Mechanism of magnetic heating in Mn-doped magnetite nanoparticles and the role of intertwined structural and magnetic properties

Bianco, L. Del; Spizzo, F.; Barucca, G.; Ruggiero, María; Crich, Simonetta Geninatti; Forzan, Michele; Sieni, Elisabetta; Sgarbossa, Paolo

doi:10.1039/c9nr03131f

Cited by 28 publications

(34 citation statements)

References 65 publications

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“…Actually, in the investigated samples the nanoparticles are not isolated, but they form large aggregates and even exhibit a tendency to coalesce, as observed in Figure 1. Therefore, the high values of T irr are consistent with the existence of magnetic interactions among the nanoparticles, resulting in an increase of their anisotropy energy barriers for magnetization reversal and shifting to higher temperature or preventing their entrance in the superparamagnetic regime [91,93,94]. In other words, one can consider that the nanoparticles are subjected to an effective magnetic anisotropy K eff higher than the anisotropy that operates when they are isolated.…”

Section: Squidmentioning

confidence: 65%

“…The values of T irr are much higher than expected for non-interacting maghemite nanoparticles as small as the ones we are considering. In fact, assuming the Néel expression for the relaxation time of the magnetic moment of a nanoparticle [91] and in the adopted experimental conditions (in SQUID magnetometry, the measuring time is assumed equal to 100 s), the blocking temperature T B can be estimated using the relation T B = KV/25k B , where K= 5 × 10 4 erg/cm 3 [87] is the magnetocrystalline anisotropy of bulk maghemite and V is the particle volume [92,93]. For a nanoparticle of the sample Iolitec,~11 nm in size, T B~1 0 K is calculated and obviously lower values would be obtained for the P520 and P200 nanoparticles.…”

Section: Squidmentioning

confidence: 99%

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Local Structure and Magnetism of Fe2O3 Maghemite Nanocrystals: The Role of Crystal Dimension

et al. 2020

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Here we report on the impact of reducing the crystalline size on the structural and magnetic properties of γ-Fe2O3 maghemite nanoparticles. A set of polycrystalline specimens with crystallite size ranging from ~2 to ~50 nm was obtained combining microwave plasma synthesis and commercial samples. Crystallite size was derived by electron microscopy and synchrotron powder diffraction, which was used also to investigate the crystallographic structure. The local atomic structure was inquired combining pair distribution function (PDF) and X-ray absorption spectroscopy (XAS). PDF revealed that reducing the crystal dimension induces the depletion of the amount of Fe tetrahedral sites. XAS confirmed significant bond distance expansion and a loose Fe-Fe connectivity between octahedral and tetrahedral sites. Molecular dynamics revealed important surface effects, whose implementation in PDF reproduces the first shells of experimental curves. The structural disorder affects the magnetic properties more and more with decreasing the nanoparticle size. In particular, the saturation magnetization reduces, revealing a spin canting effect. Moreover, a large effective magnetic anisotropy is measured at low temperature together with an exchange bias effect, a behavior that we related to the existence of a highly disordered glassy magnetic phase.

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Section: Squidmentioning

confidence: 65%

Section: Squidmentioning

confidence: 99%

Local Structure and Magnetism of Fe2O3 Maghemite Nanocrystals: The Role of Crystal Dimension

et al. 2020

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“…In Table 1, we report the values of coercivity H C and of the irreversibility field H irr . The latter parameter is the field at which the ascending and descending branches of the hysteresis loop join together, and it may be considered a measure of the anisotropy field of the system, i.e., H irr = 2 K eff /M S , where K eff is the effective anisotropy [56,57]. In order to calculate K eff from this relationship, M S must be expressed in (emu/cm 3 ); namely, the value of M S for MNP must be multiplied by the density of the Fe oxide phase, which we conventionally take to be 5 g/cm 3 , corresponding to the average of bulk Fe 3 O 4 and γ-Fe 2 O 3 .…”

