Effect of Crystallite Size on the Magnetic Properties of GaSb/MnSb Semiconductor/Ferromagnet Composites

We have studied the effect of crystallite size on the magnetic properties of GaSb–MnSb alloys prepared by the sealed-ampule method. Using the Debye–Scherrer method, optical microscopy, and electron microscopy, we have demonstrated that raising the cooling rate from 0.1 to 60°C/s reduces the crystallite size of MnSb in 59 mol % GaSb + 41 mol % MnSb eutectic alloy and 30 mol % GaSb + 70 mol % MnSb hypereutectic alloy by a factor of ~10. The decrease in crystallite size is larger in the case of the eutectic composition. The crystallite size of MnSb has been shown to determine the magnetic properties of the alloys. The alloys are ferromagnets and reducing their crystallite size changes the behavior of their magnetoresistance and raises their Curie temperature. The eutectic material obtained at a cooling rate of 60°C/s has a negative magnetoresistance, which attests to spin polarization in the alloy. The corresponding saturation field is 0.13 T. The electrical resistance of the alloys is a linear function of temperature both in the absence of a field and in a magnetic field. The composites obtained at the higher cooling rate have a more uniform distribution of their constituent phases, which is important for application of such materials in the fabrication of spin-polarized granular structures.