Exchange Bias in Cr₂O₃/Fe₃O₄Core/Shell Nanoparticles

Size-Dependent Passivation Shell and Magnetic Properties in Antiferromagnetic/Ferrimagnetic Core/Shell MnO Nanoparticles

“…6,[9][10][11] Recently, "inverse" core/shell nanoparticles, with AFM cores and FiM or spin-glass shells, have been synthesized, leading to a number of novel magnetic properties. [34][35][36][37][38][39][40][41][42][43][44][45][46] In particular, the magnetic properties of inverse core/shell nanoparticles based on the passivation of AFM MnO nanoparticles have been investigated. [34][35][36][37][38]40 These materials exhibit novel properties at low temperatures [34][35][36][37]40 such as very large exchange bias and coercivity with a nonmonotonic dependence on the core diameter 34 and spontaneous magnetization and ferrimagnetic order above the Curie temperature of the shell.…”

“…Special types of magnetic nanoparticles are core/shell nanoparticles. Although in most cases the shell serves just for protection purposes, the study of bimagnetic nanoparticles, where both the shell and the core are magnetic, is steadily increasing. ,− In fact, the shell properties and exchange coupling between the core and the shell open new degrees of freedom to tailor the overall properties of the nanoparticles, leading to novel applications (such as enhanced coercivity and energy products, tunable blocking temperatures, improved electromagnetic radiation absorption, and hyperthermia treatment). ,,− Core/shell nanoparticles with a FM (or FiM) core and a AFM (or FiM) shell have been widely investigated. ,− Recently, “inverse” core/shell nanoparticles, with AFM cores and FiM or spin-glass shells, have been synthesized, leading to a number of novel magnetic properties. − In particular, the magnetic properties of inverse core/shell nanoparticles based on the passivation of AFM MnO nanoparticles have been investigated. − , These materials exhibit novel properties at low temperatures − , such as very large exchange bias and coercivity with a nonmonotonic dependence on the core diameter and spontaneous magnetization and ferrimagnetic order above the Curie temperature of the shell. − However, in these nanoparticles, although the shell material is usually identified as Mn 3 O 4 , ,− , it has been recently shown that γ-Mn 2 O 3 can also be formed as a result of MnO passivation …”

Enhanced Magnetic Properties in Antiferromagnetic-Core/Ferrimagnetic-Shell Nanoparticles

“…Interestingly, currently, there is an increasing interest in, so-called, inverted structures (see Fig. 1), where the shell is FM or ferrimagnetic (FiM) and the core is AFM, containing for example Mn oxides12131415161718, Fe oxides1920212223242526272829, Co oxides30313233343536, Cr oxides373839, metallic FePt40 or even multiferroic BiFeO 3 (Refs. 41,42).…”

“…It has been demonstrated, experimentally and theoretically, that the poor crystallinity of the AFM counterpart can result in considerably inferior exchange bias properties4344. In fact, inverted structures have already demonstrated very large coercivities and loop shifts, tunable blocking temperatures, enhanced Néel temperatures or proximity effects12131415161718192021222324252627282930313233343536373839404142 and have been proposed as potential magnetoelectric random access memories41. However, despite their potential, systematic studies of size effects (i.e., core diameter or shell thickness) are still rather scarce12162225333435.…”