Critical behavior and spin polarization of a single crystal Mn$_{5}$Ge$_{3}$.

Despite difficulties of injecting spin into semiconductor using ferromagnetic metals, spin injection into semiconductor is essential for spintronics in order to take advantage of the silicon-based electronics. The intermetallic compound Mn$_{5}$Ge$_{3}$ is a promising candidate as a spin injector for semiconductor because of its relatively high Curie temperature and good lattice match with semiconductors. Recent theoretical calculations show that Mn$_{5}$Ge$_{3}$ has a spin polarization of as much as 70{\%} in the purely diffusive region. In this work, we have determined the critical exponents of a single crystal Mn$_{5}$Ge$_{3}$ using magnetometry. The critical temperature has been determined to be T$_{C}$ = 283.68$\pm $0.02 K from spontaneous magnetization with the critical exponents of $\beta $ = 0.358$\pm $0.005 and $\gamma $ = 1.367$\pm $0.005. The spin polarization of the crystal determined using point contact Andreev reflection (PCAR) is 54$\pm $2{\%}, indicating that it is a good spin injector with a substantial spin polarization compared with ordinary ferromagnetic metals such as Fe, Co and Ni. Work supported by NSF grant No. DMR05-20491 and DMR04-03849.