scholarly journals Transverse susceptibility of nickel thin films with uniaxial anisotropy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Scott A. Mathews ◽  
Christopher Musi ◽  
Nicholas Charipar
Keyword(s):  
Applied Field ◽  
Magnetic State ◽  
Uniaxial Anisotropy ◽  
Simulated Data ◽  
Anisotropy Field ◽  
Absolute Value ◽  
Hard Axis ◽  
Nickel Thin Films ◽  
Low Temperature Annealing ◽  
Theoretical Predictions

AbstractA finite temperature Stoner–Wohlfarth model has been used to calculate the transverse susceptibility of an ensemble of ferromagnetic particles with distributed anisotropy. The simulated transverse susceptibility is in excellent agreement with data acquired from thin film samples of elemental nickel, deposited on 128° Y-cut LiNb03. A strong, well-defined, uniaxial anisotropy is induced in the nickel film by low temperature annealing. Three peaks in the transverse susceptibility are observed in both the measured and simulated data when the applied field is misaligned with the hard axis by a few degrees. Two broad, reversible peaks occur when the applied field is equal to the anisotropy field. A single, sharp irreversible peak occurs when the absolute value of the applied field is less than the anisotropy field, and is associated with a metastable magnetic state. The irreversible peak disappears when the applied field is well aligned with the hard axis. The observed transverse susceptibility is consistent with the theoretical predictions of Aharoni et al. and is therefore consistent with the Stoner–Wohlfarth model.

scholarly journals Dynamics of Magnetization in Multilayer TbCo / FeCo Structures under the Influence of Femtosecond Optical Excitation

2019 ◽  
Vol 7 (3) ◽  
pp. 50-58 ◽  
Author(s):  
N. A. Ilyin ◽  
A. A. Klimov ◽  
N. Tiercelin ◽  
P. Pernod ◽  
E. D. Mishina ◽  
...  
Keyword(s):  
Easy Axis ◽  
Uniaxial Anisotropy ◽  
Anisotropy Field ◽  
Optical Excitation ◽  
Spin Precession ◽  
Heat Diffusion ◽  
Easy Magnetization ◽  
Test Beam ◽  
Magnetic Subsystem ◽  
Hard Axis

The need to study ultrafast processes in magnetism is due to the prospects for creating ultrafast magnetic recording and ultrafast spintronic devices. In order to excite the magnetic subsystem femtosecond optical pulses are used. The excitement is manifested as in spin precession. In metals, the material is heated first due to significant optical absorption, and significant Joule losses occur. The most important task is to search for materials in which spin processes are excited without heating. Obvious candidates are weakly absorbing materials, such as ferrite garnets. However, the range of such materials and the range of their functionality are limited.The purpose of this work is to study the dynamics of systems with nonthermal mechanisms of spin precession excitation. Such excitation is possible in ferromagnetic / antiferromagnetic heterostructures with exchange interaction, provided that the recombination time of photocarriers is shorter than the time of heat diffusion. Multilayer TbCo / FeCo structures of the near IR range were investigated for a femtosecond optical pulse. The spin dynamics are compared with the direction of the wave vector of the exciting pulse along and perpendicular to the axis of easy magnetization of the structures (“easy axis” and “hard axis” geometry, respectively). It is shown that in case of “easy axis” geometry the determinative mechanism is the thermal interaction. When the system is exposed to an excitation pulse, this mechanism leads to a decrease in the projection of magnetization on the direction of propagation of the test beam. In case of “hard axis” geometry, the magnetization turns to the magnetic field at the initial stage. Then it precesses and relaxes to an equilibrium angular orientation. Such dynamics indicate a rapid recovery of the uniaxial anisotropy field after laser irradiation. The presented results demonstrate an ultrafast change in the magnetic anisotropy induced during the fabrication of the heterostructure under study, which may be of interest for optical control of the orientation of the magnetization.

