Hysteresis multicycles in nanomagnet arrays

Mai, Trieu; Narayan, Onuttom

doi:10.1103/physreve.71.026120

Cited by 15 publications

(12 citation statements)

References 22 publications

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“…There is another fundamental explanation for the observed RPM-CPM asymmetry [26]. Even when the Hamiltonian is constructed to possess spin-inversion symmetry, the dynamics describing how the magnetization changes do not have to be.…”

Section: B Model 2: the Raim Plus Llg Dynamicsmentioning

confidence: 99%

Disorder-induced magnetic memory: Experiments and theories

et al. 2007

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Beautiful theories of magnetic hysteresis based on random microscopic disorder have been developed over the past ten years. Our goal was to directly compare these theories with precise experiments. We first developed and then applied coherent x-ray speckle metrology to a series of thin multilayer perpendicular magnetic materials. To directly observe the effects of disorder, we deliberately introduced increasing degrees of disorder into our films. We used coherent x-rays to generate highly speckled magnetic scattering patterns. The apparently random arrangement of the speckles is due to the exact configuration of the magnetic domains in the sample. In effect, each speckle pattern acts as a unique fingerprint for the magnetic domain configuration. Small changes in the domain structure change the speckles, and comparison of the different speckle patterns provides a quantitative determination of how much the domain structure has changed. How is the magnetic domain configuration at one point on the major hysteresis loop related to the configurations at the same point on the loop during subsequent cycles? The microscopic return-point memory(RPM) is partial and imperfect in the disordered samples, and completely absent when the disorder was not present. We found the complementary-point memory(CPM) is also partial and imperfect in the disordered samples and completely absent when the disorder was not present. We found that the RPM is always a little larger than the CPM. We also studied the correlations between the domains within a single ascending or descending loop. We developed new theoretical models that do fit our experiments.Comment: 26 pages, 25 figures, Accepted by Physical Review B 01/25/0

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Section: B Model 2: the Raim Plus Llg Dynamicsmentioning

confidence: 99%

Disorder-induced magnetic memory: Experiments and theories

et al. 2007

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“…Even if the energy is spininversion-symmetric, the dynamics governing the spin reversal are not required to be. Our simulations of a spinreversal-symmetric, disordered vector-spin model with strong Ising-like (locally varying) anisotropy, with the dynamics given by the standard Landau-Lifshitz-GilbertBloch-Bloembergen formalism, show dynamic symmetry breaking [8]. Note that then the time evolution of any spin is given by a precessional term, which is unchanged under spin (and field) reversal, and by a relaxational term, which is reversed.…”

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confidence: 95%

Disorder-Induced Microscopic Magnetic Memory

et al. 2005

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Using coherent x-ray speckle metrology, we have measured the influence of disorder on major loop return point memory (RPM) and complementary point memory (CPM) for a series of perpendicular anisotropy Co/Pt multilayer films. In the low disorder limit, the domain structures show no memory with field cycling--no RPM and no CPM. With increasing disorder, we observe the onset and the saturation of both the RPM and the CPM. These results provide the first direct ensemble-sensitive experimental study of the effects of varying disorder on microscopic magnetic memory and are compared against the predictions of existing theories.

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“…The need of smaller memory storage devices, [1,2,3,4,5,6,7,8,9,10,11,12,13,14] the interest in developing quantum computing, [15] and the hope for understanding the relationship between the macroscopic and microscopic magnetic behaviors has led intense research into the properties of nanoscale magnets. [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32] Many issues still remain unclear and serious problems must be overcome in order for them to be technologically useful.…”

Section: Introductionmentioning

confidence: 99%

“…[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32] Many issues still remain unclear and serious problems must be overcome in order for them to be technologically useful. Prominent among these is the loss of memory during magnetic relaxation.…”

Section: Introductionmentioning

confidence: 99%

“…[8] Moreover, since interdot exchange interactions are negligibly small, the dynamics of the ferromagnetic nanodot arrangements are strongly influenced by dipolar interdot interactions. [13,14] Single molecule magnets (SMM's) consist of clusters of only a few magnetic ions, and are thus among the smallest and simplest nanomagnets, but are also wellcharacterized systems exhibiting magnetic hysteresis. [27] In SMM's, the one-body tunnel picture of the magnetization mostly explains this phenomenon in the sense that the sequence of discrete steps in those curves provides evidence for resonant coherent quantum tunneling.…”

Section: Introductionmentioning

confidence: 99%

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Effect of dipolar interactions on the magnetization of a cubic array of nanomagnets

2005

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We investigated the effect of intermolecular dipolar interactions on an ensemble of 100 3D-systems of 5×5×4 nanomagnets, each with spin S = 5, arranged in a cubic lattice. We employed the LandauLifshitz-Gilbert equation to solve for the magnetization curves for several values of the damping constant, the induction sweep rate, the lattice constant, the temperature, and the magnetic anisotropy. We find that the smaller the damping constant, the stronger the maximum induction required to produce hysteresis. The shape of the hysteresis loops also depends on the damping constant. We find further that the system magnetizes and demagnetizes at decreasing magnetic field strengths with decreasing sweep rates, resulting in smaller hysteresis loops. Variations of the lattice constant within realistic values (1.5 nm -2.5 nm) show that the dipolar interaction plays an important role in the magnetic hysteresis by controlling the relaxation process. The temperature dependencies of the damping constant and of the magnetization are presented and discussed with regard to recent experimental data on nanomagnets. Magnetic anisotropy enhances the size of the hysteresis loops for external fields parallel to the anisotropy axis, but decreases it for perpendicular external fields. Finally, we reproduce and test a previously reported magnetization curve for a 2D-system [M. Kayali and W. Saslow, Phys. Rev. B 70, 174404 (2004)]. We show that its hysteretic behavior is only weakly dependent on the shape anisotropy field and the sweep rate, but depends sensitively upon the dipolar interactions. Although in 3D systems, dipole-dipole interactions generally diminish the hysteresis, in two-dimensional systems, they strongly enhance it. For both square two-dimensional and rectangular three-dimensional lattices with B||(x+ŷ), dipole-dipole interactions can cause large jumps in the magnetization.

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Hysteresis multicycles in nanomagnet arrays

Cited by 15 publications

References 22 publications

Disorder-induced magnetic memory: Experiments and theories

Disorder-induced magnetic memory: Experiments and theories

Disorder-Induced Microscopic Magnetic Memory

Effect of dipolar interactions on the magnetization of a cubic array of nanomagnets

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