Effect of surface pinning on magnetic nanostuctures

Sahoo, Aditi; Bhattacharya, Dipten; Mohanty, P. K.

doi:10.1103/physrevb.101.064414

Cited by 9 publications

(13 citation statements)

References 74 publications

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“…Similarly, positive EB occurred with more pinning of down spins (↓) at the CS interface. Also, in the case of FN when shell is antiferromagnetically ordered, the spin pinning is less effective and the intrinsic field produced by the system is negligible 59 . It is well known that the amount of AFM uncompensated spins at the interface totally influence the phenomenon of the EB effect 19 , 60 .…”

Section: Resultsmentioning

confidence: 99%

A comparative investigation of normal and inverted exchange bias effect for magnetic fluid hyperthermia applications

Tsopoe

Borgohain

Fopase

et al. 2020

Sci Rep

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Exchange bias (EB) of magnetic nanoparticles (MNPs) in the nanoscale regime has been extensively studied by researchers, which have opened up a novel approach in tuning the magnetic anisotropy properties of magnetic nanoparticles (MNPs) in prospective application of biomedical research such as magnetic hyperthermia. In this work, we report a comparative study on the effect of magnetic EB of normal and inverted core@shell (CS) nanostructures and its influence on the heating efficiency by synthesizing Antiferromagnetic (AFM) NiO (N) and Ferrimagnetic (FiM) Fe3O4 (F). The formation of CS structures for both systems is clearly authenticated by XRD and HRTEM analyses. The magnetic properties were extensively studied by Vibrating Sample Magnetometer (VSM). We reported that the inverted CS NiO@Fe3O4 (NF) MNPs have shown a greater EB owing to higher uncompensated spins at the interface of the AFM, in comparison to the normal CS Fe3O4@NiO (FN) MNPs. Both the CS systems have shown higher SAR values in comparison to the single-phased F owing to the EB coupling at the interface. However, the higher surface anisotropy of F shell with more EB field for NF enhanced the SAR value as compared to FN system. The EB coupling is hindered at higher concentrations of NF MNPs because of the enhanced dipolar interactions (agglomeration of nanoparticles). Both the CS systems reach to the hyperthermia temperature within 10 min. The cyto-compatibility analysis resulted in the excellent cell viability (> 75%) for 3 days in the presence of the synthesized NPs upto 1 mg/ml. These observations endorsed the suitability of CS nanoassemblies for magnetic fluid hyperthermia applications.

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Section: Resultsmentioning

confidence: 99%

A comparative investigation of normal and inverted exchange bias effect for magnetic fluid hyperthermia applications

Tsopoe

Borgohain

Fopase

et al. 2020

Sci Rep

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“…Earlier works 38,48,49 had poined out that positive exchange bias results from competition between antiferromagnetic exchange coupling across ferromagnetic/antiferromagnetic interface (i.e., negative J int ) and ferromagnetic coupling between applied field and antiferromagnetic moment at the interface. However, as shown in our earlier theoretical work 30 , neither in two-dimensional nor in threedimensional spin structure, variation of J int (including switch in J int from positive to negative) has any significant impact on the exchange bias for Ising, XY, and Heisenberg spins. The role of J int in governing the sign and magnitude of exchange bias could be significant in nanoscale core-shell structures where the core is ferromagnetic and the shell is antiferromagnetic and the measurement is carried out, primarily, under field-cooled condition.…”

Section: Resultsmentioning

confidence: 54%

“…All these results could be rationalized by resorting to the concept of surface spin pinning effect in nanoparticles 30 . Using Monte Carlo simulations, the magnetic hysteresis loops for different nanoparticle aggregate structures have been obtained.…”

Section: Resultsmentioning

confidence: 99%

“…Keeping these facts in mind, we modeled the inverse coreshell nanoparticles and their assembly in three dimension (3D). The effect of surface pinning on nanostructures, including heterostructures, has been thoroughly discussed in a recent article 30 . It was found that the change in the magnetic properties due to surface pinning is quite robust, in a sense that it is effective in both two-and threedimensional particles, and with different spin interactions such as Ising, XY, and Heisenberg.…”

Section: Theoretical Simulationmentioning

confidence: 99%

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Large structure-dependent room temperature exchange bias in self-assembled BiFeO3 nanoparticles

Goswami,

Sahoo,

Bhattacharya

et al. 2020

Preprint

Self Cite

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We studied the magnetic properties of self-assembled aggregates of BiFeO 3 nanoparticles (∼20-40 nm). The aggregates formed two different structures -one with limited and another with massive crosslinking -via 'drying-mediated self-assembly' process following dispersion of the nanoparticles within different organic solvents. They exhibit large coercivity H C (>1000 Oe) and exchange bias field H E (∼350-900 Oe) in comparison to what is observed in isolated nanoparticles (H C ∼ 250 Oe; H E ∼ 0). The H E turns out to be switching from negative to positive depending on the structure of the aggregates with | +H E | being larger. The magnetic force microscopy reveals the magnetic domains (extending across 7-10 nanoparticles) as well as the domain switching characteristics and corroborate the results of magnetic measurements. Numerical simulation of the 'drying-mediated-self-assembly' process shows that the nanoparticle-solvent interaction plays an important role in forming the 'nanoparticle aggregate structures' observed experimentally. Numerical simulation of the magnetic hysteresis loops, on the other hand, points out the importance of spin pinning at the surface of nanoparticles as a result of surface functionalization of the particles in different suspension media. Depending on the concentration of pinned spins at the surface pointing preferably along the easy-axis direction -from greater than 50% to less than 50% -H E switches from negative to positive. Quite aside from bulk sample and isolated nanoparticle, nanoparticle aggregates -resulting from surface functionalization -therefore, offer remarkable tunability of properties depending on structures.

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“…25,26 When the system is examined under eld cooling conditions, the anisotropy of AFM is expected to be modied due to the interface effect of the FiM/ AFM system, and essentially, uncompensated spins at the interface are either pinned or unpinned with respect to FiM spins. 27 Therefore, the consequence of the shi in hysteresis loop and the amplication of the coercive eld are expected to originate from the pinned and unpinned uncompensated spins of AFM at the magnetically disordered interface. When the sample is under eld cooling, unpinned spins are dragged and rotate along the eld direction providing an extra magnetization to FiM, which leads to the coercivity enhancement.…”

Section: Resultsmentioning

confidence: 99%

A temperature-dependent switching of the exchange bias effect from negative to positive under a fixed intermediate cooling field

Tsopoe

Borgohain

2021

RSC Adv.

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Effect of surface pinning on magnetic nanostuctures

Cited by 9 publications

References 74 publications

A comparative investigation of normal and inverted exchange bias effect for magnetic fluid hyperthermia applications

A comparative investigation of normal and inverted exchange bias effect for magnetic fluid hyperthermia applications

Large structure-dependent room temperature exchange bias in self-assembled BiFeO3 nanoparticles

A temperature-dependent switching of the exchange bias effect from negative to positive under a fixed intermediate cooling field

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