Superparamagnetism, Nonrandomness, and Irradiation Effects in Cu-Ni Alloys

Abstract

The effect of neutron irradiation on copper-nickel alloys has been investigated by means of magnetic susceptibility measurements. The susceptibilities were measured by the Gouy method between 300°K and 2.0°K for a series of alloys ranging from 17.22 to 46.5 atomic percent nickel. It is shown that without superparamagnetism an unreasonable magnetic moment per nickel atom has to be assumed. This model is confirmed by irradiation studies in which samples were exposed to neutron fluxes at the Brookhaven reactor, ranging up to 2.2X10 19 neutrons/cm 2 while at 80°C, and the magnetic susceptibilities were found to increase following the irradiation. The increase was easily observable due to its strong temperature dependence, and was greatest for the samples with the highest nickel content and for samples exposed to the highest neutron fluxes. The susceptibilities of the alloys returned to their original values following an anneal in or above the temperature range where self-diffusion becomes important, while no changes in the susceptibilities were observed following anneals at lower temperatures. It is suggested that the coppernickel system is not a perfect random solid solution but tends toward segregation, and that the neutron irradiation enhances diffusion toward a true equilibrium at room temperature. This is in agreement with several other observations.

Structural characterization of electrodeposited nanophase Ni–Cu alloys

“…25 The occurrence of concomitant clustering and ordering is indeed possible if one considers pair-wise interactions beyond the first nearest neighbors. The existence of the miscibility gap gets credence from experimental studies of Meijering et al, 26 who obtained a positive heat of formation for Cu-Ni system with a maximum of 1.68 kJ mol −1 at 50 at.% nickel, corresponding to a critical temperature of about 450 K. This conclusion is also supported by the previous studies on the Cu-Ni system by different techniques such as measurement of short-range order parameters, 27 neutron irradiation, 28 and thermodynamic calculations 29,30 all of which show the tendency of the Cu-Ni solid solution to undergo clustering. However, the previous studies have concentrated mostly on Cu-rich Cu-Ni alloys or the equiatomic alloy and on alloys prepared by melting.…”

Solid State Division Annual Progress Report for Period Ending May 31, 1963

“…6 d 1t was o serve on ca cHe, germanium, an silicon. 7 The possibility of observing and measuring anomalously transmitted x rays in copper became apparent during earlier studies 8 in which Lang9 topographs were used.…”

“…7 A similar phenomenon 8 is considered to be true in Bi 2 Se 3 • Excess selenium acts as an acceptor; 9 5 Abstract of a paper which has been submitted to the journal of Applied Physics. 6 A letter which appeared in Appl.…”

“…Our earlier calculations 7 of the ranges of atoms having energies from 1 to 100 kev, slowing down through binary elastic collisions in a random solid, have been extended by using a Thomas-Fermi potential. The screening radius of the potential of the two colliding atoms is chosen by the method suggested by Firsov.…”

Resistivity and magnetoresistance of dilute solutions of Mn in Cu-Ni alloys

“…The Mn concentrations are given in atomic ppm. Values for x were not chosen throughout the concentration range be cause for X >0.44, Cu^ ^ Ni^ alloys are ferromagnetic (29). In addition, anomalous behavior in this system has been observed for x> 0.3.…”