Suppression of long-range order by random fields in TbxFe1−x alloys

Abstract

The effect of random anisotropy and exchange fields on the ‘‘phase transitions’’ in amorphous magnets has been examined in Tb2Fe98 and Tb75Fe25 using small wave-vector (Q) neutron scattering. These two alloys represent opposite extremes in relative magnitude of random anisotropy fields. The neutron results for the spin correlation lengths show that neither alloy exhibits long-range magnetic order well below its spin freezing temperature of 210 K for Tb75Fe25 and approximately 245 K for Tb2Fe98. At Tf the correlation range, ξ, in Tb75Fe25 does reach a resolution limited maximum value before falling sharply to a plateau of ≊50 Å extending to low temperatures. Tb2Fe98 shows only a rounded peak of 75 Å near the magnetization-determined Tf, and, below Tf, ξ remains near its maximum value. Both alloys show marked departures from the Lorentzian cross section below Tf, and are fitted to a Lorentzian (L) plus Lorentzian squared (L2) form appropriate for random field systems.