Magnetic transitions in La1-xYxMn2Si2 - Mossbauer investigation (4.2-520 K)

A set of eight tetragonal La1-xYxMn2Si2 compounds doped with Fe-57 and cove ring the entire range 0 less than or equal to x less than or equal to 1 hav e been investigated by Mossbauer effect spectroscopy over the temperature r ange 4.2-520 K. Distinct changes in the quadrupole splitting (QS) and magne tic hyperfine field (mu(0)H(hf)) values were observed around critical conce ntrations of x(c) similar to 0.15 (4.2 K) and x(c) similar to 0.2 (room tem perature; RT) as the antiferromagnetism of the Y-rich compounds gives way t o the predominant ferromagnetism of the La-rich compounds. The temperature dependences of QS and mu(0)H(hf) for the La-rich compounds (x less than or equal to 0.25) also show distinct changes in the range similar to 285-470 K which we relate to the reported magnetic phase transitions occurring in th ese critical regions. The magnetic phase diagram which we have derived for the La1-xYxMn2Si2 series from our Mossbauer measurements is in excellent ag reement with the recent findings of neutron diffraction investigations. We show that analyses of both the Mossbauer and neutron data on LaMn2Si2 give a fully consistent account of the temperature dependent canting of the magn etic structure. Finally, consistent with earlier magnetization measurements , we suggest that a magnetically frustrated state, possibly a spin glass, m ay exist within the boundary regions of these magnetic phase transitions.