Microwave-absorbing characteristics for the composites of TP(7)

C.-H.Pengetal./MaterialsScienceandEngineeringB117(2005)27–36

Table2

DetaildataforhysteresisloopsshowninFig.4Specimena

Dopedferrite

Ni0.45Zn0.45Co0.1Fe2O4Ni0.45Zn0.45Cu0.1Fe2O4Ni0.45Zn0.45Mg0.1Fe2O4

Undopedferrite(Ni0.5Zn0.5Fe2O4)

a

33

Hc(Oe)161.4112.3112.265.82

Ms(emu/g)49.3044.5342.8531.35

Mr(emu/g)10.047.4316.9073.216

AH(kJ/m3)191.2126.8116.457.75

As-synthesizedferritescalcinedat500 Cfor1h.

tioneffects.TheeffectofCu,Mg,andCotobeaddedinNiZnferritecanbeunderstoodfromtheirchangesinpremit-tivityandpermeabilityinadditiontotheirhysteresischar-acteristicsanditwillbediscussedbrie yinthefollowingsection.

4.Discussion

Byusingthecombustionsynthesismethodandannealingprocess,wewereabletofabricateNiZn-ferritepowderswith

particlesizerangingfrom～20nmtoasizeapproximately80nm.ThecommercialNi0.5Zn0.5Fe2O4powderwithmicro-scalesizewasalsofabricated.FromFig.4andTable3,itisfoundthatthecrystallitesizeobtainedatcalcinationstemper-atureof500 C,whichis～35–45nm,hasbetterre ectionlossandbandwidththanthoseacquiredfromgreaterparticlesize(inmicro-sizedrange)oras-synthesizedone(<25nm).Recentreport[25]claimsthatacriticalparticlesizebecomesavailableastransitedfrommono-magnetic-domaintomulti-magnetic-domaintobecloseto40nm.Inthistransitionstage,bothdomainwallmotionandspinrotationareinoperation

us-

Fig.7.PermittivityandpermeabilityspectraofNi0.5Zn0.5Fe2O4-TPUcomposites.(a)ε ,(b)ε ,(c)µ ,and(d)µ .( )As-synthesizedferritewithoutheattreatment,( )synthesizedferriteannealedat500 Cfor1h,( )synthesizedferriteannealedat900 Cfor1h,and( )commercialferrite.