Soft magnetic ferrites in now use as magnetic devices have a disadvantage that the saturation magnetization is considerably lower than that of metallic soft magnetic materials. The low saturation magnetization prevents us to give a higher degree of performance for transformers and inductors and to cause an increase in the density of magnetic recordings. The present authors found out the Mn-Zn ferrites containing Er2O3 with improved saturation magnetization and relative permeability. When Er2O3 is added at the composition range of 0.005-0.5 mol% to Mn0.54Zn0.36Fe2.10O4 single crystal, saturation magnetization (σ) and relative permeability (μ1′) are increased by the addition of Er2O3 showed maximum values of 10.56 × 10-1 Wbkg-1 and 640 at 5 MHz, respectively, at about 0.05 mol%Er2O3 systems tends to increase with increasing Fe2O3 and MnO contents, but σ1 value of the ferrite containing Er2O3 increases with further increasing MnO content than that of Fe2O3-MnO-ZnO system. The compositional dependences of μr′ value for single crystals in both Fe2O3-MnO-ZnO and Fe2O3-MnO-ZnO-0.05 mol%Er2O3 systems are nearly the same. However, the Er2O3-containing ferrites exhibit the μr′ values higher than that of the ferrites without Er2O3 in the entire composition range. The effect of the Er2O3 addition on magnetic properties is closely related to the dissolve of Er3+ ions in the Mn-Zn ferrite.
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