Study On Additive-doping Effects On Mictructure And Electromagnetic Properties Of MnZn Ferrite

Manganese-zinc （MnZn） ferrites are fine ceramic ferromagnetic materialspossessing excellent magnetic properties, such as high initial permeability, low loss,high saturation magnetization and relatively high Curie temperature. Thus, they havebeen extensively adopted in industrial applications, for example, recording heads,choke coils, communication pulse transformers, and so on. The properties of MnZnferrites are strongly influenced by the composition. In these years, in order to improvethe performance of MnZn ferrites, much more attention has been paid to the selectingof appropriate additives. So in this work, after the optimizing of sintering method andtemperature, MnZn ferrites doped with different additives, such as Y³⁺, Sb³⁺, W⁶⁺andY³⁺/Ca²⁺were studied, respectively.（1） According to the study of all the samples prepared both by “one-stepsynthesis” and conventional “two-step synthesis” methods at different temperature,the preparation process was optimized that all the samples doped with differentadditives were to be fabricated by conventional “two-step synthesis” at1300℃.（2） All the samples doped with Y³⁺ions mainly contained ferrites of a typicalspinel cubic structure. With increasing doping amount of Y³⁺ions, the lattice constantincreased. The doping of Y³⁺ions promoted the grain growth of MnZn ferrites, andcertain amount of Y³⁺ions improved the density and relative density of the samples.The Curie temperature of MnZn ferrites increased with increasing doping amount ofY³⁺ions. The saturation magnetization rose after the doping of Y³⁺ions, but dropeddown with more Y³⁺ions doped; the coercivity showed an opposite trend. Both thereal and imaginary parts of permeability of the ferrites increased with increasingdoping amount of Y³⁺ions. The introducing of Y³⁺ions is against to obtain MnZnferrites of low dielectric constant, but appropriate doping amount of Y³⁺ions canreduce the dielectric loss.（3） All the samples doped with Sb³⁺ions contained ferrites of a typical spinelcubic structure. With increasing doping amount of Sb³⁺ions, the lattice constantdecreased. The doping of Sb³⁺ions could create a liquid-phase on the grain boundary and promote the grain growth of MnZn ferrites. Saturation magnetization and initialpermeability initially rose after the doping of Sb³⁺ions, but dropped down withadditional Sb³⁺doping. The Curie temperature decreased monotonously with theincreasing doping amount of Sb³⁺ions. The coercivity showed a rise with increasingdoping content of Sb³⁺ions at first, but dropped down when Sb³⁺content was morethan1.5mol%. The dielectric constant of the MnZn ferrites presented a rise withincreasing doping content of Sb³⁺ions. A small dielectric loss can be got by dopingappropriate amount of Sb³⁺ions.（4） All the samples doped with W⁶⁺ions contained ferrites of a typical spinelcubic structure. With increasing doping amount of W⁶⁺ions, the lattice constantsdecreased. The doping of W⁶⁺ions promoted the grain growth of MnZn ferrites. TheCurie temperature decreased monotonously. The saturation magnetization andpermeability rose after the doping of W⁶⁺ions, but dropped down with more W⁶⁺ionsdoped. The dielectric constant of the MnZn ferrites presented a rise with increasingdoping content of W⁶⁺ions. Appropriate doping amount of W⁶⁺ions can reduce thedielectric loss.（5） After doping of Y³⁺ions, the microstructure was not influenced withincreasing doping amount of Ca²⁺ions. The coercivity rose after doping of Ca²⁺ions.The saturation magnetization and permeability rose after the doping of Ca²⁺ions, butdropped down with more Ca²⁺ions doped. The power loss decreased after doping ofdoping of Ca²⁺ions, but rose with more Ca²⁺ions doped, indicating that appropriatedoping amount of Y³⁺/Ca²⁺ions can reduce the power loss.