scholarly journals Magnetization Reversal in Ferromagnetic Nanorings of Fourfold Symmetries

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Andrea Ehrmann ◽  
Tomasz Blachowicz
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetization Reversal ◽  
Domain Walls ◽  
Memory Devices ◽  
Micromagnetic Simulations ◽  
Stable Intermediate ◽  
Intermediate States ◽  
The Stability ◽  
Ferromagnetic Nanorings

Magnetic nanoparticles offer a broad spectrum of magnetization reversal processes and respective magnetic states, such as onion, horseshoe, or vortex states as well as various states including domain walls. These states can be correlated with stable intermediate states at remanence, enabling new quaternary memory devices storing two bits in one particle. The stability of these intermediated states was tested with respect to shape modifications, variations in the anisotropy axes, and rotations and fluctuations of the external magnetic field. In our micromagnetic simulations, 6 different stable intermediate states were observed at vanishing magnetic field in addition to the remanence state. The angular region of approx. 5°–12° between nanoring and external magnetic field was identified as being most stable with respect to all modifications, with an onion state as technologically best accessible intermediate state to create quaternary memory devices.

scholarly journals Magnetization Reversal in Concave Iron Nano-Superellipses

2021 ◽  
Vol 6 (2) ◽  
pp. 17
Author(s):  
Emre Öncü ◽  
Andrea Ehrmann
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetization Reversal ◽  
Hysteresis Loops ◽  
Strong Impact ◽  
Research Groups ◽  
Micromagnetic Simulations ◽  
Magnetic Nanodots ◽  
Reversal Process ◽  
Magnetization Reversal Process

Square magnetic nanodots can show intentional or undesired shape modifications, resulting in superellipses with concave or convex edges. Some research groups also concentrated on experimentally investigating or simulating concave nano-superellipses, sometimes called magnetic astroids due to their similarity to the mathematical shape of an astroid. Due to the strong impact of shape anisotropy in nanostructures, the magnetization-reversal process including coercive and reversibility fields can be expected to be different in concave or convex superellipses than that in common squares. Here, we present angle-dependent micromagnetic simulations on magnetic nanodots with the shape of concave superellipses. While magnetization reversal occurs via meander states, horseshoe states or the 180° rotation of magnetization for the perfect square, depending on the angle of the external magnetic field, more complicated states occur for superellipses with strong concaveness. Even apparently asymmetric hysteresis loops can be found along the hard magnetization directions, which can be attributed to measuring minor loops since the reversibility fields become much larger than the coercive fields.

Micromagnetic Simulation of CoFe Magnetic Nanorings: Switching Behavior in External Magnetic Field

2013 ◽  
Vol 710 ◽  
pp. 80-84 ◽  
Author(s):  
Zhen Gang Guo ◽  
Li Qing Pan ◽  
Hong Mei Qiu ◽  
M. Yasir Rafique ◽  
Shuai Zeng
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Magnetization Reversal ◽  
Domain Walls ◽  
Vortex State ◽  
Switching Behavior ◽  
Switching Field ◽  
Reversal Process ◽  
Magnetic States ◽  
Magnetization Processes

The magnetization reversal processes of magnetic nanorings (Co50Fe50) with different geometric shapes are investigated. In addition to the expected onion and vortex magnetization states, other metastable states are observed in the magnetization processes. We anatomize the formation and transition of magnetic states, and the propagation and annihilation of domain walls in the reversal process through the dynamic picture. Phase diagrams for the magnetization switching behavior depending on the geometric parameters are presented. The simulation shows that the vortex state is stabilized in thick and narrow rings. The switching field from vortex to onion states turns out to increase with thickness and decrease with width and diameter.

Convective instability of a plasma slab in a magnetic field

1980 ◽  
Vol 24 (3) ◽  
pp. 479-482 ◽  
Author(s):  
K. Bhimsen ◽  
Shivamoggi ◽  
Mahinder ◽  
S. Uberoi
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Convective Instability ◽  
Ionization Rate ◽  
Plasma Slab ◽  
The Stability

Convective instability of a plasma slab (contained between two metal walls) subject to a longitudinal external magnetic field is studied. The results show that (i) increase in the ionization rate Z causes a reduction in the stability of the plasma; (ii) the instability persists in the limit k ⇒ 0.

