Magnetic properties of Mn$_{11}$Si$_{19}$ and Mn$_{4}$Si$_{7}$ in their bulk and powdery states

The purpose of this paper is to determine by experiment whether Mn$_{11}$Si$_{19}$ and Mn$_{4}$Si$_{7}$ in their bulk and powdery states have a finite magnetic moment or not. High quality bulk samples for both were prepared using the temperature gradient solution growth method. Powery samples for both were prepared by pounding bulk crystals in a mortar. Magnetisation measurements were carried out using both SQUID system and Kerr rotation system. SQUID measurements revealed that Mn$_{11}$Si$_{19}$ has finite magnetism while Mn$_{4}$Si$_{7}$ does not in their bulk states. It was also confirmed that Mn$_{4}$Si$_{7}$ became magnetic and Mn$_{11}$Si$_{19}$ exhibited a distinctive hysteresis, in their powdery state. The enhancement of magnetism in their powery states implied that the surface of the samples was to a great extent linked to its magnetism.