Structural and magnetic studies of metastable Gd--Cr alloys over the entire composition range

Under equilibrium conditions, Gd and Cr are immiscible. However, by vapor quenching using sputtering techniques, metastable GdxCr1-x alloys can be prepared over the entire composition range. Since pure Gd and Cr are ferromagnetic and antiferromagnetic, respectively, such metastable alloys reveal the evolution from ferromagnetic ordering to antiferromagnetic ordering. X-ray diffraction shows that the structure for samples with x<0.20 is body-centered-cubic, the same as that of Cr, whereas for x>0.20 it is hexagonal-close-packed (hcp), as is Gd. Surprisingly, no single phase amorphous state has been found. Pure Gd is ferromagnetic with Tc near room temperature. With the addition of Cr, Tc decreases slowly to about 226 K at x=0.60, and decreases rapidly as the Gd concentration is further reduced. For samples with x<0.50, magnetization at 5 K cannot be saturated even in an external field of 50 kOe, due to competing ferromagnetic and antiferromagnetic interactions. A magnetic phase diagram has been determined