Magnetic properties and ferromagnetic resonance in amorphous Gd alloys

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Abstract
An investigation is reported of the magnetic properties of various amorphous alloys of Gd and Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Pt, or Ga by means of magnetic measurements and ferromagnetic resonance. The Curie temperature and the saturation magnetization were determined for each of these alloys, and the crystallization temperature was obtained by means of a differential scanning calorimeter. The presence of hysteresis and a high remanence in the magnetic isotherms of 4.2 K indicate that the coupling between the Gd spins is predominantly ferromagnetic. For Gd70Ru30, the linewidth ΔH of the resonance line was studied as a function of temperature. A substantial increase of ΔH was observed in a broad temperature range around Tc, instead of a sharp divergence as expected in the case of crystalline materials at Tc. This is in keeping with the presence of a broad distribution of local magnetizations in these alloys. From the ferromagnetic resonance experiments it was also possible to estimate the magnetocrystalline anisotropy. The values for the uniaxial anisotropy constants Ku were found, in general, to be positive (∼106 ergs/cm3). It is argued that this anisotropy originates from an anisotropic exchange interaction between the purely S‐state spins, proceeding via the 5d electrons.