cluster correlation appeared in the ER- condition. We also identified inter-cluster inverse correlation between mast cell and CD8 or effector memory CD4 in ER+ patients (correlation coefficients&amp;lt;-0.6). We reason that one of the clusters accounts for naïve immune system and the other represents adaptive immune system, and crosstalk between the two systems is facilitated by inter-cluster interactions. Using an independent dataset of breast tumors (GSE2034), we corroborated all the identified intra- and inter-cluster correlated pairs (correlation coefficients&amp;gt;0.6 and &amp;lt;-0.45 for intra- and inter-cluster pairs, respectively). To further dissect the functional relevance of these ER-modulated immune activities, we performed Gene Set Enrichment Analysis (GSEA) to identify differentially activated biological functions between patients with high and low enrichment scores of an immunologic gene set. GSEA revealed significant associations with breast cancer grades, subtypes, and metastasis. In conclusion, using a gene set framework we comprehensively investigated the involvement of ER in modulating between immune activities and prognosis. Further biological investigations into our findings are warranted. Citation Format: Yi-Hsuan Chang, Yu-Chiao Chiu, Tzu-Pin Lu, Liang-Chuan Lai, Mong-Hsun Tsai, Tzu-Hung Hsiao, Eric Y Chuang. Investigation of estrogen receptor-modulated association between immune activities and patient survival in breast cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1507.

Evidence for defect-induced superconductivity up to 49 K in(Ca1−xRx)Fe2As2

To explore the origin of the unusual non-bulk superconductivity with a Tc up to 49 K reported in the rare-earth-doped CaFe2As2 , the chemical composition, magnetization, specific heat, resistivity, and annealing effect are systematically investigated on nominal (Ca1-xRx)Fe2As2 single crystals with different x's and R = La, Ce, Pr, and Nd. All display a doping-independent Tc once superconductivity is induced, a doping-dependent low field superconducting volume fraction f, and a large magnetic anisotropy {\eta} in the superconducting state, suggesting a rather inhomogeneous superconducting state in an otherwise microscale-homogenous superconductor. The wavelength dispersive spectroscopy and specific heat show the presence of defects which are closely related to f, regardless of the R involved. The magnetism further reveals that the defects are mainly superparamagnetic clusters for R = Ce, Pr, and Nd with strong intercluster interactions, implying that defects are locally self-organized. Annealing at 500 {\deg}C, without varying the doping level x, suppresses f profoundly but not the Tc. The above observations provide evidence for the crucial role of defects in the occurrence of the unusually high Tc ~ 49 K in (Ca1-xRx)Fe2As2 and are consistent with the interface-enhanced superconductivity recently proposed.

Long-range intercluster interactions of solute nanoprecipitates in Mg–Y alloys: A first-principles study

The β′ precipitate phases formed in Mg–Y alloys, which exhibit characteristic periodic arrays of Y-rich zigzag-shaped atomic clusters at regular intervals of 1.1 nm, have attracted significant attention owing to their precipitation-hardening effect on the matrix. To investigate the formation mechanism of such cluster arrays, the interaction energies between Y clusters at various distances were quantitatively evaluated using first-principles calculations based on density functional theory. We found a weak but distinct interaction between the clusters caused by the interplay between attractive chemical interactions and repulsive relaxation energies. This interplay determines the energetically favorable structure of the cluster arrangements, and these structures are consistent with the experimental observations. We suggest that the long-range intercluster interactions dominate the alignment of Y clusters, which leads to the formation of β′ precipitates in the Mg matrix, followed by the short-range clustering of Y atoms.

Influence of Cr on the nanoclusters formation and superferromagnetic behavior of Fe-Cr-Nb-B glassy alloys

