Probing magnetization dynamics in individual magnetite nanocrystals using magnetoresistive scanning tunneling microscopy

Hevroni, Amir; Tsukerman, Boris; Markovich, Gil

doi:10.1103/physrevb.92.224423

Cited by 7 publications

(10 citation statements)

References 34 publications

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“…All of the data for a given chain type overlap, in agreement with Eq. (34). The figure also shows that as the relative distance between the particles decreases, thereby enhancing the dipolar interaction strength, the produced heat increases for Z chains and decreases for X chains.…”

Section: Resultsmentioning

confidence: 82%

“…It is worth pointing out that the thermally activated dynamics of MPs considered here, sometimes termed as the Néel-Brown theory or the discrete orientation model [24], is in the limit of high energy barriers and high damping fully consistent with the Langevin dynamics approach based on the stochastic Landau-Lifshitz-Gilbert equation [24,30,31]. The present master-equation approach has been subject to successful experimental validations [32][33][34], and is the method of choice for studying the long-time-scale thermally activated dynamics when the Langevin framework becomes computationally inefficient.…”

Section: Model Of Thermally Activated Particle Chainsmentioning

confidence: 67%

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Thermodynamics of interacting magnetic nanoparticles

et al. 2020

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We apply the concepts of stochastic thermodynamics combined with the transition state theory to develop a framework for evaluating local heat distributions across the assemblies of interacting magnetic nanoparticles (MP) subject to time-varying external magnetic fields. We show that additivity of entropy production in the particle state-space allows separating the entropy contributions and evaluating the heat produced by the individual MPs despite interactions. Using MP chains as a model system for convenience, without losing generality, we show that the presence of dipolar interactions leads to significant heat distributions across the chains. Our study also suggests that the typically used hysteresis loops cannot be used as a measure of energy dissipation at the local particle level within MP clusters, aggregates or assemblies, and explicit evaluation of entropy production based on appropriate theory, such as developed here, becomes necessary.

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Section: Resultsmentioning

confidence: 82%

Section: Model Of Thermally Activated Particle Chainsmentioning

confidence: 67%

Thermodynamics of interacting magnetic nanoparticles

et al. 2020

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“…Alternatively, the temperature can be varied to destabilize a small magnetic particle. Hevroni et al have recently investigated the temperature dependence of TMR fluctuations in magnetite nanoparticles on a Co film using scanning tunneling microscopy 49 . In our study, all experiments were done at room temperature.…”

Section: Random Telegraph Noise and Anisotropymentioning

confidence: 99%

Size and voltage dependence of effective anisotropy in sub-100-nm perpendicular magnetic tunnel junctions

et al. 2016

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Magnetic tunnel junctions with perpendicular magnetic anisotropy are investigated using a conductive atomic force microscope. The 1.23 nm Co 40 Fe 40 B 20 recording layer coercivity exhibits a size dependence which suggests single domain behavior for diameters ≤ 100 nm. Focusing on devices with diameters smaller than 100 nm, we determine the effect of voltage and size on the effective device anisotropy K eff using two different techniques. K eff is extracted both from distributions of the switching fields of the recording and reference layers, and from measurement of thermal fluctuations of the recording layer magnetization when a field close to the switching field is applied. The results from both sets of measurements reveal that K eff increases monotonically with decreasing junction diameter, consistent with the size dependence of the demagnetization energy density. We demonstrate that K eff can be controlled with a voltage down to the smallest size measured, 64 nm. PACS numbers: 85.75.-d,73.40.Gk,75.78.-n,75.70.-i 1 I. INTRODUCTION Magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) are an attractive building block for non-volatile memories. PMA MTJs (p-MTJs) show promisein terms of the key requirements for implementation into products competitive with current data storage and memory technologies: large tunnel magnetoresistance (TMR), low writing energy cost, non-volatility over ∼ 10 years, and scalability of these properties toward ∼ 1 Tbit/inch 2 densities. Room temperature TMR ratios greater than 100% have long existed in in-plane MTJs 1,2 . In state of the art in-plane MTJs, TMR in excess of 600% is achieved by controlling the diffusion of Ta in the film stack through the addition of boron to the magnetic electrodes 3 . Despite these achievements, in-plane MTJs suffer from scalability issues due to their dependence on shape anisotropy for thermal stability and the high energy cost of switching the magnetization by the spin transfer torque (STT) effect 4,5 . For in-plane MTJs, switching energies E sw = I 2 c Rt, where I c is the critical switching current, R is the resistance, and t is the length of the pulse, of approximately 10 µJ/bit were achieved for current pulses on the order of 10 ms 6 . This value was drastically reduced using nanosecond pulses, yielding E sw on the order of single pJ/bit in purely in-plane MTJs 7 . In high TMR p-MTJs the large out-of-plane demagnetization energy does not contribute to E sw 8 . Recently, TMR ratios up to 162% were obtained in p-MTJs by further controlling interlayer diffusion through the substitution of Ta with Mo in the film stack 9 . PMA is achieved when the CoFeB thickness is less than about 1.5 nm, so that the effective anisotropy K eff is dominated by the interfacial anisotropy between Fe in the CoFeB and oxygen in the MgO 10 . In such p-MTJs, switching energies of hundreds of fJ/bit were achieved in 60 nm × 170 nm ellipses 11 . One of the most promising aspects of p-MTJs is that the interface anisotropy can be controlled by applying a...

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“…The frequency of this fluctuation at physiological temperature is significant and measured to be in the GHz frequency range through low-frequency magnetic susceptibility, Mossbauer spectroscopy, and neutron spin-echo spectroscopy (Kilcoyne and Cywinski, 1995; Allen et al, 2000; Casalta et al, 1999). Such superparamagnetic moment fluctuations have also been experimentally observed on a single particle scale at low temperatures (Wernsdorfer et al, 1997; Piotrowski et al, 2014; Hevroni et al, 2015). Therefore, the ion channel in the vicinity of the potentially superparamagnetic iron-loaded ferritin experiences large magnetic field gradients and Tesla-scale magnetic fields at GHz frequencies, as well as the corresponding GHz frequency diamagnetic forces and torques, as discussed earlier.…”

Section: Resultsmentioning

confidence: 81%

Possible magneto-mechanical and magneto-thermal mechanisms of ion channel activation in magnetogenetics

Barbic

2019

eLife

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The palette of tools for perturbation of neural activity is continually expanding. On the forefront of this expansion is magnetogenetics, where ion channels are genetically engineered to be closely coupled to the iron-storage protein ferritin. Initial reports on magnetogenetics have sparked a vigorous debate on the plausibility of physical mechanisms of ion channel activation by means of external magnetic fields. The criticism leveled against magnetogenetics as being physically implausible is based on the specific assumptions about the magnetic spin configurations of iron in ferritin. I consider here a wider range of possible spin configurations of iron in ferritin and the consequences these might have in magnetogenetics. I propose several new magneto-mechanical and magneto-thermal mechanisms of ion channel activation that may clarify some of the mysteries that presently challenge our understanding of the reported biological experiments. Finally, I present some additional puzzles that will require further theoretical and experimental investigation.

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Probing magnetization dynamics in individual magnetite nanocrystals using magnetoresistive scanning tunneling microscopy

Cited by 7 publications

References 34 publications

Thermodynamics of interacting magnetic nanoparticles

Thermodynamics of interacting magnetic nanoparticles

Size and voltage dependence of effective anisotropy in sub-100-nm perpendicular magnetic tunnel junctions

Possible magneto-mechanical and magneto-thermal mechanisms of ion channel activation in magnetogenetics

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