Magnetic phase diagram of the Gd-Al and Gd-Cu amorphous alloy systems

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Abstract
Amorphous films of GdxAl1−x and GdyCu1−y where x and y vary from ∼0.2 to 0.8 have been prepared by sputtering. Magnetization measurements in fields from 0.1 to 18 000 Oe over the temperature range 4.2 to 300 °K allowed us to determine the magnetic phase diagram for these systems. Spin glass and ferromagnetic states as well as intermediate regions have been identified. For all compositions the paramagnetic Curie temperature is positive having values from 18 to 150 °K. When x ?0.40, GdxAl1−x displays a susceptibility cusp and relaxation effect characteristic of a spin glass. For compositions x=0.56 and 0.81 a peak in the low field susceptibility is found which is 30 °K below the ferromagnetic Curie temperature as estimated by an Arrott plot. Since magnetic saturation at 4.2 °K is not reached for these two alloys, we assign them to an intermediate state. The GdyCu1−y system also has spin glass like behavior at y=0.21 and y=0.31 but at higher concentrations only easily saturated ferromagnetism is found. Since anisotropy energies are usually small in Gd compounds, observations of a spin glass phase must reflect the presecnce of a wide variation of exchange interactions.

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