A. K. Majumdar

Superconducting fluctuation study of the 110 K phase in polycrystalline Bi1.6Pb0.4Sr2Ca2Cu3Oγ high-Tc superconductor

Abstract Characterization of the Bi 1.6 Pb 0.4 Sr 2 Ca 2 Cu 3 O γ composition of high- T c superconductor, using XRD, SEM/EDAX, EPR, χ AC and ϱ ( T ) techniques, has confirmed that the sample is of single phase. The real and imaginary parts along with their higher-order harmonics of magnetic susceptibility ( χ = χ ′+i χ ″) have been investigated. The temperature dependence of the imaginary part exhibits a peak whereas the real part undergoes a sharp diamagnetic transition and the second harmonic a cusp-like peak, all at the same T c =108 K. High-resolution electrical resistivity ϱ ( T ) data on the 110 K phase sample have been taken for investigating critically the superconducting fluctuations. Using the Aslamazov and Larkin (AL) and Lawrence and Doniach (LD) models of excess conductivity, several physical parameters of the models have been estimated. The salient features, displayed by the excess conductivity analysis, are the two-dimensional superconducting fluctuations in the mean field regime (−4.0 ϵ λ )=−(0.96±0.02) and a short coherence length ( ζ 0 ) of the order of a few A. λ varies from −0.74 to −1.22 with the variation in the choice of T c between (108±1) K. Two other critical regions, beyond the mean-field one, have been observed, giving exponents −0.70 for −5.2 ϵ ϵ ϱ ( T ) has reflected exclusively one single and sharp transition for the 110 K phase. The T c and the width ( ΔT c ), estimated from d ϱT ( T ) plots, are =108 and 3 K, respectively.

Magnetic and transport properties of Metglas Fe40Ni38Mo4B18

Systematic studies of the magnetic and the transport properties are lacking in Metglas 2826 MB (Fe40Ni38Mo4B18). Low‐field magnetic susceptibility between 300 and 1000 K gives Tc=(591±2) K in the amorphous state. A thermal cycling up to 1000 K yields two crystalline magnetic phases with Tc=(760±10) K and (545±5) K. Differential thermal analysis shows that the crystallization temperature is about 810 K. The ferromagnetic anisotropy of resistivity (FAR) is very small and positive with a typical value of 0.1%. The average slope of magnetoresistivity changes from −(1.1×10−8) G−1 to −(0.55×10−8) G−1 from 300 K to 77 K. The transverse and the longitudinal magnetoresistances could be related to the tangent of the Hall angle for a number of Metglas alloys including 2826 MB by considering the normal anisotropic magnetoresistance as well as the reduction in resistance due to the removal of domain walls in a uniaxial ferromagnet.

Relaxation of thermo-remanent magnetization in different magnetic phases of Fe-rich γ-FeNiCr alloys

Abstract The time decay of the thermo-remanent magnetization (TRM) of the Fe80−xNixCr20 (14 ≤ x ≤ 30) alloys has been measured for four different magnetic phases within the fcc γ-phase using a SQUID magnetometer. In the spin-glass phase (SG) (x = 19) very distinct ageing effects are observed where M(t) can be described as M(t) = M0(t/tw)−γexp[−(t/τ)1−n] for the entire time domain. In the re-entrant spin-glass (RSG) (x = 23 and 26), M(t) can be better represented by the stretched exponential with an addition of a constant term which can be well explained by the Gabay-Toulouse (GT) model. We have also measured the linear and non-linear ac susceptibilities for the sample x = 23 and confirmed the presence of the ferromagnetic (FM) ordering down to the lowest temperature. In the RSG (x = 23), the TRM shows a minimum near Tc and a local maximum just above Tc. In the FM phase (x = 30), the popular prediction of the power law decay of the TRM is observed. The latter is indistinguishable from the stretched exponential in the antiferromagnetic (AF) phase (x = 14).

AC susceptibility apparatus for use with a closed-cycle helium refrigerator

A low cost mutual inductance bridge is constructed using only operational amplifiers. The bridge is suitable for measurement of AC magnetic susceptibility for a wide variety of magnetic materials. The measurement is done using a closed-cycle helium refrigerator from 16 to 300 K where the minimum detectable moment is 6*10-10 A m2 (6*10-7 EMU). This value could be reduced to 1*10-10 A m2 (1*10-7 EMU) if liquid helium is used as a coolant. The frequency response of this bridge is better than any other conventional one as no inductor is used in the electronic circuitry.

Spin-dependent electrical transport in ion-beam sputter deposited Fe-Cr multilayers

The temperature dependence of the electrical resistivity and magnetoresistance of Xe-ion-beam-sputtered Fe-Cr multilayers has been investigated. The electrical resistivity between 5 and 300 K in the fully ferromagnetic state, obtained by applying a field beyond the saturation field

Magnetic properties of Co-rich amorphous alloys containing Cr/Mn

{(H}_{\mathrm{sat}})

Crystallization of glassy Fe80B20-xSix (0 ≤ x ≤ 12) alloys

necessary for the antiferromagnetic- (AF-) ferromagnetic (FM) field-induced transition, shows evidence of spin-disorder resistivity as in crystalline Fe and an s-d scattering contribution (as in

Structural and electrical resistivity studies on Bi1.6Pb0.4Sr2Ca4Cu5O y composition synthesized by different routes

3d

Electrical resistivity in polycrystalline La1.8Sr0.2CuO4 and YBa2Cu3O7−δ - temperature dependence and critical fluctuations

metals and alloys). The sublattice magnetization

Coexistence of glassy antiferromagnetism and giant magnetoresistance in Fe/Cr multilayer structures

m(T)