Effect of cooling field strength and ferromagnetic shell shape on exchange bias in nanoparticles with inverted ferromagnetic–antiferromagnetic core‐shell morphology

Abstract

The dependence of exchange bias (EB) effects on cooling field strength and particle shape in nanoparticles with antiferromagnetic (AFM) interfacial coupling and inverted AFM core with a fixed radius and ferromagnetic (FM) shell with various thicknesses are investigated by using a modified Monte Carlo Metropolis method. It is found that with the increase of cooling field, field-cooled exchange bias field (H E ) fluctuates in the range of negative values initially, and then has an abrupt jump from the negative value to the positive value, finally levels off. However, H E decreases as the FM shell shape varies from No. 1 to No. 13 regardless of the strength of cooling field. Coercivity is affected by cooling fields and shapes indicating distinct behaviors. Because the AFM core is almost unaffected by shape and frozen completely during measuring hysteresis loops, the effect of ferromagnets on EB, negligible in most of other systems, is ambiguously manifested in such an unconventionally structural system. Moreover, the phenomena are interpreted well by presenting the snapshots of microscopic spin energy distributions, which make us observe directly and vividly the movement of domains and the competition of energies. This work will shed new light into the microscopic origin of peculiar magnetic properties of nanoparticles with special structures.

An effective-field theory study of hexagonal Ising nanowire: Thermal and magnetic properties

“…Moreover, the hysteresis loops decrease as the temperature increases. These results are consistent with some experimental [62][63][64][65][66][67][68] and theoretical results [54,56,69,70].…”

“…Theoretically, magnetic properties of nanomaterials have been studied by various techniques such as variational cumulant expansion (VCE) [17,18], Green functions (GF) formalism [19], mean field theory (MFT) [20][21][22][23][24][25][26], effective field theory (EFT) with correlations [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42], and Monte Carlo (MC) simulations [43][44][45][46][47][48][49][50][51][52][53][54][55][56][57][58]. From these studies we see that the core-shell structure can be successfully perform to nanomagnetism for nanomaterials.…”

Investigation of bond dilution effects on the magnetic properties of a cylindrical Ising nanowire

“…On the theoretical side, much effort has also been devoted, and these systems have been studied by a wide variety of techniques such as mean field theory (MFT) [17][18][19][20][21][22][23], effective field theory (EFT) with correlations [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35], Green functions (GF) formalism [36], variational cumulant expansion (VCE) [37,38], and Monte Carlo (MC) simulations [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54]. Monte Carlo simulation [55] is regarded as a powerful numerical approach for simulating the behavior of many complex systems, including magnetic nanoparticle systems.…”

“…For instance, by utilizing this tool, Refs. [39][40][41][42][43][44][45][46][47][48][49][50] investigated the exchange bias effect in magnetic core-shell nanoparticles where the hysteresis loop exhibits a shift below the Neél temperature of the antiferromagnetic shell due to the exchange coupling at the interface region of ferromagnetic core and antiferromagnetic shell. Furthermore, according to recent Monte Carlo studies, it has been shown that the core-shell concept can be successfully applied in nanomagnetism since it is capable of explaining various characteristic behaviors observed in nanoparticle magnetism [51][52][53][54].…”

Origins of the Exchange-Bias Phenomenology, Coercivity Enhancement, and Asymmetric Hysteretic Shearing in Core-Surface Smart Nanoparticles

“…However, only very recently, some works partially addressing the numerical studies of EB effects in magnetic NPs have been published [18][19][20][21][22][23][24]. In order to understand the origin of the loop shifts displayed numerically in NPs with core-shell morphology, the researchers simulated, using the Monte Carlo (MC) technique, the atomic-scale modeling where the spins interact with nearest-neighbor Heisenberg interactions.…”