Effect of External Magnetic Field Loaded at the Initial Period of Inertial Stretching Stage on the Stability of Shaped Charge Jet

2017 ◽  
Vol 45 (5) ◽  
pp. 875-881 ◽  
Author(s):  
Bin Ma ◽  
Zhengxiang Huang ◽  
Qiangqiang Xiao ◽  
Xudong Zu ◽  
Xin Jia ◽  
...  
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Initial Period ◽  
Shaped Charge ◽  
The Stability ◽  
Shaped Charge Jet

Effects of Magnetic Domain Walls on the Anisotropic Magnetoresistance in NiFe Nanowires

2015 ◽  
Vol 15 (10) ◽  
pp. 7620-7623 ◽  
Author(s):  
Chunghee Nam
Keyword(s):  
Magnetic Field ◽  
Magnetic Force ◽  
Domain Walls ◽  
Magnetic Domain ◽  
Anisotropic Magnetoresistance ◽  
Magnetic Force Microscope ◽  
Micromagnetic Simulations ◽  
Magnetic Domain Walls ◽  
Magnetic Wires ◽  
Low Magnetic Field

We show that a type of magnetic domain walls (DWs) can be monitored by anisotropic magnetoresistance (AMR) measurements due to a specific DW volume depending on the DW type in NiFe magnetic wires. A circular DW injection pad is used to generate DWs at a low magnetic field, resulting in reliable DW introduction into magnetic wires. DW pinning is induced by a change of DW energy at an asymmetric single notch. The injection of DW from the circular pad and its pinning at the notch is observed by using AMR and magnetic force microscope (MFM) measurements. A four-point probe AMR measurement allows us to distinguish the DW type in the switching process because DWs are pinned at the single notch, where voltage probes are closely placed around the notch. Two types of AMR behavior are observed in the AMR measurements, which is owing to a change of DW structures. MFM images and micromagnetic simulations are consistent with the AMR results.

Thermomagnetic convection in a layer of ferrofluid placed in a uniform oblique external magnetic field

2015 ◽  
Vol 764 ◽  
pp. 316-348 ◽  
Author(s):  
Habibur Rahman ◽  
Sergey A. Suslov
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Additional Parameter ◽  
Thermomagnetic Convection ◽  
Uniform External Magnetic Field ◽  
Inclination Angles ◽  
Convection Patterns ◽  
The Stability ◽  
The Magnetic Field ◽  
Field Inclination

AbstractLinear stability of magnetoconvection of a ferromagnetic fluid contained between two infinite differentially heated non-magnetic plates in the presence of an oblique uniform external magnetic field is studied in zero gravity conditions. The thermomagnetic convection that arises is caused by the spatial variation of magnetisation occurring due to its dependence on the temperature. The critical values of the governing parameters at which the transition between motionless and convective states is observed are determined for various field inclination angles and for fluid magnetic parameters that are consistently chosen from a realistic experimental range. It is shown that, similar to natural paramagnetic fluids, the most prominent convection patterns align with the in-layer component of the applied magnetic field but in contrast to such paramagnetic fluids the instability patterns detected in ferrofluids can be oscillatory. It is also found that, contrary to paramagnetic fluids, the stability characteristics of magnetoconvection in ferrofluids depend on the magnitude of the applied field which becomes an additional parameter of the problem. This is shown to be due to the nonlinearity of the magnetic field distribution within the ferrofluid.

scholarly journals Transforming understanding of paleomagnetic recording: Insights from experimental observations of laboratory aged thermal remanences

2020 ◽  
Author(s):  
Lisa Tauxe ◽  
Christeanne Santos ◽  
Xiang Zhao ◽  
Andrew Roberts
Keyword(s):  
Magnetic Field ◽  
Domain Walls ◽  
Vortex State ◽  
Estimation Methods ◽  
Zero Field ◽  
Ideal Behavior ◽  
Temperature Spectrum ◽  
Single Vortex ◽  
Thermal Origin ◽  
The Stability

<p>Néel theory (doi: 10.1080/0001873550010120 ) predicts that natural remanent magnetizations (NRMs) of thermal origin will be nearly linearly related to the magnetic field in which they are acquired for field strenghts as low as the Earth's. This makes it in principle possible to estimate the strength of ancient magnetic fields. In practice, however, recovering the ancient field strength is complicated. The simple theory only pertains to uniformly magnetized (single domain, SD particles). While SD theory predicts that a magnetization acquired at a temperature T should be demagnetized by zero-field reheating to T, yet failure of this “reciprocity” requirement has long been observed and the causes and consequences for grains with no domain walls are unknown. Recent experiments (Shaar and Tauxe, doi: 10.1073/pnas.1507986112 and Santos and Tauxe, doi:10.1029/2018GC007946) have demonstrated that, in contrast to the stability of SD remanences over time, the remanence in many paleomagnetic samples typically used in paleointensity experiments are unstable, exhibiting an "aging" effect in which the unblocking temperature spectrum changes over only a few years.  This behavior is completely unexpected from theory. Solving these mysteries is key to cracking the problem of paleointensity estimation. In this presentation we will demonstrate that it is a shift in unblocking temperatures observed over even relatively short time intervals (two years) in certain samples that leads to the failure of reciprocity which in turn limits the ability to acquire accurate and precise estimates of the ancient magnetic field. From rock magnetic experiments (xFORCs) it seems likely that magnetic grains larger than the highly stable single vortex state are the source of the non-ideal behavior. This non-ideal behavior which leads to differences between known and estimated fields that can be rather large (up to 10 μT) for individual specimens, does appear to lead to a bias in field estimates.  It is unclear how this behavior can be compensated for using the most common paleointensity estimation methods.   </p>

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