High resolution imaging and electron diffraction confirm that in the as-quenched state the structure of Fe79.7−xCrxNb0.3B20 (x = 11–13 at. %) melt-spun ribbons is completely amorphous, independent of the Cr content. Energy-dispersive X-ray spectroscopy mapping emphasizes clearly the presence of Fe and Cr clusters varying from approximately 1 to 2–3 nm in size with the increase of Cr content from 11 to 13 at. %. The Fe and Cr atoms segregate the atomic scale to form nanometer sized clusters, influencing strongly the macroscopic magnetic behavior. The Curie temperature of the system, TCsystem, confirmed by the magnetic susceptibility versus temperature measurements, gives the strength of the magnetic interactions between clusters. The inter-cluster interactions are much stronger for lower contents of Cr, the microstructure is less uniform, and TCsystem increases from 290 K for 13 at. % Cr to 330 K for 11.5 at. % Cr. The whole system transforms to a ferromagnetic state through interactions between the clusters. Zero-field cooling and field cooling curves confirm the cluster behavior with a blocking temperature, Tb, of about 250 K. Above Tb, the ribbons behave as a superferromagnetic system, whilst below the blocking temperature a classical ferromagnetic behavior is observed.

MAGNETIC MEASUREMENTS OF Ni72Mn27Ti1 AND Ni72Mn25Ti3 ALLOYS

Ni1-xMnx alloys have been extensively investigated so far, mainly because of their unusual physical properties [1]. Most obvious and common behavior of Ni1-xMnx alloy is the sequence of magnetic phase transitions from paramagnetic at higher temperature, to ferromagnetic-like at intermediate temperatures and spin-glass-like properties with decreasing temperature. These behaviors are believed to originate from the competing interactions between ferromagnetic Ni–Ni, Ni–Mn and antiferromagnetic Mn–Mn pairs. Some similar work has been shown that the magnetic states and the electrical properties are significantly changed, especially at low temperatures, by the addition of a few atomic per cent of nonmagnetic Ti impurities to NiMn alloy. Magnetic measurements have been carried out for both Ni72Mn27Ti1 and Ni72Mn25Ti3 sample by using vibrating sample magnetometer (VSM). As can be seen from Fig.1, the value of magnetization sharply increases with the external magnetic field strength at low field region and, however, it can not reach a saturation state yet in the presence of a relatively strong magnetic field of even 5 kOe. The high field side of the curves are almost lineer with the external field. The measured value of saturation magnetization decreases with increasing temperature as well. The non-saturated magnetization suggests the existence of strong antiferromagnetic inter-cluster interactions mixed with ferromagnetic interactions inside the clusters [2,3,4]. By increasing the applied field, the ferromagnetic part tends to saturate, whereas the antiferromagnetic part increases linearly. Fig. 2 displays the M-T curves of the sample at the applied field of 100 Oe, respectively. It is found that for the ZFC curve start to increase at critical temperature of 90 K showing a phase transition. Then with decreasing temperature, exhibits a maximum at around 16K and start to decrease below this temperature. The decrease in magnetization below this temperature may indicate that there are strong antiferromagnetic inter-cluster interactions between the particles [2,4,5].

Weak randomness in geometrically frustrated systems: spin-glasses

We study the competition between the spin-glass (SG) phase and antiferromagnetic (AF), superantiferromagnetic or ferromagnetic (FE) order in geometrically frustrated systems. We consider a model with two types of frustration: one coming from disordered interactions (J) and another coming from the square-lattice Ising spin system with first-(J1) and second-(J2) neighbor interactions (intrinsic frustration). The disordered interactions are between clusters and they follow the van Hemmen model, which represents a limit of weak frustration. The cluster mean-field approximation is used to treat the short-range intercluster interactions. Results are exhibited in phase diagrams of the temperature T versus J for several values of . When the intrinsic frustration increases, the Néel and Curie temperatures decrease at the same time so that the SG phase appears at a lower J. Moreover, the FE correlations enhance the SG behavior, while AF correlations reduce the SG region at the same level of intrinsic frustration. These results indicate that a weak disorder in geometrically frustrated systems is able to stabilize the SG phase.

Colloidal magnetic nanocrystal clusters: variable length-scale interaction mechanisms, synergetic functionalities and technological advantages

AbstractMagnetic particles of optimized nanoscale dimensions can be utilized as building blocks to generate colloidal nanocrystal assemblies with controlled size, well-defined morphology, and tailored properties. Recent advances in the state-of-the-art surfactant-assisted approaches for the directed aggregation of inorganic nanocrystals into cluster-like entities are discussed, and the synthesis parameters that determine their geometrical arrangement are highlighted. This review pays attention to the enhanced physical properties of iron oxide nanoclusters, while it also points to their emerging collective magnetic response. The current progress in experiment and theory for evaluating the strength and the role of intra- and inter-cluster interactions is analyzed in view of the spatial arrangement of the component nanocrystals. Numerous approaches have been proposed for the critical role of dipole-dipole and exchange interactions in establishing the nature of the nanoclusters’ cooperative magnetic behavior (be it ferromagnetic or spin-glass like). Finally, we point out why the purposeful engineering of the nanoclusters’ magnetic characteristics, including their surface functionality, may facilitate their use in diverse technological sectors ranging from nanomedicine and photonics to catalysis.

