Nonlinear susceptibilities as a probe to unambiguously distinguish between canonical and cluster spin glasses

Treating the randomly Fe-substituted optimally hole-doped manganite La0.7Pb0.3(Mn1−yFey)O3 (y=0.2,0.3) as a test case, we demonstrate that a combined investigation of both odd and even harmonics of the ac magnetic response permits an unambiguous distinction between the canonical and cluster spin glasses. As expected for a spin glass (SG), the nonlinear ac magnetic susceptibilities χ3(T,ω) and χ5(T,ω) (odd armonics) diverge at the SG freezing temperature Tg=80.00(3) K [Tg=56.25(5) K] in the static limit and, like the imaginary part of the linear susceptibility, follow dynamic scaling with the critical exponents β=0.56(3) [β=0.63(3)], γ=1.80(5) [γ=2.0(1)], and zν=10.1(1) [zν=8.0(5)] in the sample with composition y=0.2 (y=0.3). The nonlinear susceptibility χNL, which has contributions from both χ3 and χ5, satisfies static scaling with the same choice of Tg, β, and γ. Irrespective of the Fe concentration, the values of the critical exponents γ, ν, and η are in much better agreement with those theoretically predicted for a three-dimensional (d=3) Heisenberg chiral SG than for a d=3 Ising SG. The true thermodynamic nature of the “zero-field” spin-glass transition is preserved even in finite magnetic fields. Unlike odd harmonics, even harmonics χ2(T,ω) and χ4(T,ω) make it evident that, apart from the macroscopic length scale of the spin-glass order in the static limit, there exists a length scale that corresponds to the short-range ferromagnetic order.This work was supported by the Department of Science and Technology, India, through Grant No. IR/S5/IU-01/2006, and by the Spanish Ministry for Education through the grant No. SAB 2010-0091. S.N.K. is thankful to the Department of Science and Technology, India, for financial support through the J. C. Bose National Fellowship. Y.B. thanks the Council for Scientific and Industrial Research, India, for the financial support through a Senior Research Fellowship. The authors thank J. M. Barandiaran and J. Gutiérrez for providing the samples

Atherogenic dyslipidemia in diabetic nephropathy: lipoprotein (a), lipid ratios and atherogenic index

Background: Atherogenic lipid profile is reported to become pronounced with onset of nephropathy. Lipid ratios also indicate atherogenic dyslipidemia. Lipoprotein (a) [(Lp(a)] considered as an independent risk factor for cardiovascular diseases (CVD), may play an important role in development and progression of nephropathy in type 2 diabetes mellitus (T2DM). The present study aimed to assess atherogenic dyslipidemia in T2DM and diabetic nephropathy patients. Methods: Total cholesterol (TC), triglycerides(Tgl), high density lipoprotein (HDL), low density lipoprotein (LDL), very low density lipoprotein (VLDL), Lp(a), lipid ratios: TC/HDL, Tgl/HDL, LDL/HDL, non-HDL cholesterol and atherogenic index (AI) was assessed in T2DM (n=35), diabetic nephropathy (n=30) and healthy individuals (n=30). Means of biochemical parameters were compared by ANOVA (analysis of variance). Pearson correlation was performed to study the association between parameters. Receiver operating characteristics (ROC) curve analysis was done to assess the predictive ability of the variables.Results: Atherogenic dyslipidemia with elevated Lp(a), TC, Tgl, VLDL, LDL, non-HDL cholesterol, lipid ratios, AI and low HDL levels were observed in both T2DM patients with and without nephropathy when compared to controls. Significantly high Tgl/HDL, TC/HDL and AI were observed in diabetic nephropathy when compared to T2DM. Conclusion: T2DM and diabetic nephropathy are associated with dyslipidemia which was more pronounced in diabetic nephropathy. Elevated Lp(a) levels may be considered as an independent CVD risk marker in T2DM and diabetic nephropathy patients along with atherogenic lipid ratio indicators

Association of triglycerides/high density lipoprotein cholesterol ratio with insulin resistance in polycystic ovary syndrome

Background: Insulin resistance (IR) is frequently observed in women with polycystic ovary syndrome (PCOS). Recent studies advocated that triglyceride to high-density lipoprotein cholesterol ratio (TG/HDL-C) can be used as a simple clinical indicator of IR. Hence, the present study was performed to investigate the use of TG/HDL-C and its association with IR in PCOS.Methods: Forty-one patients with PCOS and 40 healthy age matched women were randomly enrolled. Demographic and clinical characteristics were obtained. Insulin resistance was defined by the homeostasis model assessment for insulin resistance (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI).Results: In PCOS group, the insulin, HOMA-IR and TG/HDL-C ratio were significantly higher (p=0.001) than controls while, QUICKI was lower (p=0.001). Insulin, HOMA-IR were positively correlated with TG/HDL-C (ρ=0.303, p=0.006 and ρ=0.312, p=0.005 respectively) while, QUICKI was negatively correlated (ρ=-0.698, p=0.001). In receiver operating characteristic (ROC) analysis, area under the curve (AUC) for model based on QUICKI levels was better 0.898 (95% CI: 0.811-0.955, p=0.001) than HOMA-IR 0.636 (95% CI: 0.522-0.740, p=0.03). A cut-off value 3.23 for TG/HDL-C is proposed from the model based on QUICKI with best combination of sensitivity 83.3% and specificity 86.7%.Conclusions: Results of present study support that TG/HDL-C ratio may be a simple indicator of IR in PCOS patients which helps clinicians to identify IR in small centers, where the assays for insulin measurement are not available

