Preparation And Microwave Absorption Properties Of NiMn-based Alloys

The ferromagnetic absorbing materials is an important microwave absorbing material.Ferromagnetic Ni-Mn-X(X=Ga,In)Heusler alloys are a novel type of multifunctional materials,and they may be attractive candidates of ferromagnetic absorbing materials for their ferromagnetic properties.However,the previous works most concentrate on the study of alloys'mechanical,thermodynamic and magnetic properties but few microwave absorbing properties has been reported.The effect of alloy component on crystal structures,microstructures,martensitic transformation behaviors and magnetic properties have been investigated by methods of differential scanning calorimetry(DSC),X-ray diffraction(XRD),scanning electron microscope(SEM)and vibrating sample magnetometer(VSM).Moreover,the relationship between the alloys' chemical component,particle morphology and size of Ni-MnX(X=Ga,In)alloys and its complex permeability ?r=?'+i?",complex permittivity ?r=?'+i?",microwave absorbing properties have been established,which are based on the electromagnetic parameters of the alloy tested with vector network analyzer(VNA).The main conclusions obtained are as follows:(1)The values of the complex permittivity(?r)and permeability(?r),as well as the reflection loss(RL),absorbing bandwidth(?f,RL?-10 dB)of the polycrystalline Ni50+xMn25xGa25(x=0,1,2,3)could be effectively tuned by the alloys'chemical component.All Ni_50+xMn_25-xGa₂₅(x=0,1,2,3)alloys show significant microwave absorption properties due to the broadly effective absorbing band width and multi-resonance behavior.Particularly,the Ni2MnGa alloy,an optimal RL_min of-49.1 dB was achieved at?13.3 GHz frequency for the coating thickness of 2.57 mm.(2)The values of the ?r and ?r as well as the RL,?f of the polycrystalline Ni_50-xMn_36+xIn₁₄(x=0,1,2)could be effectively tuned by the alloys' chemical component.The samples exhibit high dielectric and magnetic resonances(resonance and anti-resonance)at the frequency of?13.2,?12.2,?10.4 GHz for the Ni_50-xMn_36+xIn₁₄(x=0,1,2)alloys,respectively.And this complementary behavior between the enhanced dielectric and weakened magnetic attenuations has not been reported in micro irregular ferromagnetic absorbing materials.The anomalously electromagnetic resonance,associated with the permeability-to-permittivity transform of electromagnetic wave can effectively improve the microwave absorption properties of the alloys.Besides,the Ni50Mn36In14 alloy,an optimal RL_min of-51.8 dB was achieved at?9.0 GHz frequency for the coating thickness of 2.99 mm.(3)The results show that the morphology of Ni2MnGa particle gradually changes from the irregular polygon to the analogous sphere,and the average particle size of Ni2MnGa particle decreases to-6.94 ?m from-3 1.04 ?m as the milling time increases to 16 h from 0 h.It should be stressed that the ?r and ?r of the alloys show a this complementary behavior between the enhanced dielectric and weakened magnetic attenuations at the frequency of?13.1,?13.3,?11.9 GHz for milling time of 4,8,16 h,respectively.The reduction of particle size and the regularity of the morphology are conducive to reduce the distance between the neighboring Ni2MnGa particles,inducing more near-field electromagnetic interaction,which brings about the permeability-to-permittivity transform of microwave and can effectively improve the microwave absorption properties of the alloys.(4)The present results indicated that the ferromagnetic Ni-Mn-X(X=Ga,In)alloys also could be attractive candidates for broadband and high-frequency microwave absorbing materials.