Magnetic properties of Fe nano-clusters stabilized at grain boundaries of Yb films

The temperature dependence of the magnetic properties of Fe nano-sized clusters in (5.0 at. % Fe)Yb films, prepared by vapor co-deposition, has systematically been investigated using zero-field and in-field Mössbauer spectroscopy as well as AC and DC magnetization measurements. Room temperature Mössbauer spectra reveal two types of Fe clusters, with non-cubic symmetry, located at Yb grain boundaries. Spectra, taken at 4.2 K, show a complex distribution of magnetic hyperfine fields, which can be related to inhomogeneous inter-cluster interactions. In addition, zero-field and in-field Mössbauer experiments indicate that the interactions within the Fe-clusters are predominantly ferromagnetic-like and their average magnetic moments are about 80 μB. As suggested by Mössbauer and AC magnetization data, the Fe-clusters are superparamagnetic above ca. 20 K, while their magnetic behavior below this temperature is that of cluster-glass-like systems with weak inter-cluster interactions. The details of the freezing process as a function of frequency and magnetic field are discussed and magnetic anisotropy constants for these Fe clusters are estimated to be Keff ∼ 8–12 × 105 J m−3.

Design of three-shell icosahedral matryoshka clusters A@B₁₂@A2₂₀ (A = Sn, Pb; B = Mg, Zn, Cd, Mn).

We propose a series of icosahedral matryoshka clusters of A@B12@A20 (A = Sn, Pb; B = Mg, Zn, Cd), which possess large HOMO-LUMO gaps (1.29 to 1.54 eV) and low formation energies (0.06 to 0.21 eV/atom). A global minimum search using a genetic algorithm and density functional theory calculations confirms that such onion-like three-shell structures are the ground states for these A21B12 binary clusters. All of these icosahedral matryoshka clusters, including two previously found ones, i.e., [As@Ni12@As20]3− and [Sn@Cu12@Sn20]12−, follow the 108-electron rule, which originates from the high Ih symmetry and consequently the splitting of superatom orbitals of high angular momentum. More interestingly, two magnetic matryoshka clusters, i.e., Sn@Mn12@Sn20 and Pb@Mn12@Pb20, are designed, which combine a large magnetic moment of 28 µB, a moderate HOMO-LUMO gap, and weak inter-cluster interaction energy, making them ideal building blocks in novel magnetic materials and devices.

Structural aspects of heteropolyacid microemulsions.

Metrical insights from X-ray scattering studies of dense fluid phases (known as "third" phases) in the Keggin heteropolyacid-tri-n-butyl phosphate (TBP)-n-alkane system are provided. Small-angle X-ray scattering (SAXS) experiments reveal inter-acid correlation peaks corresponding to average centre-of-mass to centre-of-mass separations of 18-23 Å between P···P, Si···Si, and Al···Al of H3PW12O40, H4SiW12O40, and H5AlW12O40, respectively, consistent with the presence of TBP solvates that form by hydrogen bonding between the acids and the phosphoryl group of TBP. The Baxter sticky sphere model analyses of the SAXS data reveal identical structures for all the dense phases with inter-cluster interaction energies of ∼5kBT. We demonstrate that the sticky sphere model is an essential paradigm for interpreting SAXS and predicting mesoscale assembly in heteropolyacid microemulsions. The model parameters for the ternary polyoxometalate-amphiphile-oil systems reveal, in rigorous clarity, how the interactions between heteropolyacid solvates underpin their condensation to produce the observed scattering data. Aside from aiding researchers in predicting the physical origins of SAXS in strongly-interacting micellar systems found in natural and engineered settings, such as chemical separations, our study provides mesostructural information that complements previously observed electrochemical behaviours for third phases formed by solvent extraction involving the contact of aqueous electrolytes of dodecatungsto-phosphoric, -silicic, and -aluminic acids with organic solutions (e.g. n-dodecane and n-octane) of TBP, and by simple dissolution of the acid salts of the polyoxometalate hydrates in the same organic solutions.

