The carbon-coated Ni(C) nanocapsules were prepared by a modified arc-discharge method in methane atmosphere. Its electromagnetic parameters were measured at 2–18GHz. It is observed that the natural resonance which appeared at 5.5GHz is dominant among microwave absorption properties of Ni(C) nanocapsules, as the consequence of the increased surface anisotropic energy for nanosized particles. The measured relative complex permittivity indicates that a high resistivity existed in Ni(C) nanocapsules samples. The maximum reflection loss of Ni(C) nanocomposites can reach 32dB at 13GHz with 2mm in thickness. The microwave absorptive mechanisms of Ni(C) nanocapsule absorbent were discussed.

We present the dependence of the magnetostriction in Ni 0.8 Fe 0.2 films on Tb and Gd doping concentration and compare with the measured doping dependence of the high-frequency damping. While the magnetostriction and the high-frequency damping are correlated, the dependence is complicated. In particular, the high-frequency damping parameter ␣ increases rapidly (␣ ϭ0.008-0.84) with a modest increase in the magnetostriction ͑ s ϭϪ0.6ϫ10 Ϫ6 to 5.7ϫ10 Ϫ6 ͒ for Tb doping concentrations up to 10%. For Gd doping, the high-frequency damping changes slowly ͑␣ϭ0.008 -0.02͒ as the doping concentration is increased to 10%, whereas the increase in magnetostriction is similar to that observed in the Tb-doped films. Further, it is possible to achieve low magnetostriction ( s ϭ2ϫ10 Ϫ6 ) near the region of critical damping. Measurements of the angular dependence of the ferromagnetic resonance linewidth in Tb-doped Ni 0.8 Fe 0.2 films show little change similar to the behavior observed in undoped Ni 0.8 Fe 0.2 films, although the linewidths are considerably larger. This is in contrast to systems such as Ni 0.8 Fe 0.2 on NiO, which have a large angular dependence indicating that the relaxation process proceeds through the generation of spin waves. The enhanced damping in the Tb-doped films appears, therefore, to be mediated through direct phonon generation.

Articles you may be interested inCrystal structure and magnetic properties of Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics using neutron diffraction and Mossbauer spectroscopy AIP Advances 4, 087121 (2014); 10.1063/1.4893241Effect of Pr-and Nd-doping on structural, dielectric, and magnetic properties of multiferroic Bi0.8La0.2Fe0.9Mn0.1O3Polycrystalline multiferroic La 0.8 Bi 0.2 Fe 1−x Mn x O 3 ͑0.0Յ x Յ 0.4͒ samples were synthesized by the conventional solid state reaction method. Reitveld refinement of the x-ray diffraction patterns confirms the single phase character of all the compositions with orthorhombic structure having space group Pnma ͑No. 62͒. Dielectric properties of the samples at temperatures 200-475 K and frequencies 500 kHz-1 MHz authenticate the stabilization of ferroelectric phase with Mn substitution. Dielectric responses of these multiferroics have been analyzed carefully, in the light of "universal dielectric response" model. While cooling from room temperature to 20 K, systematic shifts in magnetization hysteresis loops indicate the presence of exchange bias ͑EB͒ phenomenon in the system. Magnetic behavior of these samples has been briefly discussed on the basis of "EB" model for granular systems. Temperature and magnetic field dependent magnetization data demonstrate enhanced magnetization due to the Mn substitution. Magnetocapacitance measurement reveals the magnetoelectric coupling for wide range of temperature ͑180-280 K͒ and decrease in dielectric loss at high magnetic field ͑3 T͒.

We report on the synthesis of Fe-doped ZnO with nominal composition of Zn 0.99 Fe 0.01 O by using a coprecipitation method. X-ray diffraction and selective area electron diffraction studies reveal a single phase wurtzite crystal structure without any secondary phase. Field emission transmission electron microscopy measurements infer that Zn 0.99 Fe 0.01 O have nanorod-type microstructures. Magnetic hysteresis measurement performed at different temperatures show that Zn 0.99 Fe 0.01 O exhibits a weak ferromagnetic behavior at room temperature. A detailed investigation of the electronic and local structure using O K-, Fe L 3,2 near edge x-ray absorption fine structure suggests that Fe is substituting Zn in ZnO matrix and is in Fe 3+ state.

We report structural, magnetic and electronic structure studies of pure and Cu doped ZnO nanorods with the aim to understand the origin of ferromagnetism. A structural study indicates that all the samples exhibit single phase nature and rules out the formation of secondary phase. NEXAFS measurements reveal that Cu ions exist in Cu 2+ state. Magnetic hysteresis loop measurements reflect that the pure and Cu doped ZnO nanorods exhibit room temperature ferromagnetism. The increase in the intensity of green emission in photoluminescence study indicates that defects density increases with Cu doping.In the recent years dilute magnetic semiconductors (DMS) has attracted the interest of researchers due to their potential application in spintronics devices. 1-3 Initially, it was assumed that DMS and their properties can be tailored by partial replacement of cations in semiconducting host matrix via transition metal (TM) cations. But the discovery of the unexpected magnetism in HfO 2 , 4 TiO 2 , 5 ZnO, 6 etc. has triggered a debate on the origin of ferromagnetism in the DMS. Several experimental as well as theoretical groups have reported the origin of ferromagnetism in the nanoparticles or thin films of diamagnetic oxides. Though, among the diamagnetic oxides showing the d 0 ferromagnetism, zinc oxide (ZnO) has been recognized as one of the most important materials for the application in the multifunctional devices because of its various properties.Even though ferromagnetism has been observed in a number of systems, experimental studies on TM doped ZnO have produced inconsistent results and the mechanism of * , † Corresponding Authors. ferromagnetism (FM) in TM doped ZnO remains unclear. It is considered that the TM dopants in ZnO form clusters or secondary phase, therefore, having many controversies about whether the observed FM is an intrinsic or extrinsic property of the material. These facts motivated us to study the FM in Cu doped ZnO. As it is well known that Cu is a potential magnetic ion only in +2 state with +1/2 spin and neither metallic Cu nor its oxide (CuO and Cu 2 O) is ferromagnetic. In these circumstances, Cu doped ZnO has potential of showing magnetic behavior at RT because FM observed in Cu based system will undoubtedly be the intrinsic property of the material. Despite the above fact, Cu doped ZnO system is not far away from controversies. There are many contradictory reports in which some authors confirmed the presence of FM in this system whereas others ruled out same. 7-10 These controversial results indicate that FM in DMSs is very sensitive to preparation method and conditions.In this letter, we have reported room temperature ferromagnetism in Cu doped ZnO synthesized by co-precipitation 17 Funct. Mater. Lett. 2011.04:17-20. Downloaded from www.worldscientific.com by PENNSYLVANIA STATE UNIVERSITY on 03/14/15. For personal use only.