Magnetic and Microwave Absorption Properties of Core/Shell FeCo-Based Nanocomposites Synthesized by a Simple Wet Chemical Method

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

“…This stems from three main drawbacks of this method, (i) the shell is always derived from the core, consequently their sizes cannot be independently controlled (ii) since the shell phase has to be derived from a surface treatment of the core material, the possible choices of core/shell phases are somewhat limited; (iii) since the materials in the core and the shell often have quite different structural characteristics (e.g., metal vs. oxide), the structural quality of the shell may be inferior. Despite these disadvantages, several examples of this approach using surface oxidation, mainly for inverse soft/hard systems, can be found in the literature: FeCo/CoFe 2 O 4 [120,121], FeCoB/CoFe 2 O 4 [123] and FeCo(Al)/FeCo(Al)O x [124]. Concerning controlled reduction, only the CoFe 2 O 4 /FeCo system has been studied, although two different reduction approaches have been used hydrogen reduction [125][126][127][128][129] and carbon reduction [130].…”

“…Concerning controlled reduction, only the CoFe 2 O 4 /FeCo system has been studied, although two different reduction approaches have been used hydrogen reduction [125][126][127][128][129] and carbon reduction [130]. Interestingly, previous to surface treatment the nanoparticles were synthesized mainly by wet chemistry methods such as: thermal decomposition [122], metal reduction [123], sol-gel [129] or co-precipitation [126]. However, some physical approaches have been also reported to obtain the initial nanoparticles such as: inert gas condensation [120], thermal plasma method [124], flame spray pyrolysis [121] and ionic coordination [125][126][127][128].…”

“…When analyzing the magnetic properties observed experimentally for diverse hard-soft core/shell nanoparticles a spread of different behaviors can be found [91][92][93][94][95][98][99][100][102][103][104]106,107,110,111,114,115,[121][122][123][125][126][127][128][129][130][131][132]136,140,141,143,175,. First, it should be pointed out that given that we are dealing with nanoparticles the core and shell sizes are rather small (i.e., usually smaller than 2 H ), thus, most of the systems exhibit smooth hysteresis loops typical of strongly exchange coupled hard-soft counterparts.…”

“…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].…”

“…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].…”