Evidence for spin glass state of NdCo1−xNixO3 (x = 0.3−0.5)

Low-temperature magnetic properties of single phase NdCo1−xNixO3(x = 0.3−0.5) have been studied using ac and dc magnetic susceptibility measurements. Nickel substituted samples have been found to exhibit a different magnetic state at low temperature as compared to pristine NdCoO3. The temperature dependent dc magnetization M (T) revealed the presence of a sharp cusp occurring at characteristic temperatures TP, for x = 0.3, 0.4, 0.5. Below TP, clear effect of magnetic field can be seen in M (T) curves and TP decreases with increasing magnetic field as well as Ni substitution content. The isothermal magnetization measurements at low temperatures shows small unsaturated hysteresis loop at lowest temperature (10 K). The ac susceptibility results show a clear frequency dependent feature. These results are analyzed to distinguish superparamagnetic and spin glass behavior by using Néel-Arrhennius, Vogel-Fulcher law, and power law fitting. This analysis ruled out the superparamagnet like state and suggests the presence of significant inter-cluster interactions, giving rise to spin-glass like cooperative freezing.

Inside Back Cover: Electrical Network of Single‐Crystalline Metal Oxide Nanoclusters Wired by π‐Molecules (Angew. Chem. Int. Ed. 42/2014)

In a mixed-valence polyoxometalate electrons are usually delocalized within the cluster anion because of the low intercluster interaction. In their Communication on page 11228 ff., R. Tsunashima et al. show how mixed-valence polyoxometalate clusters can be electrically wired together by cationic π-molecules of tetrathiafulvalene derivatives. The electron-transport characteristics of the single crystal arise from electron hopping through the strong interactions between the clusters and cationic π-molecules.

Electrical network of single-crystalline metal oxide nanoclusters wired by π-molecules.

In a mixed-valence polyoxometalate, electrons are usually delocalized within the cluster anion because of low level of inter-cluster interaction. Herein, we report the structure and electrical properties of a single crystal in which mixed-valence polyoxometalates were electrically wired by cationic π-molecules of tetrathiafulvalene substituted with pyridinium. Electron-transport characteristics are suggested to represent electron hopping through strong interactions between cluster and cationic π-molecules.

Influence of packaging on the surface oxidation and magnetic properties of cobalt nanocrystals

One frequently encountered obstacle during both ambient fabrication and the use of metal nanoclusters is spontaneous oxidation, which hampers many technological applications. In this work, we studied the influence of packaging material on the surface oxidation and magnetic properties of Co nanocrystals. We demonstrate that ‘epoxy-electronic-varnish’ capping (60–80 nm) effectively preserves the magnetic properties of pristine Co nanocrystals (∼14 nm); without showing any exchange bias coupling over a period of >720 h, slower temperature variation of coercivity reminiscent of a Co single crystal and intercluster interaction dominated high blocking temperatures >300 K. Packaging by a silver (Ag) capping layer of similar thickness facilitates pronounced exchange bias compared to the even air exposed Co nanocrystals. Numerical fits M(H) = M(∞)[1 − (H*/H)1/2] to the high field part (10–50 kOe) of M–H loops yield a sharp rise in H* values at cryogenic temperatures (5–25 K) only in Ag capped Co nanocrystals, indicating a large induced anisotropy due to altered Co/Ag interfacial spin structures.

