Models for the magnetic ac susceptibility of granular superferromagnetic CoFe/Al2_2O3_3

The magnetization and magnetic ac susceptibility, $\chi = \chi' - i \chi''$, of superferromagnetic systems are studied by numerical simulations. The Cole-Cole plot, $\chi''$ vs. $\chi'$, is used as a tool for classifying magnetic systems by their dynamical behavior. The simulations of the magnetization hysteresis and the ac susceptibility are performed with two approaches for a driven domain wall in random media. The studies are motivated by recent experimental results on the interacting nanoparticle system Co$_{80}$Fe$_{20}$/Al$_{2}$O$_{3}$ showing superferromagnetic behavior. Its Cole-Cole plot indicates domain wall motion dynamics similarly to a disordered ferromagnet, including pinning and sliding motion. With our models we can successfully reproduce the features found in the experimental Cole-Cole plots.Comment: 8 pages, 6 figure

A Novel Dielectric Anomaly in Cuprates and Nickelates: Signature of an Electronic Glassy State

The low-frequency dielectric response of hole-doped insulators La_{2}Cu_{1-x}Li_{x}O_{4} and La_{2-x}Sr_{x}NiO_{4} shows a large dielectric constant \epsilon ^{'} at high temperature and a step-like drop by a factor of 100 at a material-dependent low temperature T_{f}. T_{f} increases with frequency and the dielectric response shows universal scaling in a Cole-Cole plot, suggesting that a charge glass state is realized both in the cuprates and in the nickelates.Comment: 5 pages, 4 figure

Absence of self-averaging in the complex admittance for transport through random media

A random walk model in a one dimensional disordered medium with an oscillatory input current is presented as a generic model of boundary perturbation methods to investigate properties of a transport process in a disordered medium. It is rigorously shown that an admittance which is equal to the Fourier-Laplace transform of the first-passage time distribution is non-self-averaging when the disorder is strong. The low frequency behavior of the disorder-averaged admittance, $-1 \sim \omega^{\mu}$ where $\mu < 1$, does not coincide with the low frequency behavior of the admittance for any sample, $\chi - 1 \sim \omega$. It implies that the Cole-Cole plot of $$ appears at a different position from the Cole-Cole plots of $\chi$ of any sample. These results are confirmed by Monte-Carlo simulations.Comment: 7 pages, 2 figures, published in Phys. Rev.

BOOK REVIEW OF THE BEST OF ME WRITTEN BY NICHOLAS SPARKS

The Best of MekaryaNicholash Sparks merupakan novel yang mengisahkantentangperjalanancintaantara Dawson Cole dan Amanda Collier yang terpaksaterhalangolehkedua orang tua Amanda yang tidakmerestuicintamerekakarenaperbedaankelassosialsehinggapadaakhirnyamerekaharusberpisah.Namun, setelahsekian lama berpisahmerekabertemukembalidengankeadaan yang telahberbeda.Tugasakhirinibertujuanuntukmengkajitentangnilai-nilai moral yang adapadatokohutama.Kelebihandari novel iniadalahnilai moral yang adapadatokohutamadankelemahanterdapatpada plot danpenggunaanbahasa yang susahdipahamidari novel The Best of Me. Dalammengkajibukuini, penulismemperoleh data denganmelakukanstudikepustakaandanmelaluireferensi yang penulisperolehmelaluisumber-sumberterkait. Dapatdisimpulkanbahwa novel The Best of Me banyakmelibatkanemosi yang menyentuhpembacadanmengajarkannilaisosialberupapengorbanan yang tulusuntuk orang lain sehinggabukuinilayakuntukdibacaolehremaja yang gemardengancerita roman

Structural, Electrical Properties and Dielectric Relaxation in Na+ Ion Conducting Solid Polymer Electrolyte

Present paper reports, the structural, microstructural, electrical, dielectric properties and ion dynamics of a sodium based solid polymer electrolyte films comprising of PEO8-NaPF6+ x wt. % SN. The structural and surface morphology properties have been investigated by XRD and FESEM. Different microscopic interaction among the polymer, salt and SN have been analyzed through FTIR. The dielectric permittivity and loss tangent enable us to estimate the dc conductivity, dielectric strength, double layer capacitance, and relaxation time. The loss tangent relaxation peak shifts towards high-frequency side which indicates the decrease of relaxation time and faster ion dynamics. Further, the relation among various relaxation times ...... has been developed systematically. The ionic conductivity has been estimated in whole frequency window including JPL and displays strong dependency on SN content. The sigma representation ........ has been introduced for exploring the ion dynamics by highlighting the dispersion region in Cole-Cole plot (........) at lower frequency window and increase in the radius of semicircle indicates a decrease of relaxation time. A well convincing/logical scheme has been proposed which justify the recorded experimental data

