Tunnel Magnetoresistance in Self-Assemblies of Exchange-Coupled Core/Shell Nanoparticles

Abstract

We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core/shell Fe 3 O 4 /Co 1−x Zn x Fe 2 O 4 nanoparticles (0 ≤ x ≤ 1). Adjusting the magnetic anisotropy through the content of Co 2+ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft/hard and hard/soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response. * winkler@cab.cnea.gov.ar 1 arXiv:2005.10771v1 [cond-mat.mes-hall] 21 May 2020

Adjusting the Néel relaxation time of Fe3O4/Zn x Co1−x Fe2O4 core/shell nanoparticles for optimal heat generation in magnetic hyperthermia

“…This result indicates a decrease of the effective magnetic anisotropy K eff of the core/shell samples with the Zn fraction, as was already found in similar nanomaterials. [32,33] The magnetization inversion process of Fe 3 O 4 /Zn x Co 1-x Fe 2 O 4 core/shell nanoparticles can be analyzed from the theoretical approach developed for bi-magnetic soft/hard exchange-coupled nanostructures, assuming a rigid magnetic coupling at the interface between the core and the shell; within this approximation the coercive field results: [30,31,33,[41][42][43] (3) where M S is the magnetization saturation of each phase (c = core and sh = shell), is the volume fraction and K eff is the effective magnetic anisotropy of the core (c) and shell (sh). According to this model the H C can be estimated for a core/shell particles from the core parameters M S = 90 emu/g, <D core > = 8.5 nm, = 3x10 5 erg/cm 3 , [28] and shell parameters as thickness of 1 nm, = 6x10 6 erg/cm 3 or 5x10 4 erg/cm 3 for the CoFe 2 O 4 [44] and ZnFe 2 O 4 [45] phases, respectively; resulting in H C = 6.4 kOe and H C = 0.4 kOe, respectively.…”

Spin‐ and Stress‐Depending Electrical Transport in Nanoparticle Supercrystals: Sensing Elastic Properties of Organic Tunnel Barriers via Tunneling Magnetoresistance

“…In these TMR devices, typically, an inorganic metal oxide layer with a thickness of 0.5 to 2 nm is chosen as an insulating barrier. Moreover, different organic barriers were studied concerning their electric behavior [2][3][4][5] , transport mechanism [6][7], and efficiency. [8][9] Especially, oleic acid as one of the most commonly used chemical for surface functionalization of nanoparticles has been investigated as potential barrier material in granular films.…”

Shell-mediated control of surface chemistry of highly stoichiometric magnetite nanoparticles

“…Magnetite (Fe 3 O 4 ) and maghemite (γ-Fe 2 O 3 ) have been approved, for example, as agents for medical imaging, magnetic fluid hyperthermia and drug delivery systems [1][2][3][4][5] . At the same time, self-assembled Fe 3 O 4 nanoparticles (NPs) and thin films have attracted attention in the field of spin-dependent electronic transport for the design of novel magnetoresistive devices [6][7][8][9][10][11][12][13] , in which the half-metallic nature and the spinpolarization of Fe 3 O 4 play a central role. However, most nanomaterials contain variable amounts of Fe 3 O 4 and γ-Fe 2 O 3 due to the relatively easy oxidation of Fe 2+ to Fe 3+ under environmental conditions [14][15][16][17] .…”