Size and surface effects in the magnetic order of CoFe2O4 nanoparticles

Pianciola, B; Lima, Enio; Troiani, Horacio Esteban; Nagamine, L.C.C.M.; Cohen, Renato; Zysler, R.D.

doi:10.1016/j.jmmm.2014.10.054

Cited by 34 publications

(17 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The effective hyperfine fields calculated via our geometrical model: H HYP 2 = H EFF 2 + H APP 2 ± 2 H APP H HYP cos(θ) are close to the hyperfine fields determined from the zero‐field spectra distributions, reflecting the consistency of the analysis. Such non‐collinear spin structure has already been investigated in other systems and, interestingly, in our case no major differences between samples TD9 and SV7 can be noticed, even if their magnetic anisotropy is different. The canting between the magnetic sublattices is slightly larger for TD9, while A and B sublattices are almost aligned for SV7.…”

Section: Resultssupporting

confidence: 71%

Internal Structure and Magnetic Properties in Cobalt Ferrite Nanoparticles: Influence of the Synthesis Method

Lavorato

Alzamora

Contreras

et al. 2019

Part & Part Syst Charact

View full text Add to dashboard Cite

The design of novel nanostructured magnetic materials requires a good understanding of the variation in the magnetic properties due to different synthesis conditions. In this work, four different procedures for fabricating Co‐ferrite nanoparticles with similar sizes between 7 and 10 nm are compared by studying their structural and magnetic properties. Non‐aqueous methods based on the thermal decomposition of metal acetylacetonates at high temperatures, either with or without surfactants, provide highly crystalline nanoparticles with large saturation magnetization values and a coherent reversal of the magnetic moment. However, variations in the density of defects and in the shape of the nanocrystals determine the distribution of switching fields and the effective magnetic anisotropy, which reaches up to ≈1 × 107 erg cm−3 for oleic acid‐capped 9 nm nanoparticles. It is shown that the saturation magnetization values for nanoparticles produced by different methods are in the range between 49 and 95 emu g−1 due to differences in the stoichiometry, in the cation occupancy, in the magnetic disorder and in the spin canting of the magnetic sub‐lattices, the latter evaluated by in‐field Mössbauer spectroscopy.

show abstract

Section: Resultssupporting

confidence: 71%

Internal Structure and Magnetic Properties in Cobalt Ferrite Nanoparticles: Influence of the Synthesis Method

Lavorato

Alzamora

Contreras

et al. 2019

Part & Part Syst Charact

View full text Add to dashboard Cite

show abstract

“…Therefore, the coercivity decreases with increasing concentration of NiFe 2 O 4 [19]. These phenomenon also observed for the BaFe 12 O 19 /CoFe 2 O 4 [11], BaFe 12 O 19 /NiZnFe 2 O 4 [4] and SrFe 12 O 19 /CoFe 2 O 4 [10]. Meanwhile, the decrease in saturation magnetization can be also explained based on grain size, particles distribution, spin canting, and impurity The magnetic parameters such as M, M r and H C of nanocomposite samples with different R V are higher than those of nanocomposite samples with different R m .…”

Section: Resultssupporting

confidence: 64%

“…However, the magnetic properties of the ferrite composite powders are highly sensitive to grain size, microstructure, distribution of the magnetically hard and soft phases, as well as impurity [4]. Therefore, to achieve highly homogeneous ferrite particles, low-temperature chemical methods have been used, such as hydrothermal [8,9], sol-gel [10,11]. Moreover, the ferrites can be successfully synthesized at a relatively low temperature without sintering at high temperatures, which may be beneficial to control the growth of crystallites.…”

Section: Introductionmentioning

confidence: 99%

Fabrication and Magnetic Properties of Sintered SrFe$_{12}$O$_{19}$-NiFe$_{2}$O$_{4}$ Nanocomposites

Nga¹,

Loan²

2017

Comm. in Phys.

