Qualitative insight and quantitative analysis of the effect of temperature on the coercivity of a magnetic system

Moskalenko, M. A.; Bessarab, Pavel F.; Uzdin, V. M.; Jónsson, Hannes

doi:10.1063/1.4942428

Cited by 10 publications

(8 citation statements)

References 54 publications

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“…We note that the methodology used here for calculating pre-exponential factors in the Arrhenius rate expressions for magnetic transitions, HTST, has been shown to give results in good agreement with experimentally measured prefactors for remagnetization of Fe islands on a W(110) surface [23] and simulations of hysteresis loops of spring magnets [24]. Also, the calculated activation energy for annihilation of a magnetic skyrmion obtained with this methodology is in close agreement with direct Landau-Lifshitz-Gilbert simulations carried out at a relatively high temperature (where the life time is short enough for such direct simulations) [25].…”

Section: Discussionsupporting

confidence: 69%

The effect of temperature and external field on transitions in elements of kagome spin ice

2017

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Transitions between magnetic states of one and two ring kagome spin ice elements consisting of 6 and 11 prolate magnetic islands are calculated and the lifetime of the ground states evaluated using harmonic transition state theory and the stationary state approximation. The calculated values are in close agreement with experimental lifetime measurements made by Farhan and co-workers (Farhan et al 2013 Nat. Phys. 9 375) when values of the parameters in the Hamiltonian are chosen to be best estimates for a single island, obtained from measurements and micromagnetic modeling. The effective pre-exponential factor in the Arrhenius rate law for the elementary steps turns out to be quite small, on the order of 10 9 s −1 , three orders of magnitude smaller than has been assumed in previous analysis of the experimental data, while the effective activation energy is correspondingly lower than the previous estimate. The application of an external magnetic field is found to strongly affect the energy landscape of the system. Even a field of 4 mT can eliminate states that correspond to ground states in the absence of a field. The theoretical approach presented here and the close agreement found with experimental data demonstrates that the properties of spin ice systems can be calculated using the tools of rate theory and a Hamiltonian parametrized only from the properties of a single island.

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Section: Discussionsupporting

confidence: 69%

The effect of temperature and external field on transitions in elements of kagome spin ice

2017

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“…1,2 Thermal activation also needs to be taken into account when assessing the stability of a system with respect to external perturbations such as a magnetic eld, contributing, for example, to the temperature dependence of hysteresis loops. 3 Thermal stability is a particularly important issue in the context of novel information storage devices. As the size of such devices is reduced, the thermal stability of the magnetic states decreases.…”

Section: Introductionmentioning

confidence: 99%

Classical to quantum mechanical tunneling mechanism crossover in thermal transitions between magnetic states

et al. 2016

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Transitions between states of a magnetic system can occur by jumps over an energy barrier or by quantum mechanical tunneling through the energy barrier. The rate of such transitions is an important consideration when the stability of magnetic states is assessed for example for nanoscale candidates for data storage devices. The shift in transition mechanism from jumps to tunneling as the temperature is lowered is analyzed and a general expression derived for the crossover temperature. The jump rate is evaluated using a harmonic approximation to transition state theory. First, the minimum energy path for the transition is found with the geodesic nudged elastic band method. The activation energy for the jumps is obtained from the maximum along the path, a saddle point on the energy surface, and the eigenvalues of the Hessian matrix at that point as well as at the initial state minimum used to estimate the entropic pre-exponential factor. The crossover temperature for quantum mechanical tunneling is evaluated from the second derivatives of the energy with respect to orientation of the spin vector at the saddle point. The resulting expression is applied to test problems where analytical results have previously been derived, namely uniaxial and biaxial spin systems with two-fold anisotropy. The effect of adding four-fold anisotropy on the crossover temperature is demonstrated. Calculations of the jump rate and crossover temperature for tunneling are also made for a molecular magnet containing an Mn group. The results are in excellent agreement with previously reported experimental measurements on this system.

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“…This expression can be used to estimate the magnetic field needed to reverse the magnetization at a given temperature and for a given timescale. A similar model has been used to analyze the reversal of magnetization in a spring magnet [18]. In typical experimental measurements, including those of de Vries et al, the magnetic field is increased at a constant rate, R = ∆H/∆t until the magnetization reverses.…”

Section: Modelmentioning

confidence: 99%

Calculations of switching field and energy barrier for magnetic islands with perpendicular anisotropy

Liashko¹,

Jónsson²,

Uzdin³

2017

Nanosystems: Phys. Chem. Math.

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Calculations of the magnetic field required to reverse the magnetization of islands with out-of-plane anisotropy are carried out using a model describing nucleation followed by rapid domain wall motion. The calculations are based on an extension of the Stoner-Wohlfarth model where thermal activation is taken into account as well as the applied magnetic field. The calculated switching field distribution (SFD) is compared with recently reported experimental measurements of de Vries et al. [New J. Phys. 19, 093019 (2017)] on circular 220 nm CoPt islands.The measured results can be closely reproduced by choosing appropriate values of two parameters, the nucleation volume, and the effective anisotropy. Both the position of SDF peaks and their width at high and low temperature, 300 K and 10 K, are amply described using the same set of parameter values for a given island, while there is a large difference between islands with weak and strong magnetic anisotropies. There is no need to introduce the temperature dependence of the activation energy at zero field. This is in contrast with the estimates obtained from the so-called diamond model used by de Vries et al. in their data analysis where multiple adjustable parameters are introduced, and a three-to fourfold change in the zero field activation energy is invoked.

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Qualitative insight and quantitative analysis of the effect of temperature on the coercivity of a magnetic system

Cited by 10 publications

References 54 publications

The effect of temperature and external field on transitions in elements of kagome spin ice

The effect of temperature and external field on transitions in elements of kagome spin ice

Classical to quantum mechanical tunneling mechanism crossover in thermal transitions between magnetic states

Calculations of switching field and energy barrier for magnetic islands with perpendicular anisotropy

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