Contact resistance, coupling and hysteresis loss measurements of ITER Poloidal Field joint in parallel applied magnetic field

2021 ◽  
Author(s):  
Jianfeng Huang ◽  
Y. Ilyin ◽  
W.A.J. Wessel ◽  
Ruben Lubkemann ◽  
Erik Krooshoop ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Contact Resistance ◽  
Applied Magnetic Field ◽  
Applied Field ◽  
Simulated Data ◽  
Hysteresis Loss ◽  
Ac Loss ◽  
Field Conditions ◽  
Ac Losses ◽  
First Time

Abstract The inter-strand contact resistance and AC losses were measured on an ITER PF Coil joint in a parallel applied AC magnetic field. In addition, the hysteresis loss was measured as a function of the angle with the applied magnetic field on a NbTi strand of the same type as in the joint with a Vibrating Sample Magnetometer (VSM). The AC loss measurements were performed at four applied field conditions for combinations of 0 or 1 T offset field and 0.2 or 0.4 T sinusoidal amplitude. The hysteresis loss of the joint was compared with the measured AC loss density of the NbTi strand for the same field conditions as the joint AC loss measurement but with varying the angle of the applied field. The subsequent cable twist angles affect the hysteresis loss since the critical current and penetration field depend on the angle of the applied field. It is found that 15.5° is an effective angle for the calculation of the hysteresis loss of joint when compared to the single strand measurement. The inter-strand contact resistance measurements cover all the typical strand combinations from the five cabling stages of the individual conductors, as well as the strand combinations across the two conductors to characterize the inter-strand including the copper sole resistivity. It’s the first time to measure the contact resistances and AC losses of the full-size ITER PF joint. By comparing the measured and simulated data in the JackPot-ACDC model, it’s also the first time to obtain the accurate inter-strand, inter-petal and strand to copper sole contact resistivities, which are the main input parameters for the further quantitative numerical analysis of the PF joints, in any current and magnetic field conditions.

scholarly journals Anticipating the emergence of infectious diseases

2017 ◽  
Vol 14 (132) ◽  
pp. 20170115 ◽  
Author(s):  
Tobias S. Brett ◽  
John M. Drake ◽  
Pejman Rohani
Keyword(s):  
Large Scale ◽  
Simulated Data ◽  
Disease Emergence ◽  
General Applicability ◽  
Slowing Down ◽  
Animal Populations ◽  
Theoretical Predictions ◽  
Parameter Values ◽  
Model Structures ◽  
Good Support

In spite of medical breakthroughs, the emergence of pathogens continues to pose threats to both human and animal populations. We present candidate approaches for anticipating disease emergence prior to large-scale outbreaks. Through use of ideas from the theories of dynamical systems and stochastic processes we develop approaches which are not specific to a particular disease system or model, but instead have general applicability. The indicators of disease emergence detailed in this paper can be classified into two parallel approaches: a set of early-warning signals based around the theory of critical slowing down and a likelihood-based approach. To test the reliability of these two approaches we contrast theoretical predictions with simulated data. We find good support for our methods across a range of different model structures and parameter values.

scholarly journals Microstructures and Soft Magnetic Properties of High Saturation Magnetization Fe-Co-N alloy Thin Films

2000 ◽  
Vol 614 ◽  
Author(s):  
N. X. Sun ◽  
S. X. Wang ◽  
Chin-Ya Hung ◽  
Chester X. Chien ◽  
Hua-Ching Tong
Keyword(s):  
Saturation Magnetization ◽  
Easy Axis ◽  
Uniaxial Anisotropy ◽  
Single Layer ◽  
Soft Magnetic Materials ◽  
High Saturation Magnetization ◽  
Soft Magnetic ◽  
Hard Axis ◽  
High Saturation ◽  
Significant Difference

ABSTRACTHigh saturation magnetization soft magnetic materials are required for future high-density recording heads as well as high frequency inductors. In this work, (Fe0.7Co0.3)1−xNx (or in short FeCoN) alloy films were synthesized with a high saturation magnetization of 24.5 kG, a hard axis coercivity of 5 Oe, an easy axis coercivity of 18 Oe, and a resistivity of 55 μΩcm. The FeCoN film sandwiched between two permalloy layers (5 nm) shows very good magnetic softness, a low hard axis coercivity of 0.6 Oe, an easy axis coercivity of 7.8 Oe, an excellent in-plane uniaxial anisotropy with an anisotropy of about 20 Oe, an initial permeability of 1000, and a roll-off frequency of 1.5 GHz. In order to understand the effect of the permalloy layers on the FeCoN layer, we fabricated four film structures: single layer FeCoN film; FeCoN film sandwiched between two permalloy layers on both sides; FeCoN film with one permalloy layer as the underlayer; and FeCoN film with one permalloy layer as caplayer. All these film structures were both magnetically and structurally characterized and compared. Structural characterization shows that there is no significant difference in the grain size of the FeCoN single layer and the FeCoN layer sandwiched between two permalloy layers. The four film structures have almost the same amount of compressive stress, about −300 MPa; and their saturation magnetostriction constants are also very close, in the range of 39.6×10−6 to 44.3×10−6. Difference in the crystallographic textures was observed in the pole figures for the FeCoN single layer and FeCoN film with permalloy underlayer.

