Re-entrant spin-glass behaviour of geometrically frustrated SrFe3(PO4)3O

Four anomalies of magnetic origin were observed at T1 = 10.7 K, T2 11.7 K, Tf = 22.4 K, and Tc = 23.5 K in SrFe3(PO4)3O with a geometrically frustrated magnetic lattice using different techniques. SrFe3(PO4)3O shows features typical of re-entrant spin glass with the freezing temperature Tf in zero static magnetic field and the Curie temperature Tc. These features are the sharp upturn of the dc magnetization and ferromagnetic hysteresis loops on the M(H) curves below Tc, frequency-dependent rounded maxima on both the χ'(T) and χ''(T) curves at different positions, a very small anomaly of specific heat at Tf, and strong suppression of spin-glass behaviour by magnetic fields above 0.1 T. High-field magnetization measurements revealed the existence of a 1/3-magnetization plateau above 25 T at T = 1.7 K. Magnetic reflections were observed below Tc on neutron powder diffraction patterns. Additional magnetic reflections appeared below T2