MÖSSBAUER Evidence for a Spin-Compensated State in Dilute Fe-Cu Alloys

Abstract

There has been considerable recent interest in the existence and nature of the bound statel 9 which is thought to be formed in certain dilute alloys between localized magnetic impurity moments and conduction-electron spins below some critical temperature characteristic of the alloy. In their recent communication, Day­ bell and SteyertlO presented evidence based on low-temperature resistivity and suscepti­ bility measurements for the formation of such a bound state consistent with some quenching of the localized moment·associated with very dilute Fe in Cu. The results of Mossbauer ex­ periments on dilute Fe in Cu in high external magnetic fields (42-136 kOe) are presented here as evidence for significant destruction of the bound state by magnetic fields for which J1H 0 ''J k TK where k T K is on the order of the energy change associated with the formation of the bound state. The fact that the Mossbau­ er hyperfine .spectrum reflects the electronic environment within atomic dimensions of the 57Fe nucleus enables us to make some conjec­ tures as to the singlet nature of the bound state. The hyperfine interaction in dilute Fe in eu al­ loys has been reported by Kitchens, Steyert, and Taylor!! using the M<1ssbauer technique in exter­ nal magnetic fields up to 62 kOe and at temper­ atures down to 0.4°K. They noted significant deviations from pure paramagnetic behavior and interpreted their results in terms of a mod­ el due to Housley and Dash,!2 who introduced a phenomenological interaction between the localized Fe spin and conduction-electron spin­ density waves. Measurements at higher fields (Ho=110 kOe) were reported by Blum, Free­ man, and Grodzins.1s In the ideal paramagnet­ ic case the hyperfine field Hhf is proportion­ al to a Brillouin function characterized by the parameters J, g, and H sat 14: