Electromagnetism and magnetization in granular two-phase nanocomposites: A comparative microwave study

Abstract

Electromagnetic and magnetic properties of multicomponent metal oxides heterostructures: Nanometer versus micrometer-sized particles J. Appl. Phys. 93, 9243 (2003); 10.1063/1.1570935Influence of cobalt and nickel substitutions on populations, hyperfine fields, and hysteresis phenomenon in magnetite Cold-pressed powder compacts in our experiments were prepared from commercial nanopowders of ZnO, Ni, Co and ␥-Fe 2 O 3 . A systematic study of the room temperature effective permeability tensor of composite samples made of these nanophases is performed and provides a signature for the nonreciprocity of wave propagation in these nanostructures. Our measurements which cover a broad range of frequency in the microwave region provide a wealth of information leading to a much better understanding of the electromagnetic wave transport in nanogranular materials throughout this frequency range. We report our observations on the frequency and composition dependences of the permeability tensor components of a large set of nanocomposites ͑NCs͒ at different magnetic fields. It is found that mixing Ni nanoparticles with ZnO nanoparticles results in a smaller linewidth of the gyromagnetic resonance and an increased coercivity compared to a sample consisting solely of Ni nanoparticles. On the contrary, mixing of Co nanoparticles with ZnO nanoparticles resulted in the disappearance of the off-diagonal component of the permeability tensor and an increase in coercivity. Deviations of the saturation magnetization of Ni and Co in the Ni/ ZnO and Co/ ZnO NCs from bulklike values were observed. It is believed that the different microwave magnetic behaviors of the Ni/ ZnO and Co/ ZnO NCs are related to the difference in magnetic anisotropy of the Ni and Co particles. It is argued that surface and boundaries in the samples can play a significant role in the microwave magnetic response of these nanostructures. These NCs are promising for implementing the nonreciprocal functionality employed in many microwave devices, including isolators and circulators.

Broadband Ferromagnetic Resonance Measurements in Ni/ZnO and Niγ-Fe2O3Nanocomposites

“…As part of a large effort to quantitatively model the electromagnetic transport properties in nanostructures, we have recently investigated on the microwave properties of NCs containing Ni, Co, ZnO, and γ-Fe 2 O 3 nanoparticles [15][16][17][18][19][20][21][22][23]. For these epoxy-coated particles, the distance of closest approach between particles is expected to be large enough for the interactions to have mainly a magnetostatic character [20].…”

“…Theoretical interest is also motivated by the suggestion that surface magnetic interactions and surface disorder can greatly enhance the effective magnetic properties of nanostructures, for example, coercivity as a consequence of the reduced crystal symmetry near the surface originating from the finite size and possible existence of surface disorder [24][25][26][27][28]. In particular, the set of compounds Ni/γ-Fe 2 O 3 and Ni/ZnO have proven fertile to study in order to examine the interplay between magnetic metal and semiconductor oxide as γ-Fe 2 O 3 is substituted into the ZnO member [20,22], which has been seen to occur in a wide variety of granular nanostructures. These nanostructures provide an ideal playground to experimentally investigate some fundamental phenomena connected with interparticle interactions because the specific surface area of γ-Fe 2 O 3 nanoparticles is more than three times that of Ni (see Table 1) causing the magnetic boundaries to strongly interact.…”

Spin wave spectroscopy and microwave losses in granular two-phase magnetic nanocomposites

“…Phys. 101, 034320 ͑2007͒ regions, specifically the formation of an antiferromagnetic ͑NiO͒ oxide layer around the ferromagnetic core of the Ni particles for the nNiZ series and a ferromagnetic layer NiFe 2 O 4 for the nNiF series, 24,28 and the sample inhomogeneity. Our results are reminiscent of those recently observed 27 of a double-peak behavior in the imaginary part of the effective magnetic permeability, and which was attributed to both the polydispersity and the dynamic magnetic inhomogeneity of the samples, e.g., excess spins in oxide layers.…”

“…4,21,22 Enhanced electromagnetic properties at microwave frequencies have recently been achieved with Ni/ ␥-Fe 2 O 3 NCs. [23][24][25][26][27][28] When a͒ Author to whom correspondence should be addressed; also at Département de Physique, Université de Bretagne Occidentale; electronic mail: brosseau@univ-brest.fr compared to the zero-field case, the field measurements of the permeability tensor exhibit nonzero off-diagonal components giving evidence of the nonreciprocity of wave propagation in these nanostructures. These experimental results were analyzed within a recently developed multiscale modeling 4 and can be understood as arising from magnetostatic intergranular interactions via a mean-field approximation.…”

“…Our previous studies 4, [23][24][25][26][27][28] were focused on the determination of the effective material parameters ͑complex permittivity and permeability and effective Gilbert damping parameter͒ in the EMA and the evaluation of the magnetization of these NCs. In the current investigation, we evaluate the microwave properties of selected NCs by combining the microstrip line method and the SWS method.…”