Determination of the blocking temperature of magnetic nanoparticles: The good, the bad, and the ugly

Bruvera, I. J.; Zélis, P. Mendoza; Calatayud, M. Pilar; Goya, Gerardo F.; Sánchez, F.

doi:10.1063/1.4935484

Cited by 220 publications

(147 citation statements)

References 26 publications

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“…The field‐cooled (FC, purple) and zero‐field‐cooled (ZFC, gray) magnetization curves show that these Fe 3 O 4 nanoparticles are superparamagnetic (Figure b). A d(ZFC‐FC)/d T analysis shows the distribution of the blocking temperature ( T B ) and reveals a mean value of 〈 T B 〉 = 13.5 K (Figure c) . Upon continuous white‐light irradiation from a tungsten‐halogen lamp (color temperature of 3250 K and a power of ≈3 mW), the saturation magnetization of these 7.0 nm Fe 3 O 4 nanoparticles decreased by ≈1.2% when held in the “blocked” state at 5.0 K (Figure d).…”

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Persistent Photomagnetism in Superparamagnetic Iron Oxide Nanoparticles

DuChene

Puretzky

et al. 2018

Adv Elect Materials

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phenomenon. [12][13][14][15] However, no experimental evidence was provided to exclude the light-induced photothermal effect and incontrovertibly demonstrate the existence of light-induced spin transitions in these metal-oxide systems. More importantly, it is noted that the photogenerated electrons in transition metal oxides are free to roam within the solid, [16,17] preventing them from directly altering the metal centers' spin configuration via localization on a single atomic site. This fundamental difference between material systems casts doubt over the validity of adopting the steady-state spin transition theory to describe photomagnetism in nanoparticlebased magnets.In this contribution, we examined the magnetic response of superparamagnetic Fe 3 O 4 nanoparticles following photoexcitation and found that the exciton-spin exchange-coupling interaction is the primary mechanism by which this archetypal transition metal oxide exhibits photomagnetism. Studying the photomagnetic response at temperatures below the blocking temperature under various external fields revealed that the exciton-spin exchange-coupling interaction reduces the magnetic energy barrier governing spin-flip transitions within iron oxide nanoparticles, allowing an optically driven magnetic phase transition from ferrimagnetic to superparamagnetic when held in their "blocked" state and a corresponding decrease in their saturation magnetization. Further investigation showed a significant decrease in photomagnetism as the Fe 3 O 4 nanoparticle size was increased, pinpointing the critical role of restricting the nanoparticle's magnetic anisotropy in enabling photomagnetism. Significantly, we have excluded light-induced photothermal heating as the source of photomagnetism in Fe 3 O 4 nanoparticles by comparing experimentally measured magnetization changes with those predicted from theoretical simulations based on a photothermal mechanism. Taken together, our findings provide fundamental insights into the origin of photomagnetism in transition metal oxides and establish a deeper understanding of the underlying mechanism that regulates the light-induced spin dynamics in iron oxide nanoparticles.High-resolution transmission electron microscopy (HRTEM) reveals that spherical nanoparticles were produced with an average size of 7.0 ± 1.0 nm (Figure 1a, also see Figure S1a,b in the Supporting Information). X-ray photoelectron spectroscopy Using light irradiation to manipulate magnetization over a prolonged period of time offers a wealth of opportunities for spin-based electronics and photonics. To date, persistent photomagnetism has been frequently reported in spin systems composed of molecular magnets; yet this phenomenon is rarely observed in nanoparticle-based systems comprised of transition metal oxides. Here, detailed studies of persistent photomagnetism in superparamagnetic iron oxide (Fe 3 O 4 ) nanoparticles at temperatures below their blocking temperature are presented and it is demonstrated that the magnetization change does not occur through stea...

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confidence: 99%

Persistent Photomagnetism in Superparamagnetic Iron Oxide Nanoparticles

DuChene

Puretzky

et al. 2018

Adv Elect Materials

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“…Although ZFC/FC curves are easily measured, how to precisely determine phase‐transition‐like temperature between superparamagnetic and blocked states is controversial due to a finite width of transition temperature range . It is well‐known that the ZFC curve is given by net magnetization projection along field of randomly frozen magnetic moments and of polarized superparamagnetic ones.…”

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Spin‐Glass Irreversibility Temperature and Magnetic Stabilization in Ferromagnet/Spin‐Glass Bilayers

2019

Physica Rapid Research Ltrs

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The authors numerically studied the irreversibility temperature (Tirr) of a spin glass (SG) and how to use a SG to stabilize a ferromagnet. The rate of Tirr/SG‐anisotropic‐field increment can reach ≈121 K T−1. In ferromagnet/SG bilayers, exchange bias (EB) may be enhanced fivefold at 10 K with increasing interfacial coupling (JIF), whereas the EB blocking temperature (TBEB) does not change. However, decreases in SG exchange coupling (JSG) can twofold enhance TBEB with maintaining a table‐like EB. On the contrary, small JIF and large JSG are both destructive to coercivity. Nevertheless, EB field and coercivity are switchable, opening an opportunity to design temperature‐controlled write‐to‐read switches.

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“…Thus, in order to properly determine and compare T B values of the samples, it is helpful to calculate the mean blocking temperatures < T B >. Additionally, the distribution of the energy barriers has been obtained by a direct subtraction of the field cooled and zero field cooled branches of magnetization versus temperature measurements through the derivative − d ( χ FC - χ ZFC )/ dT curves [36,37] (Supplementary Information, Model S1). This difference is proportional to the number of particles in the blocked regime that decreases when the thermal energy overcomes the anisotropy energy of each nanoparticle at increasing temperatures.…”

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confidence: 99%

Exploring Reaction Conditions to Improve the Magnetic Response of Cobalt-Doped Ferrite Nanoparticles

et al. 2018

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With the aim of studying the influence of synthesis parameters in structural and magnetic properties of cobalt-doped magnetite nanoparticles, Fe3−xCoxO4 (0 < x < 0.15) samples were synthetized by thermal decomposition method at different reaction times (30–120 min). The Co ferrite nanoparticles are monodisperse with diameters between 6 and 11 nm and morphologies depending on reaction times, varying from spheric, cuboctahedral, to cubic. Chemical analysis and X-ray diffraction were used to confirm the composition, high crystallinity, and pure-phase structure. The investigation of the magnetic properties, both magnetization and electronic magnetic resonance, has led the conditions to improve the magnetic response of doped nanoparticles. Magnetization values of 86 emu·g−1 at room temperature (R.T.) have been obtained for the sample with the highest Co content and the highest reflux time. Magnetic characterization also displays a dependence of the magnetic anisotropy constant with the varying cobalt content.

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Determination of the blocking temperature of magnetic nanoparticles: The good, the bad, and the ugly

Cited by 220 publications

References 26 publications

Persistent Photomagnetism in Superparamagnetic Iron Oxide Nanoparticles

Persistent Photomagnetism in Superparamagnetic Iron Oxide Nanoparticles

Spin‐Glass Irreversibility Temperature and Magnetic Stabilization in Ferromagnet/Spin‐Glass Bilayers

Exploring Reaction Conditions to Improve the Magnetic Response of Cobalt-Doped Ferrite Nanoparticles

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