微波铁氧体饱和磁化强度的测量磁场及剩磁比问题

摘要

To device designers, the saturation magnetization Ms is one of important parameters of microwave ferrite materials. However, there were some confuses on the maximum magnetic flux density Bm, the saturation flux Bs and Ms in some papers, so the purpose of this article is to discuss this problem. To interpret the difference between soft ferrite and microwave ferrite, the magnetizing curve of the garnet with narrow linewidth and coercivities of commercial microwave materials are given, which shows that the saturation magnetizing field Hs for microwave ferrites is larger in order of 2 to 3 then the measuring field Hm (=5Hc~10Hc) to the hysteresis loop measurement. By means of the fact that the ratio Bm/m0Ms (»Mm/Ms)£63%~81%for Li ferrites and the ratio Bm/m0Ms (»Mm/Ms)£81%~86%for the Mn:YIG, it is revealed that a percentage of 14% ~37% of magnetizations in domains of the materials is not orientated by the measuring field Hm and it is indicated that the measured Bm can not be expressed as Bm»Bs»m0Ms for microwave ferrites like as that in soft ferrites, and the Ms value of microwave ferrites should be determined at the measuring field H>300kA/m to get the saturation state according to the IEC60556 standard. The problem of mistaking the remanence ratio R as Br/Bs is also discussed at the last.%　　微波铁氧体的饱和磁化强度 Ms是器件设计者选择材料的重要参数之一,但是一些文章常将 Bm、Bs与Ms混为一谈,本文旨在讨论这一问题。软磁铁氧体材料因为磁晶各向异性常数K1非常低,饱和磁化场Hs低,其 Bs通常由指定测量磁场 Hm下测得的 Bm(Hm»Hs)来确定。为了说明微波铁氧体与软磁铁氧体的不同,给出了小线宽石榴石材料的磁化曲线和微波铁氧体材料的矫顽力,由此推知微波铁氧体材料的饱和磁化场Hs远高于磁滞回线的测量磁场Hm(5Hc~10Hc),相差2~3个数量级。由Li铁氧体的Bm/m0Ms (»Mm/Ms)£63%~81%和Mn：YIG的Bm/m0Ms£81%~86%,说明在Hm下材料磁畴中的磁矩中有14%~37%不在磁场方向。因此对微波铁氧体来说,不能像在软磁铁氧体中那样有Bm»Bs»m0Ms的关系。所以为保证材料被磁化饱和,Ms的测量应该按照IEC60556标准在>300kA/m磁场下进行。最后讨论了经常将剩磁比R=Br/Bm误成Br/Bs问题。