View full text Add to dashboard Cite

Two series of SrFe$_{12}$O$_{19}$/NiFe$_{2}$O$_{4}$ nanocomposite ferrites sintered in air at 850\rc{}C and 950\rc{}C were prepared using SrFe$_{12}$O$_{19}$ and NiFe$_{2}$O$_{4}$ nanopowders obtained via sol-gel method. The phase composition, surface morphology and magnetic properties of the composites were investigated using XRD, SEM and VSM respectively. For the SrFe$_{12}$O$_{19}$/NiFe$_{2}$O$_{4}$ ferrites with volume ratio ranging from 61 to 21 and sintered in 850$\r{}$C for 5 hours in air, all the specimens are composed of two phases but exhibit a typical single-phase magnetic behavior, indicating the existence of exchange coupling (EC) between the magnetically hard and soft phases. The value of coercivity H$_{c}$ decreases from 6.19 kOe to 0.574 kOe when volume of SrFe$_{12}$O$_{19}$ decreases from 6 to 1. While the samples with a mass ratio of $R_{m}$= SrFe$_{12}$O$_{19}$/ NiFe$_{2}$O$_{4}$ varying from 31 to 13 sintered in 950\rc{}C for 5 hours characterized with a ``bee waist'' type hysteresis loop. These results reveal that the magnetically hard and soft magnetic phases are not exchange- coupled. The saturation magnetization ($M_{S}$) increases from 36 emu/g to 43.3 emu/g when $R_{m}$ decreases from 31 to 13 and then decreases with $R_{m}= 12$ and 13.

show abstract

“…The large magnetic surface disorder of the FiM shell is reflected in the M S reduction with temperature and in the relatively low H C compared to single-phase CoFe 2 O 4 NPs, whose low-temperature H C was found to be between 10 and 18 kOe. [57][58][59][60] In addition, viscosity measurements suggest that the activation or switching volume is nearly a third of the total shell volume, even if the total volume is lower than the critical single-domain volume. Such results evidence the importance of local effects, e.g.…”

Section: Magnetic Relaxation and Activation Volumesmentioning

confidence: 99%

Magnetic Interactions and Energy Barrier Enhancement in Core/Shell Bimagnetic Nanoparticles

et al. 2015

Self Cite

View full text Add to dashboard Cite

In this work, we studied the dynamic and static magnetic properties of ZnO-core/CoFe 2 O 4 -shell and CoO-core/CoFe 2 O 4 -shell nanoparticles. Both systems are formed by a core of ∼4 nm of diameter encapsulated in a shell of ∼2 nm of thickness. The mean blocking temperature changes from 106(7) to 276(5) K when the core is diamagnetic or antiferromagnetic, respectively. Magnetic remanence studies revealed the presence of weak dipolar interparticle interactions, where H int is approximately −0.1 kOe for ZnO/ CoFe 2 O 4 and −0.9 kOe for CoO/CoFe 2 O 4 , playing a minor role in the magnetic behavior of the materials. Relaxation experiments provided evidence that the magnetization reversal process of CoFe 2 O 4 is strongly dependent on the magnetic order of the core. At 10 K, activation volumes of ∼46(6) and ∼69(5) nm 3 were found for CoO/CoFe 2 O 4 and ZnO/CoFe 2 O 4 nanoparticles, respectively, corresponding to one-third and one-fifth of the total shell volume. While the magnetic behavior of ZnO/CoFe 2 O 4 nanoparticles is strongly affected by the surface disorder, the exchange coupling at the CoO/CoFe 2 O 4 interface rules the magnetization reversal and the nanoparticles' thermal stability by inducing a larger energy barrier and promoting smaller switching volume.

show abstract

Size and surface effects in the magnetic order of CoFe2O4 nanoparticles

Cited by 34 publications

References 27 publications

Internal Structure and Magnetic Properties in Cobalt Ferrite Nanoparticles: Influence of the Synthesis Method

Internal Structure and Magnetic Properties in Cobalt Ferrite Nanoparticles: Influence of the Synthesis Method

Fabrication and Magnetic Properties of Sintered SrFe\(_{12}\)O\(_{19}\)-NiFe\(_{2}\)O\(_{4}\) Nanocomposites

Magnetic Interactions and Energy Barrier Enhancement in Core/Shell Bimagnetic Nanoparticles

Contact Info

Product

Resources

About