Cooling‐field dependence of exchange bias and asymmetric reversal modes in a nanoparticles system with ferromagnetic core and antiferromagnetic matrix morphology

Abstract

Interest in exchange bias (EB) in magnetic nanoparticles has increased in the past few years by virtue of its potential for application in fields such as ultrahigh-density magnetic recording. A modified Monte Carlo Metropolis method is performed to simulate the effect of cooling field on EB and asymmetric reversal modes of a granular system of ferromagnetic (FM) nanoparticles embedded in an antiferromagnetic (AFM) matrix, based on three-dimensional classical Heisenberg model. The results show that the EB first decreases slightly due to the energy barriers in the antiferromagnet, while the coercivity and vertical magnetization shift increase with the increase of cooling field, finally, they all level off as the cooling field is strong enough. Whereas the cooling-and measuring-field angular dependence of asymmetric reversal modes reveal asymmetric reversal mechanism and interesting rotation process of FM spins, confirming the existence of the net magnetization on the surface of AFM matrix. The reason may be due to the energy competition and geometric frustration of system. However, the strong interfacial coupling may change the intrinsic atomic configuration of antiferromagnet to influence the EB and reversal modes.

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

“…Computer simulations based either on MC methods or on the micromagnetic approach have proved useful to gain insight into the microscopic origin of EB 23, 24, 29. In the conventional MC Metropolis method, the flipping probability of a single moment is only determined by the energy difference between trial and original states 30.…”

“…In our previous work 15, 23, we have focused on the influence of cooling field strength and direction on EB in the conventional FM core/AFM matrix system. We have found that the existence of positive or negative EB is strongly dependent of the net magnetization on the surface of AFM matrix.…”

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

“…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.…”

Exchange bias in a nanogranular system with competing ferromagnetic and antiferromagnetic exchange interactions

“…Recently, Dong et al 20 found that in nanosized AFM manganites, the reduction in the superexchange interactions on the surface layer allows the formation of a FM shell, resulting in a natural AFM/FM interface. Furthermore, in previous work, our group has studied the field‐cooling dependence of EB in the conventional FM‐nanoparticle–AFM‐matrix systems 21, 22, the component‐ratio dependence of blocking temperature and EB in the FM–AFM random alloys 23, 24, and the effects of H FC and FM‐shell shape on EB in the nanoparticles with inverted FM–AFM core–shell morphology 25, 26, respectively. Obviously, different morphologies may induce distinct EB behaviors.…”