Temperature dependence of the57Fe Mossbauer effect parameters for amorphous Fe73Mo7B20

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Abstract
The magnetic properties of the amorphous ferromagnet Fe73Mo7B20 have been studied from 4.2K to room temperature using the Mossbauer effect. Fe hyperfine fields, obtained from the Mossbauer measurements, show spin-wave-type behaviour and may be described by the expression (H(0)-H(T))/H(0)=BT32/+ . . . up to temperatures of about 0.55Tc. For the low-temperature region the constant B is found to be 53*10-6 K-32/. The hyperfine field distribution, P(H), was obtained from the Fe Mossbauer spectra and showed a bimodal structure at 4.2K. This two-peaked structure changed gradually to a single broad peak with a low-field tail as the temperature increased. The relative intensity of the six Mossbauer peaks given by 3:b:1:1:b:3 yields a value of b approximately=2.2 at low temperatures. For 7>or approximately=180K b changes to approximately 4.0, indicating that the magnetisation axis is in the plane of the ribbons. The isomer shift of Fe73Mo7B20 is constant at approximately 0.18 mm s-1 relative to room-temperature alpha -Fe for T80-xMoxB20 alloys at 4.2K the authors establish a correlation between the isomer shift, delta , and the Fe hyperfine field of the form delta = alpha + beta (H-H0) with beta =6.3*10-4 mm s-1 kOe-1.