Magnetic Properties of Bulk Amorphous La-Fe Alloys

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We have prepared three bulk amorphous La_<100-x>Fe_x alloys (x=69.4, 76.7 and 82.5 at.% Fe) by a high rate dc-triode sputtering. All of the samples are found to be amorphous by neturon diffraction measurements. The amorphous Fe alloys with nonmagnetic Y and Lu are reported to have spin-glass characteristics, while the La-Fe alloys are found to be ferromagnetic. In the latter alloys, the magnetizations are easily saturated in low applied fields, and their values suggest that the Fe moments are completely aligned. Furthermore it has been found that the saturation magnetic moment has a maximum value 1.7μB per Fe atom at around x=75, while the Curie temperature tends to decrease gradually with increasing Fe concentration. The temperature dependence of the magnetization for these alloys follows the spin-wave relation M(T)=M_0(1-BT^<3/2>-CT^<5/2>). Using the values of B and C obtained, we have estimated the mean range of the Fe-Fe exchange interaction (<r^2>). The range of the exchange increases sharply from 〜2A^2 to 〜100A^2 with increasing Fe concentration and exceeds that of crystalline Fe.
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