J. Ray

Distribution of hyperfine fields in a disordered Ni48Fe52 alloy by Mossbauer effect

Mossbauer studies on a disordered Ni48Fe52 alloy are presented in the temperature range 4.2-750K. The temperature dependence of the hyperfine field at an iron site is interpreted in terms of a distribution of exchange fields due to iron atoms being present in different near neighbour environments in the disordered alloy.

Magnetic and transport behaviour in Pr3X (X=In, Sn, Ga, Ge, Ni, Co, Ru, Ir) systems

Abstract Magnetic and transport studies on Pr 3 X (X=In, Sn, Ga, Ge, Ni, Co, Ru, Ir) systems gave evidence for complex magnetic behaviour. All the systems, except X=Sn, exhibit ferromagnetic ordering. The X=Sn system exhibits antiferromagnetic ordering. For X=Ga and Sn, metamagnetic behaviour has been observed. Crystal field effects are found to play an important role in influencing magnetic behaviour. The strength of the crystal field term has also been estimated.

Distribution of 57Fe hyperfine fields in Ni-Mn alloys-a Mossbauer effect study

Mossbauer measurements on Ni-Mn alloys with 25.5 and 33 at.% Mn have been carried out and analysed using some of the concepts used in an earlier study of Ni-Mn alloys with smaller Mn concentration by Ray et al. (1974). The spectra have been explained by a distribution of hyperfine fields arising from Fe atoms located in different nearest-neighbour environments. The value of these hyperfine fields is related to their corresponding Fe exchange fields in these environments. It is found that an Fe atom occupying Mn sites shows a stronger temperature dependence of hyperfine field than those occupying Ni sites. The nature of the Fe moments in these alloys is also discussed.

Spin fluctuations in RuFe alloys with Si impurities

Abstract Resistivity studies on spin fluctuating (Ru 1− x Si x ) 98.93Fe 1.07 alloys are presented over a wide range of temperature between 50 mK and 300 K. Analyses of the incremental resistivity arising from Fe atoms indicate that the spin fluctuation temperatures in these systems are decreased by the presence of Si impurities over the pure Ru Fe ( x =0 ) value. The same trend is also observed for the superconducting transition temperature which decreases to 53 mK for the 3.5 at.% alloy from the T c value of 263 mK for the pure Ru Fe alloy.

Magnetic ordering in PdAuMn alloys

Abstract Resistivity and longitudinal magnetoresistivity studies have been carried out on several (Pd 1- x Au x ) 99.65 Mn 0.35 alloys where Au concentration is varied as x = 0, 0.008, 0.012 and 0.031. These results indicate long range ferromagnetic ordering for Au concentration upto 1.2 at%, whereas for the higher Au concentration alloys, complex short ranged magnetic ordering is observed. From the observance of resistivity maximum for 3.1 at% Au alloy and magnetoresistivity studies, spin glass type ordering is speculated in these higher Au concentration alloys.

Is there ferromagnetic to spin-glass transition in PdAuFe alloys?

Electrical resistivity studies on several (Pd1−xAux)99.93Fe0.07 alloys between 25 mK and 1 K are reported. The experiments reveal interesting features of the impurity spin polarization with the addition of Au atoms to pure PdFe0.07 alloy. Forx<0.28 the ternary alloys exhibit a familiarT2 dependence for Δρ belowTc, indicative of complex magnetic behavior. For still higher Au concentrations, resistivity maxima occur in these alloys, reflective of short-range magnetic ordering. Arguments are presented to show that this is strongly suggestive of spin-glass-type freezing at lower temperatures, as is observed in many canonical metallic spin-glasses.

Deviations of Matthiessen's rule in some PdAu alloys

Abstract The low temperature electrical resistivity of Pd1−cAuc alloys (c = 0.1, 0.22, 0.38, 0.69, 0.82 and 1.1 at.%) have been studied in detail between 1.5 and 300 K. Deviations from Matthiessens rule (DMR) have been analysed on the basis of a two-band model, and the agreement is found to be reasonably good. The parameter λ was found to decrease monotonically with temperature, and no anomalous maximum was observed as with earlier studies of Pd Ti. The variation of β shows a weak temperature dependence. The limitations of the model are also discussed.

Spin fluctuation effects in PdAuCr alloys

Abstract The electrical resistivity of four PdAu x Cr y alloys ( x = 0.9, 1.7, 2.9 at%, and y = 6.2 at%) has been measured between 2 K and 260 K to study local spin fluctuation (LSF) effects due to Cr impurities in various PdAu matrices. While for the pure PdCr 6.2 alloy the LSF temperature is 37 K, it was found to decrease with increasing the Au content to about 19 K at 3 at% Au.