Section: Resultsmentioning

confidence: 99%

Glassy Magnetic Behavior and Correlation Length in Nanogranular Fe-Oxide and Au/Fe-Oxide Samples

et al. 2019

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In nanoscale magnetic systems, the possible coexistence of structural disorder and competing magnetic interactions may determine the appearance of a glassy magnetic behavior, implying the onset of a low-temperature disordered collective state of frozen magnetic moments. This phenomenology is the object of an intense research activity, stimulated by a fundamental scientific interest and by the need to clarify how disordered magnetism effects may affect the performance of magnetic devices (e.g., sensors and data storage media). We report the results of a magnetic study that aims to broaden the basic knowledge of glassy magnetic systems and concerns the comparison between two samples, prepared by a polyol method. The first can be described as a nanogranular spinel Fe-oxide phase composed of ultrafine nanocrystallites (size of the order of 1 nm); in the second, the Fe-oxide phase incorporated non-magnetic Au nanoparticles (10–20 nm in size). In both samples, the Fe-oxide phase exhibits a glassy magnetic behavior and the nanocrystallite moments undergo a very similar freezing process. However, in the frozen regime, the Au/Fe-oxide composite sample is magnetically softer. This effect is explained by considering that the Au nanoparticles constitute physical constraints that limit the length of magnetic correlation between the frozen Fe-oxide moments.

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“…As formerly indicated by Dormann et al [ 39 ], dipolar magnetic interactions lead to an increase of the anisotropy energy barriers of the NPs. In the case of small and soft NPs, this effect improves the thermal stability of their magnetic moments, shifting to higher temperature or preventing the entrance in the superparamagnetic regime [ 39 , 129 , 149 , 173 , 174 , 175 , 176 ]. Under the conditions of validity of the LRT (i.e., in the linear regime), dipolar interactions can vary the Néel relaxation time τ N so as to approach the resonant condition f m τ N = 1 or move away from it, which leads to an increase or decrease of the hysteresis loop area, respectively; in the nonlinear regime, increasing τ N so as to pass from the superparamagnetic state (f m τ N < 1) to the blocked one (f m τ N > 1) increases more and more the hysteresis loop area, at least until demagnetizing effects become prevalent [ 172 ].…”

Section: Multicore Nanoparticles (Mc_nps)mentioning

confidence: 99%

Nanoparticles for Magnetic Heating: When Two (or More) Is Better Than One

et al. 2021

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The increasing use of magnetic nanoparticles as heating agents in biomedicine is driven by their proven utility in hyperthermia therapeutic treatments and heat-triggered drug delivery methods. The growing demand of efficient and versatile nanoheaters has prompted the creation of novel types of magnetic nanoparticle systems exploiting the magnetic interaction (exchange or dipolar in nature) between two or more constituent magnetic elements (magnetic phases, primary nanoparticles) to enhance and tune the heating power. This process occurred in parallel with the progress in the methods for the chemical synthesis of nanostructures and in the comprehension of magnetic phenomena at the nanoscale. Therefore, complex magnetic architectures have been realized that we classify as: (a) core/shell nanoparticles; (b) multicore nanoparticles; (c) linear aggregates; (d) hybrid systems; (e) mixed nanoparticle systems. After a general introduction to the magnetic heating phenomenology, we illustrate the different classes of nanoparticle systems and the strategic novelty they represent. We review some of the research works that have significantly contributed to clarify the relationship between the compositional and structural properties, as determined by the synthetic process, the magnetic properties and the heating mechanism.

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Mechanism of magnetic heating in Mn-doped magnetite nanoparticles and the role of intertwined structural and magnetic properties

Abstract: The heating efficiency of an assembly of Mn-doped magnetite nanoparticles can be tuned so as to depend linearly on the non-superparamagnetic fraction.

Cited by 28 publications

References 65 publications

Local Structure and Magnetism of Fe2O3 Maghemite Nanocrystals: The Role of Crystal Dimension

Local Structure and Magnetism of Fe2O3 Maghemite Nanocrystals: The Role of Crystal Dimension

Glassy Magnetic Behavior and Correlation Length in Nanogranular Fe-Oxide and Au/Fe-Oxide Samples

Nanoparticles for Magnetic Heating: When Two (or More) Is Better Than One

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