Room temperature ferromagnetic Gd$_{\mathrm{5}}$Si$_{\mathrm{4}}$ nanoparticles as T2 contrast agents for MRI.*

Room temperature ferromagnetic Gd$_{\mathrm{5}}$Si$_{\mathrm{4}}$ nanoparticles were synthesized using arc-melting and ball milling. We have demonstrated that these particles can be used as improved contrast agents for magnetic resonance imaging. The ball milled Gd$_{\mathrm{5}}$Si$_{\mathrm{4}}$ nanostructured material shows ferromagnetic to paramagnetic transition near 340 K revealing long range magnetic order of Gd$_{\mathrm{5}}$Si$_{\mathrm{4}}$ phase. The phase structure and the magnetic measurements yield orthorhombic Gd$_{\mathrm{5}}$Si$_{\mathrm{4}}$ with magnetization of 45 emu/g. Echo time was measured in a 7T MRI system showing significant reduction compared to the superparamagnetic iron oxide nanoparticles. Such results show the potential of Gd$_{\mathrm{5}}$Si$_{\mathrm{4}}$ ferromagnetic nanoparticles as T2 contrast agent for magnetic resonance imaging. However these particles did not show reduction in T1 times.