Abstract
Recently there have been several theoretical reports about models of amorphous transition metal alloys which take into account the fluctuations of local magnetic moments due to structural disorder.12 It is predicted that the local atomic moment on an atom depends on the number of first near neighbors with short distances (contracted atoms) and it could be positive, negative, or negligible. An amorphous Fe–Zr system could be a typical system to study these features which have a key role in determining the magnetic structure. Fe90Zr10 orders ferromagnetically at 230 K and exhibits a mixed state at T<30 K showing spin glasslike behavior. Here we present the results on Mn and Ru substitution for Fe in Fe90Zr10. Mn is known to couple antiferromagnetically (AF) to Fe while Ru is expected to be nonmagnetic. We find that Mn reduces the Curie temperature (Tc) gradually while the spin freezing temperature (Tf) remains nearly constant. However, in the case of Ru, Tf drastically increases and 5 at. % Ru drives the system to a clear spin glass state. Hyperfine field studies show gradual evolution of AF coupled spins and their distribution, pointing out the existence of a well defined bimodal distribution. Fe–Fe exchange is believed to become antiferromagnetic for Fe–Fe distances <0.15 nm and the possible occurrence of short Fe–Fe distances in an amorphous matrix is often cited as the reason for the competing interactions to occur. However, Ru with a larger atomic size should have resulted in long Fe–Fe distance (which we have found in crystalline Fe2Zr which is a closed packed structure3). We propose that the dilution of Fe moment and the band modifications due to Ru substitution seemed to promote antiferromagnetic coupling in a Fe–Zr system.
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