Spin-glass-like dynamics of ferromagnetic clusters in La0.75Ba0.25CoO3

We report a magnetization study of the compound La0.75Ba0.25CoO3 where the Ba2+ doping is just above the critical limit for percolation of ferromagnetic clusters. The field cooled and zero-field cooled (ZFC) magnetization exhibit thermomagnetic irreversibility and the ac susceptibility shows a frequency dependent peak at the ferromagnetic ordering temperature (TC ≈ 203 K) of the clusters. These features indicate the presence of a non-equilibrium state below TC. For the non-equilibrium state, the dynamic scaling of the imaginary part of the ac susceptibility and the static scaling of the nonlinear susceptibility clearly establish a spin-glass-like cooperative freezing of ferromagnetic clusters at 200.9(2) K. The assertion of the occurrence of spin-glass-like freezing of ferromagnetic clusters is further substantiated by ZFC ageing and memory experiments. We also observe certain dynamical features which are not present in a typical spin glass, such as: the initial magnetization after ZFC ageing first increases and then decreases with the waiting time; and there is an imperfect recovery of relaxation in negative temperature cycling experiments. This imperfect recovery transforms to perfect recovery for concurrent field cycling. Our analysis suggests that these additional dynamical features have their origin in the inter-cluster exchange interaction and cluster size distribution. The inter-cluster exchange interaction above the magnetic percolation level gives a superferromagnetic state in some granular thin films, but our results show the absence of a typical superferromagnetic-like state in La0.75Ba0.25CoO3.

Superspin glass behavior of amorphous FeO–SiO2 thin films

We have prepared amorphous xFeO∙(100 − x)SiO2 (x = 38.2, 54.8, and 67.5 in mol %) thin films by a pulsed laser deposition method and examined their magnetic properties. The temperature dependence of zero-field-cooled magnetization manifests a cusp-like peak, i.e., spin-freezing in a low temperature region. The spin-freezing temperature depends on the frequency of ac magnetic field, and the dependence is explainable in terms of the scaling law. The aging-memory effect characteristic of spin glass is also observed. Furthermore, superparamagnetic behavior is found in the variation of magnetization with magnetic field at high temperatures. These observations indicate that there exist magnetic clusters of Fe2+ ions in the amorphous FeO–SiO2 thin films and that the intercluster interactions bring about the superspin glass transition at low temperatures.

The double-Λ hypernucleus ΛΛ 11 Be

The ground-state energy of the double-Λ hypernucleus ΛΛ 11 Be is calculated within the frame-work of the five-body model ααnΛΛ. The five-body nucleus is described using the Faddeev formalism for the unequal mass clusters involved and the potential harmonics expansion of the corresponding amplitudes. The resulting coupled differential equations depend only on the inter-cluster interactions, ΛΛ, Λn, Λα, nα, and αα, which are fairly well known from previous investigations of hypernuclei. The results obtained are in excellent agreement with the recent KEK-E373 experiment as well as with the theoretical results obtained within the Gaussian expansionmethod by Hiyama et al. The ΛΛnn double hypernucleus is also discussed.

Analysis of Potential of International Inter-Cluster Cooperation in High-Tech Industries

The article deals with the background and benefits of international inter-cluster interactions. Research shows that the cluster is the most effective form of innovative development based on the concept of innovation ecosystem, and intercluster international partnership is the most appropriate form of organization for the development of high-tech-based inter-sectoral cooperation and implementation of international projects. It is shown that the consideration of high-tech industry in the framework of the structural model as mega cluster means that the synergistic advantage can be seen only with a clear organizational structure and coordinated interaction of clusters. Analysis of necessity of inter-cluster interaction is considered on example of space industry. We propose tools for serching partners and assess the effectiveness of the scheme on the basis of inter-cluster interaction network approach and the results for the regional economy.

Branching points in the low-temperature dipolar hard sphere fluid

In this contribution, we investigate the low-temperature, low-density behaviour of dipolar hard-sphere (DHS) particles, i.e., hard spheres with dipoles embedded in their centre. We aim at describing the DHS fluid in terms of a network of chains and rings (the fundamental clusters) held together by branching points (defects) of different nature. We first introduce a systematic way of classifying inter-cluster connections according to their topology, and then employ this classification to analyse the geometric and thermodynamic properties of each class of defects, as extracted from state-of-the-art equilibrium Monte Carlo simulations. By computing the average density and energetic cost of each defect class, we find that the relevant contribution to inter-cluster interactions is indeed provided by (rare) three-way junctions and by four-way junctions arising from parallel or anti-parallel locally linear aggregates. All other (numerous) defects are either intra-cluster or associated to low cluster-cluster interaction energies, suggesting that these defects do not play a significant part in the thermodynamic description of the self-assembly processes of dipolar hard spheres.