Ac Susceptibility Studies of New and Familiar Magnetic Molecular Solids

1997 ◽  
Vol 488 ◽  
Author(s):  
Roger D. Sommer ◽  
Brenda J. Korte ◽  
Scott P. Sellers ◽  
Gordon T. Yee
Keyword(s):  
Applied Field ◽  
Magnetic State ◽  
Ac Susceptibility ◽  
Strong Dependence ◽  
Single Frequency ◽  
Molecular Solids ◽  
Standard Practice ◽  
Susceptibility Data ◽  
Ac Susceptometry ◽  
Molecular Solid

Abstractac Susceptometry has been used to study a number of magnetic molecular solids including a new compound, Mn(II) octaethyltetraazaporphyrin, α-MnOETAP, and decamethylmanganocenium tetracyanoethenide, Mn(Cp*)2•TCNE, a previously reported molecule-based ferromagnet. Both of these compounds exhibit signatures of ferromagnetism including significant hysteresis below 2 K and rapidly increasing χT (where χ is the molar susceptibility) with decreasing temperature. However, their ac susceptibility data show relatively strong dependence of χ′ and χ″ on the frequency of the applied field, indicating a spinglass state. Other molecular ferromagnetic solids examined show much less sensitivity. These studies indicate that the standard practice of characterization by dc and ac susceptometry at a single frequency are clearly insufficient for identifying the magnetic state of a molecular solid.

Probing Arrays of Circular Magnetic Microdots by Ferromagnetic Resonance

2008 ◽  
Vol 8 (6) ◽  
pp. 2811-2826 ◽  
Author(s):  
G. N. Kakazei ◽  
T. Mewes ◽  
P. E. Wigen ◽  
P. C. Hammel ◽  
A. N. Slavin ◽  
...  
Keyword(s):  
Ferromagnetic Resonance ◽  
Quantitative Description ◽  
Uniaxial Anisotropy ◽  
Anisotropy Field ◽  
Iterative Solution ◽  
Wave Dispersion ◽  
Square Lattice ◽  
Rectangular Lattice ◽  
Force Microscopy ◽  
Good Agreement

X-band ferromagnetic resonance (FMR) was used to characterize in-plane magnetic anisotropies in rectangular and square arrays of circular nickel and Permalloy microdots. In the case of a rectangular lattice, as interdot distances in one direction decrease, the in-plane uniaxial anisotropy field increases, in good agreement with a simple theory of magnetostatically interacting uniformly magnetized dots. In the case of a square lattice a four-fold anisotropy of the in-plane FMR field Hr was found when the interdot distance a gets comparable to the dot diameter D. This anisotropy, not expected in the case of uniformly magnetized dots, was explained by a non-uniform magnetization m(r) in a dot in response to dipolar forces in the patternedmagnetic structure. It is well described by an iterative solution of a continuous variation procedure. In the case of perpendicular magnetization multiple sharp resonance peaks were observed below the main FMR peak in all the samples, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance FMR spectra was given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account. It was demonstrated that ferromagnetic resonance force microscopy (FMRFM) can be used to determine both local and global properties of patterned submicron ferromagnetic samples. Local spectroscopy together with the possibility to vary the tip-sample spacing enables the separation of those two contributions to a FMRFM spectrum. The global FMR properties of circular submicron dots determined using magnetic resonance force microscopy are in a good agreement with results obtained using conventional FMR and with theoretical descriptions.

Sign in / Sign up

Export Citation Format

Share Document