Microwave electromagnetic and absorption properties of Nd2Fe14B∕α-Fe nanocomposites in the 0.5–18 and 26.5–40GHz ranges

Abstract

Nd 2 Fe 14 B ∕ α - Fe nanocomposites were prepared using a melt-spinning method, subsequent annealing treatment, and ball milling. The complex permittivity and permeability of the composites were measured in the 0.5–18 and 26.5–40GHz frequency ranges. The permeability spectra of the Nd2Fe14B∕α-Fe nanocomposites exhibit relaxation and resonance type characteristic in the 0.5–18 and 26.5–40GHz frequency ranges, respectively. The resonance frequency (fr) of Nd10Fe78Co5Zr1B6 nanocomposite is 30GHz due to the large anisotropy field (HA). However, the resonance frequency of the Nd2Fe14B∕α-Fe sample is lower than that of Nd2Fe14B, due to the decrease of HA induced by the exchange interaction between hard and soft magnetic phases. These samples also showed good microwave absorption performance (reflection loss: <−20dB) in 9, 17, and 35–38GHz with matching thicknesses of 2, 1.2, and 0.37mm, respectively. Therefore, Nd2Fe14B∕α-Fe nanocomposites are thought to be a potential candidate for thinner microwave absorbers not only in the centimeter wave but also in the millimeter wave band.

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

“…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].…”

“…Moreover, the patents on core/shell nanoparticles and the studies on nanocomposite materials (i.e., not core/shell) have also shown that other hard materials may be potentially interesting as reflection loss materials, e.g. 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.…”

“…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].…”

Generalization of Snoek’s law to ferromagnetic films and composites

“…For a film with perfect orientation and limited skin Crit_skin_LL31.doc p. 7 28/11/2007 effect, this quantity represents the saturation magnetization :…”

“…High frequency inductors, 1 magnetic recording write heads, broadband skin antennas, 2 microwave filters, 3,4 noise suppressors 5 and Radar Absorbing materials 6,7 require high broadband permeability levels at elevated frequencies. However, it has been known since the work of Snoek 8 that there exist tradeoffs between high permeability levels and operation at elevated frequencies, i.e.…”