Investigations of the effect of nonmagnetic Ca substitution for magnetic Dy on spin-freezing in Dy2Ti2O7

Physical properties of partially Ca substituted hole-doped Dy2Ti2O7 have been investigated by ac magnetic susceptibility \chi_ac(T), dc magnetic susceptibility \chi(T), isothermal magnetization M(H) and heat capacity C_p(T) measurements on Dy1.8Ca0.2Ti2O7. The spin-ice system Dy2Ti2O7 exhibits a spin-glass type freezing behavior near 16 K. Our frequency dependent \chi_ac(T) data of Dy1.8Ca0.2Ti2O7 show that the spin-freezing behavior is significantly influenced by Ca substitution. The effect of partial nonmagnetic Ca2+ substitution for magnetic Dy3+ is similar to the previous study on nonmagnetic isovalent Y3+ substituted Dy2-xYxTi2O7 (for low levels of dilution), however the suppression of spin-freezing behavior is substantially stronger for Ca than Y. The Cole-Cole plot analysis reveals semicircular character and a single relaxation mode in Dy1.8Ca0.2Ti2O7 as for Dy2Ti2O7. No noticeable change in the insulating behavior of Dy2Ti2O7 results from the holes produced by 10% Ca2+ substitution for Dy3+ ions.Comment: 9 pages, 7 figures, 1 tabl

Existence of Nearest Neighbor and Variable Range Hopping in Pr2_2ZnMnO6_6

A joint investigation of X-ray diffraction (XRD) pattern and Raman spectrum authenticate the double phase monoclinic P21/n and cubic Fd-3m structures of polycrystalline Pr2ZnMnO6 (PZM). The existence of two different conduction mechanisms (Nearest neighbor hopping and Motts variable range hopping) is observed using a combined study of conductivity, dielectric relaxation and impedance spectra in PZM. This investigation point towards a transition from nearest neighbor hoping to Motts variable range hopping mechanism due to lowering activation energy around 580 K. The charge carriers hopping between the localized acceptor states at the grain boundaries (GBs), which dominants conduction mechanism below 580 K. The ac conductivity, dielectric relaxation, Nyquist plot, and electric modulus highlight the blended effect of grains (Gs) and GBs leads to the charge carrier dynamics in PZM. The dielectric relaxation and modulus formalism are analyzed on the basis of empirical Cole-Cole model. The conduction mechanism is found to be highly correlated with the relaxation mechanism and impedance spectroscopy.Comment: 15 page

Spin Freezing in the Spin Liquid Compound FeAl2O4

Spin freezing in the $A$-site spinel FeAl$_2$O$_4$ which is a spin liquid candidate is studied using remnant magnetization and nonlinear magnetic susceptibility and isofield cooling and heating protocols. The remnant magnetization behavior of FeAl$_2$O$_4$ differs significantly from that of a canonical spin glass which is also supported by analysis of the nonlinear magnetic susceptibility term $\chi_3 (T)$. Through the power-law analysis of $\chi_3 (T)$, a spin-freezing temperature, $T_g$ = 11.4$\pm$0.9~K and critical exponent, $\gamma$ = 1.48$\pm$0.59 are obtained. Cole-Cole analysis of magnetic susceptibility shows the presence of broad spin relaxation times in FeAl$_2$O$_4$, however, the irreversible dc susceptibility plot discourages an interpretation based on conventional spin glass features. The magnetization measured using the cooling-and-heating-in-unequal-fields protocol brings more insight to the magnetic nature of this frustrated magnet and reveals unconventional glassy behaviour. Combining our results, we arrive at the conclusion that the present sample of FeAl$_2$O$_4$ consists of a majority spin liquid phase with "glassy" regions embedded.Comment: 5 pages, 6 figs, 2-column, Accepted to Phys. Rev.