MAGNETIC PHASE-DIAGRAM FOR THE SPINEL FERRITE SERIES MGFE2-XCRXO4 ANDMG1-XZNXFE1.5CR0.5O4 AS DETERMINED BY MOSSBAUER-SPECTROSCOPY

The spinel series MgFe2-xCrxO4 (0.0 less than or equal to x less than or equal to 2.0) (MFC) and Mg1-xZnxFe1.5Cr0.5O4 (0.0 less than or equa l to x less than or equal to 1.0) (MZFC) are progressively diluted on the A-sires by non-magnetic Mg2+ and/or Zn2+ ions as x increases. The different magnetic states as a function of temperature and composition could be determined by Mossbauer spectroscopy in conjunction with hig h external magnetic fields. From the spectra it was derived that only for the spinel samples MFC with x less than or equal to 0.6 and MZFC w ith x less than or equal to 0.1 a pure ferrimagnetic behavior exists d own to 4K. In the composition range 0.8 less than or equal to x less t han or equal to 1.2 for MFC and 0.2 less than or equal to x less than or equal to 0.7 for MZFC a marked canting of the A- and B-site spins w as observed below a characteristic temperature T-f indicating a re-ent rant semi-spinglass behavior. Finally, for the samples with x > 1.2 (Z FC) and x > 0.7 (MZFC) an incomplete alignment of the spins remained u p to the paramagnetic transition temperature Tg pointing to pure semi- spin glasses. Together with the temperature dependence of the average magnetic hyperfine field the complete magnetic phase diagram could be derived.