Exchange bias and vertical shift in CoFe2O4 nanoparticles

Abstract

Magnetic properties of core-shell cobalt ferrite nanoparticles 15 to 48nm prepared by a sol-gel route have been studied. It is shown that the coercivity follows non-monotonic size dependence varying as 1/d above the maximum (d is the particle size). Field cooled magnetization exhibited both horizontal (exchange bias) and vertical shifts. The exchange bias is understood as originating at the interface between a surface region with structural and spin disorder and a core ferrimagnetic region. The dependence of the exchange bias and vertical shifts on the particle sizes and cooling fields are found to have significant differences and the differences are explained in the light of recent results which suggest that both weakly and strongly pinned spins are present at the interface. It is suggested that the exchange bias is dominated by the weakly pinned spins while the vertical shift is affected by the strongly pinned ones. PACS Number(s): 75.75.+a, 75.50.Tt, 75.70.Cn

Synthesis and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles prepared by wet chemical route

“…Smaller and uniformly disturbed particles were obtained if the nucleation rate was higher than the growth rate. Large pH values in the range (11)(12)(13)(14) were used in accordance with predictions where high production yields are expected for large pH values. The advantage of this method over the others is that the control of production of ferrite particles, its size and size distribution is relatively easy and there is no need of extra mechanical or microwave heat treatments.…”

“…These aspects shall be discussed in detail elsewhere [14]. The magnetization of different size nanoparticles is shown as a function of temperature in Fig.…”

Effect of temperature on the exchange bias in naturally oxidized Ni Co1− (x= 0.2) nanowires fabricated by electrochemical deposition technique

“…7 shows ␦M as a function of temperature which shows that ␦M is zero above 150 K while it is maximum (∼7 × 10 5 emu) at ∼150 K, and then decreases with decreasing temperature to ∼3 K. The positive shift of ␦M in our case indicates the positive spins interactions at the interface between the two magnetic media (FM core and AFM shell). The presence of vertical shift accompanying the exchange bias is generally associated with uncompensated pinned spins present at the core-shell interface [9]. We assume that in case of core/shell nanowires the high temperatures enable more of the interfacial spins to become decoupled from the AFM shell and be pinned with the interface in the direction close to the applied field, thereby increasing the vertical shift at 150 K, similar to the case of core/shell nanoparticles reported earlier [9].…”

“…H ex has also been observed in other bilayer systems involving ferromagnetic, ferrimagnetic, and spin glass (SG) like materials [5,6]. This phenomenon has been investigated mainly in thin films and nanoparticles [7][8][9]. However, this effect has been recently observed in nanowires as well [10,11].…”

Giant vertical magnetization shift induced by spin canting in a Co/Ca2Ru0.98Fe0.02Yuan1, Li2, Qi3 et al. 2013Phys. Rev. B282120View full textAdd to dashboardCite

“…A VMS has been observed frequently [5][6][7][8][9][10][11][12][13][14][15][16] , and could originate from any of several proposed mechanisms. Among them, the Meiklejohn-Bean model predicts that an AFM monolayer at the interface with the FM layer is uncompensated, but still remains part of the AFM lattice 1, 3 .…”