Observation of isotropic-dipolar to isotropic-Heisenberg crossover in Co-and Ni-substituted manganites

High-precision ac susceptibility data have been taken on the La0.7Pb0.3Mn1?y (Co, Ni)yO3 (y = 0, 0.1, 0.2 and 0.3) manganite system over a wide range of amplitudes and frequencies of the ac driving field in a temperature range that embraces the critical region near the ferromagnetic (FM)?paramagnetic (PM) phase transition (occurring at the Curie point TC). Elaborate data analysis was performed that (i) enabled the first observation of a crossover from a three-dimensional (3D; d = 3) isotropic long-range dipolar asymptotic critical behavior to a d = 3 isotropic short-range Heisenberg critical regime as the temperature is raised from TC in the compositions y 6= 0 (no such crossover is observed in the parent compound, y = 0) and (ii) brought out clearly the importance of dipole?dipole interactions between the eg electron spins and/or between eg?t2g electron spins in establishing long-range FM order in the insulating state. The final charge and spin states of Co and Ni ions, substituting for the Mn3+ and/or Mn4+ ions, are arrived at by using a scenario of substitution that is consistent not only with the present results but also with the previously published structural, thermo-gravimetric, bulk magnetization, dc magnetic susceptibility and electrical resistivity data on the same system. The marked similarity seen between the magnetic behavior of the manganite system in question and the quenched random-exchange ferromagnets, within and outside the critical region, suggests that the percolation model forms an adequate description of the FM metal-to-PM insulator transition

Unravelling the nature of ferromagnetic-paramagnetic phase transition and its bearing on colossal magnetoresistance in nanocrystalline La

The nature of the ferromagnetic (FM)-paramagnetic (PM) phase transition at $T = T_{C}$ changes from first order to second order when the average crystallite size, d, falls below 100 nm in optimally hole-doped nanocrystalline La1−xCaxMnO3. In zero field, the systems with d < 100 behave as a three-dimensional (3D) uniaxial dipolar ferromagnet in the asymptotic critical region but in finite fields, the asymptotic critical behavior changes over to that of a 3D Ising ferromagnet. How effectively polaron correlations couple magnetic degrees of freedom to the lattice decides the order of the FM-PM transition and the magnitude of colossal magnetoresistance (CMR). d alters the electron-lattice coupling and thereby enables the tuning of CMR over an unusually wide temperature range

Mean-field treatment of nonlinear susceptibilities for a ferromagnet of arbitrary spin

The intrinsic linear and nonlinear magnetic susceptibilities, χn, for a ferromagnet of arbitrary spin, calculated using the mean-field approximation, are shown to diverge in the asymptotic critical region (ACR) with the exponent γn=nγ+(n− 1)β and n=1, 2, … . This behaviour of χn in the ACR is consistent with the scaling equation of state. With increasing spin, the divergence in χn(T), as the ferromagnetic-paramagnetic phase transition temperature, TC, is approached from below or above, progressively slows down with the result that the width of the ACR increases. For a given spin, the higher the order of nonlinear susceptibility, the narrower the ACR. These results are in qualitative agreement with the critical behaviour of χn(T) observed in an archetypal ferromagnet

Proposed mathematical model for stress- strain behaviour of geopolymer concrete

In the present study, appropriate analytic stress-strain mathematical model is developed that can capture the real (observable) stress-strain behaviour of geo polymer concrete. The geo polymer concrete mixes have shown improved stress values for the same strain levels compared to that of controlled concrete mix in M20 grade. The analytical equations for the stress-strain response of conventional and geopolymer concrete mixes have been proposed in the form of y = Ax / (1+Bx+Cx2), both for ascending and descending portions of the curves with different set of values for constants. The proposed equations have shown good correlation with experimental values. The proposed empirical equations can be used as stress block in analyzing the flexural behavior of sections of controlled and geo polymer concrete. The stress-strain curves obtained in the experiment for M20 & G20 grades of controlled and geo polymer concrete exhibit a similar trend when compared to the empirical equations of modified Saenz model. So Saenz mathematical model is successfully evaluated and validated for geopolymer concrete

A facile synthesis of Au-nanoparticles decorated PbI2 single crystalline nanosheets for optoelectronic device applications

This research communication presents a rapid and facile microwave-assisted synthesis of single crystalline nanosheets (SCNSs) of hexagonal lead iodide (PbI2) decorated with Au nanoparticles, a potential optoelectronics material. Homogeneous low dimensional AuNP decoration in PbI2 resulted in a new absorption band at similar to 604 nm and a shift in band gap from 3.23 to 3.00 eV. The significant enhancement of photoluminescent (PL) intensity observed in the AuNP-PbI2 SCNSs is attributed to the coupling of the localized surface plasmon resonanzce of AuNP leading to improved excitation and emission rates of PbI2-SCNSs in the region of the localized electromagnetic field. The Au-PbI2 SCNSs display a compelling increment in photoconductivity, and its fabricated photodetector showed a stable and switchable photo-response. Due to ease of synthesis and enhanced photoconductivity along with appealing PL features, Au-PbI2 SCNS has the potential to be used as a material of choice when fabricating an optoelectronic devices of high performance