The earliest microwave absorbing materials (MAMs) are fabricated in the early 20th century for military purpose to inhibit radar detection. Currently, the application of MAMs has been existing in every part of human's life to prevent radiation and interference. The microwave absorbant and microwave absorbing coatings classified by composition including alloys, metal oxides, conductive polymers, carbon materials, ceramic materials both in traditional and innovative forms are introduced in this work. Considering the harsh and complex application environment, MAMs with high temperature resistance and infrared-compatible stealth performance are involved. Metamaterials, showing excellent electromagnetic properties which are far beyond that of the materials can achieve, including perfect absorber, digitally coded control metamaterials, bionic structural materials, and adjustable smart metamaterials, are also introduced specifically in this work. In addition, to investigate electromagnetic response of absorbant, the first-principles calculations works are overviewed. The electromagnetic properties, loss mechanisms, structure, fabrication method, regulation approaches, designing principles, current applications, and future prospects of MAMs are involved in this work. This work gives a comprehensively overview over the MAMs for their theoretical and experimental advances in recent years including the military radar (frequency range of 2–18 GHz) stealth materials, relevant infrared compatible (infrared-visible, infrared-radar, infrared-laser) stealth materials, and other stealth materials with multifrequency adaptability.

Research advances in composition, structure and mechanisms of microwave absorbing materials

We have investigated the effect of Cr substitution for Fe on the spin polarization, P, of Co2CrxFe1−xSi alloys using the point contact Andreev reflection method. A steep increase from P=0.57 to P=0.64 occurs by a small substitution of Cr for Fe of x=0.02, thereafter P values are constant for higher Cr concentrations up to x=0.4. The increase in spin polarization can be attributed to both the improved L21 ordering found experimentally as well as the half-metallicity predicted by ab initio calculations in the composition range of 0≤x≤0.5. We propose the composition range of 0.02≤x≤0.1 is the most promising for ferromagnetic electrodes of magnetic tunneling junctions to achieve high tunneling magnetoresistance.

Effect of Cr substitution for Fe on the spin polarization of Co2CrxFe1-xSi Heusler alloys

First-principles investigation of B2 partial disordered structure, martensitic transformation, elastic and magnetic properties of all-d-metal Ni-Mn-Ti Heusler alloys

The phase stability, magnetic properties, martensitic transformation, and electronic properties of the Ni2−xMn1+x+ySn1−y system with excess Mn have been systematically investigated by the first-principles calculations. Results indicate that the excess Mn atoms will directly occupy the sublattices of Ni (MnNi) or Sn (MnSn). The formation energy (Ef) of the austenite has a relationship with the Mn content: Ef = 135.27(1 + x + y) − 293.01, that is, the phase stability of the austenite decreases gradually with the increase in Mn content. According to the results of the formation energy of austenite, there is an antiparallel arrangement of the magnetic moment between the excess and normal Mn atoms in the Ni2−xMn1+x+ySn1−y (x = 0 or y = 0) system, while the magnetic moment direction of the normal Mn atoms arranges antiparallel to that of MnNi atoms and parallel to that of MnSn atoms in the Ni2−xMn1+x+ySn1−y (x, y ≠ 0) system. The martensitic transformation occurs in some Ni2−xMn1+x+ySn1−y (x, y ≠ 0) alloys with large magnetic moments of ferrimagnetic austenite. Besides, the valence electrons tend to distribute around the Ni or MnNi atoms and mainly bond with the normal Mn atoms. The results of this work can lay a theoretical foundation for further development of the Ni2−xMn1+x+ySn1−y system as the potential ferromagnetic shape memory alloys. 

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Phase Stability, Magnetic Properties, and Martensitic Transformation of Ni_2−xMn_1+x+ySn_1−y Heusler Alloy with Excess Mn by First-Principles Calculations

In order to explore the novel Ni-Mn-Ti-based all- d -metal Heusler alloy, the martensitic transformation, mechanical and magnetic properties of the Ni 2- x Cu x Mn 1.5 Ti 0.5 ( x = 0, 0.125, 0.25, 0.375, and 0.5) alloys and (Ni 2- x Cu x Mn 1.5 Ti 0.5 ) 0.97 B 0.03 ( x = 0, 0.125, 0.25, and 0.375) alloys were systematically investigated by the first-principles calculations. The austenite and non-modulated martensite always present an antiferromagnetic state in the investigated series. The phase stability of the austenite and martensite decreases with the increasing Cu content. Cu and B co-doping can decrease the thermal hysteresis of the Ni-Mn-Ti alloy. Doping B impedes the martensitic transformation of the Ni-Cu-Mn-Ti alloy and reduces the anisotropy of Ni-(Cu)-Mn-Ti alloy. The elastic constants of the Ni-Cu-Mn-Ti-(B) alloy were calculated, which reveals that the Ni-Cu-Mn-Ti alloy possesses great ductility and Ni-Cu-Mn-Ti-B alloy has great incompressibility, shear resistance, and normal stress resistance. The root of the martensitic transformation, mechanical and magnetic properties were discovered according to the electronic density of states. 

Martensitic transformation, mechanical and magnetic properties of Ni-Cu-Mn-Ti-(B) Heusler alloys by first-principles investigations

Perpendicular magnetic anisotropy in nearly fully compensated ferrimagnetic Heusler alloy Mn 0.75 Co 1.25 VIn: An ab initio study

Structural, electronic and magnetic properties of the Heusler alloy Mn2VIn have been investigated using the density functional theory and experimental techniques. Unlike many other Heusler compounds, Mn2VIn is not predicted to be half-metallic at the optimized lattice constant, but is highly spin polarized at a slightly lower lattice constant. It however exhibits ferrimagnetic coupling between the Mn and V sublattices, as expected of Mn-based Heuslers. We have, then, synthesized the compound by arc melting and studied magnetic properties that are of interest fundamentally and for technological applications. The structural properties were determined using X-ray diffraction, revealing the presence of cubic and tetragonal phases in the sample. The chemical composition was determined using energy-dispersive X-ray spectroscopy together with the scanning electron microscope, and the magnetic properties were investigated by superconducting quantum interference device magnetometry. The alloy exhibits superparamagnetic spin blocking with a blocking temperature $T_{B}$ of 40 K.

Zipporah W. Muthui

Papers

Perpendicular magnetic anisotropy in nearly fully compensated ferrimagnetic Heusler alloy Mn 0.75 Co 1.25 VIn: An ab initio study

Structural, Electronic and Magnetic Properties of the Heusler Alloy Mn 2 VIn: A Combined DFT and Experimental Study