Existence of both spin-glass and mictomagnetic behaviour in the amorphous _{Fe10Ni70P14B6} alloy

Abstract

Results of the accurate magnetization measurements performed on the amorphous Fe₁₀Ni₇₀P₁₄B₆ alloy in the temperature range 20-77 K in fields upto 1 kOe are reported. The complex magnetic behaviour exhibited by this alloy has been analyzed to show that a ferromagnetic ordering, occuring on a localized microscopic scale at a temperature T₀ very close to that given by the earlier Hall effect measurements, is accompanied by a superparamagnetic behaviour which below T₀ causes at first a spin-glass freezing of the magnetic spins when they interact with one another on a long range scale and then a mictomagnetic freezing of the giant superparamagnetic clusters at a lower temperature as a result of exchange interaction between their moments and the frozen spin-glass matrix. In addition, the present results, besides providing a clear physical insight into the widely different ordering temperatures obtained for this alloy from previous Mossbauer and resistivity measurements, on one hand and from our magnetization measurements on the other, strongly suggest a magnetic origin for the observed resistivity-minimum phenomenon. In conclusion, the present alloy represents a composition in the amorphous (Fe_xNi_1-x)₈₀P₁₄B₆ system well below the percolation limit.