Preparation and Properties of SrFe₁₂O₁₉/ZnFe₂O₄ Core/Shell Nano-powder Microwave Absorber

Abstract

The nano-powder microwave absorber SrFe 12 O 19 /ZnFe 2 O 4 with core-shell structure were prepared by two-step citrate sol-gel, with analytically pure Fe(NO 3 ) 3 , Sr(NO 3 ) 2 and Zn(NO 3 ) 2 as the main materials. The XRD, TEM, VSM and vector network analyzer were used to analyze the chemical component, structure, morphology and magnetic property of the nano-powder. The results show that when the molar ratio of and SrFe 12 O 19 to ZnFe 2 O 4 is 1:2 and calcined temperature is 850 • C, the composite powder has obvious core-shell structure and the particles are scattered homogeneously in ellipsoidal shapes or bar shapes, the particle size of the nano-powder ranges from 35 nm to 45 nm; The saturation magnetization and remanent magnetization of the composite are larger than that of the soft phase, but smaller than that of the hard due to the exchange coupling between the hard and soft phases, the coercivity larger than that of the SrFe 12 O 19 , The maximum reflection loss reaches to −35.3 dB at 17.5 GHz when matching thickness of 2 mm, with excellent absorbing properties.

Applications of exchange coupled bi-magnetic hard/soft and soft/hard magnetic core/shell nanoparticles

“…Due to increasing need for shielding of electromagnetic wave radiation at frequencies above 1 GHz, one of the most studied high frequency property of hard-soft systems is microwave absorption (i.e., reflection loss)see Section 3.3. Studies on both hard-soft core/shell nanoparticles and nanocomposites have demonstrated that the main parameters of R L can be controlled by the hard/soft ratio [45,91,123,129,271,294,[342][343][344][345][346][347][348][349][350][351][352].…”

“…8), is consistent with the above simple theoretical arguments. In some cases, two-stage loops, typical of spring-magnets, have also been observed [93][94][95]98,114,115,131,190,242,245,261,263,264,266,268,269,271,278,279,[282][283][284][285]289,294,295] (see Fig. 9).…”

“…13). Experimentally, a number of studies concerning the control of the microwave properties in different types of hard/soft systems (i.e., thin films, nanocomposites and core/shell nanoparticles) can be found in the literature [45,91,123,124,129,270,271,294,[342][343][344][345][346][347][348][349][350][351][352][353][354][355]. Many studies show that µ' and µ'' depend on the ratio of hard/soft materials both for core/shell nanoparticles [129,342,345], nanocomposites [45,[347][348][349][350][351][352] and bilayers [354].…”

“…FeNdN [82] and FeNdB [351]. The different core/shell systems have shown advances in diverse aspects of reflection loss: increase in R L [91,124,129,270,271,294,342,[344][345][346] (see Fig. 19), higher working frequencies [124,271,294] or improved bandwidths [91,344,345].…”

“…Studies on both hard-soft core/shell nanoparticles and nanocomposites have demonstrated that the main parameters of R L can be controlled by the hard/soft ratio [45,91,123,129,271,294,[342][343][344][345][346][347][348][349][350][351][352].…”