Magnetic properties of amorphous Fe x B 1 0 0 − x ( 72 x 8 6 ) and crystalline Fe 3 B

TLDR: The magnetic ordering temperature of amorphous pure Fe has been studied by Mossbauer spectroscopy and in some cases by magnetization measurements as mentioned in this paper, and the mean hyperfine field is found to be proportional to the average Fe moment with a ratio of about 130 kOe/${\mathrm{\ensuremath{\mu}}}

Abstract: Amorphous samples of ${\mathrm{Fe}}_{x}{\mathrm{B}}_{100\ensuremath{-}x}(72l~xl~86)$ have been studied by $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy and in some cases by magnetization measurements. The magnetic ordering temperature (${T}_{C}$) decreases sharply with increasing Fe concentration; from 760 K (${\mathrm{Fe}}_{72}$${\mathrm{B}}_{28}$) to 552 K (${\mathrm{Fe}}_{86}$${\mathrm{B}}_{14}$). The value of ${T}_{C}$ of amorphous pure Fe has been extrapolated to about 220 K. Well-defined hyperfine field distributions ${P(H)}$ have been found. The mean hyperfine field is found to be proportional to the average Fe moment with a ratio of about 130 kOe/${\mathrm{\ensuremath{\mu}}}_{\mathrm{B}}$. The shape of $P(H)$ for each alloy is practically independent of temperature. At low temperatures, the effective hyperfine field (${H}_{\mathrm{eff}}$) shows a temperature dependence of ${H}_{\mathrm{eff}}(T)={H}_{\mathrm{eff}}(0)(1\ensuremath{-}B{T}^{\frac{3}{2}}\ensuremath{\cdots})$ due to spin-wave excitations. The value of ${B}_{\frac{3}{2}}=B{({T}_{C})}^{\frac{3}{2}}$ increases with Fe concentration. As the Fe concentration is increased in these alloys, the reduced hyperfine field decreases faster with reduced temperature due to a systematic change in the distribution of exchange interactions. A correlation of ${H}_{\mathrm{eff}}(0)$ and the isomer shift exists for crystalline and amorphous Fe-B systems. Crystalline ${\mathrm{Fe}}_{3}$B(${T}_{C}\ensuremath{\sim}800$ K) has been found after crystallizing amorphous samples with $xg75$ under high heating rates. At $Tl{T}_{C}$, ${\mathrm{Fe}}_{3}$B shows at least three magnetically inequivalent sites, whereas at $Tg{T}_{C}$, electric quadrupole interactions are observed. The crystal structure of ${\mathrm{Fe}}_{3}$B is likely to be tetragonal rather than orthorhombic.