Studies of Exchange Coupling in Fe (001) Whisker/Cr/Fe Structures using BLS and Rheed Techniques.

1993 ◽  
Vol 313 ◽  
Author(s):  
B. Heinrich ◽  
M. From ◽  
J.F. Cochran ◽  
L. X. Liao ◽  
Z. Celiński ◽  
...  
Keyword(s):  
Coupling Strength ◽  
Exchange Coupling ◽  
High Energy ◽  
Variable Number ◽  
Antiferromagnetic Coupling ◽  
Iron Film ◽  
First Principles Calculations ◽  
Iron Whisker ◽  
Short Period ◽  
Coupling Strengths

ABSTRACTThe conditions for an almost perfect growth of smooth Cr (001) films on an iron whisker substrate have been investigated by means of reflection high energy electron diffraction (RHEED). The exchange interaction between 20 Monolayer thick Fe (001) films separated from a bulk whisker Fe (001) substrate by a variable number of Cr (001) Monolayers (ML) has been investigated by means of Brillouin light scattering experiments (BLS). These experiments show unambiguously that the exchange coupling strength between the iron film and the iron whisker can be described by a short wavelength oscillatory term superposed on a slowly varying antiferromagnetic background. The BLS data enabled one to separate the bilinear and the biquadratic contributions to the antiferromagnetic exchange coupling terms. Both the bilinear and the biquadratic coupling strengths exhibited a short period oscillatory dependence on the Cr interlayer thickness (∼2 Monolayers). Maxima in the bilinear antiferromagnetic coupling strength occur for an odd number of Cr Monolayers. This observation is not in agreement with first principles calculations. The first phase inversion has been found to occur between 4 and 5 ML of Cr.

Bls Studies of Exchange Coupling in The Iron Whisker/Cr/Fe System

1995 ◽  
Vol 384 ◽  
Author(s):  
J.F. Cochran ◽  
K. Totland ◽  
B. Heinrich ◽  
D. Venus ◽  
S. Govorkov
Keyword(s):  
Thin Film ◽  
Coupling Strength ◽  
Kerr Effect ◽  
Exchange Coupling ◽  
Molecular Beam ◽  
Growth Conditions ◽  
Antiferromagnetic Coupling ◽  
Ferromagnetic Coupling ◽  
Film Magnetization

ABSTRACTBrillouin light scattering (BLS) and magneto-optic Kerr effect have been carried out on a series of specimens consisting of a Fe(001) whisker substrate upon which thin Cr(001) and Fe(001) layers have been deposited by means of molecular beam epitaxy in ultrahigh vacuum. The Fe film was 20 monolayers (ML) thick, and the Cr(001) films were grown having various thicknesses. It is demonstrated that BLS thin film frequencies measured in the saturated magnetic state with the thin film magnetization parallel with the applied magnetic field can be used to obtain the exchange coupling strength between the thin film and whisker magnetizations both for antiferromagnetic coupling and for ferromagnetic coupling, provided that the ferromagnetic coupling is not too strong. It is also shown that the coupling strength is extremely sensitive to the quality of the chromium growth: a small deterioration in the growth conditions has been found to reduce the exchange coupling by nearly a factor of two.

scholarly journals Dependence of Atomic Thickness on Interfacial Conditions and Magnetocrystalline Anisotropy in SmCo5/Sm2Co17 Multilayer

2018 ◽  
Author(s):  
Soyoung Jekal
Keyword(s):  
Atomic Structure ◽  
Coupling Strength ◽  
First Principles ◽  
Exchange Coupling ◽  
Magnetocrystalline Anisotropy ◽  
Model Systems ◽  
First Principles Calculations ◽  
Magnetic Structures ◽  
Multilayer Model ◽  
Interfacial Conditions

We have performed first-principles calculations to study the interfacial exchange coupling and magnetocrystalline anisotropy (MCA) energy in a SmCo5/Sm2Co17 multilayer model systems. The phase of SmCo5 and Sm2Co17 stacking along (0001) direction are structurally well matched. The atomic structure, including the alignment and the separation between layers, were firstly optimized. Then the non-collinear magnetic structures were calculated to explore the exchange coupling across the interface and the variation of MCA energy. We found that the inter-phase exchange coupling strength, rotating behavior and MCA energy are strongly dependent on the atomic thickness of the SmCo5 and Sm2Co17 phase.

scholarly journals Dependence of Atomic Thickness on Interfacial Conditions and Magnetocrystalline Anisotropy in SmCo5/Sm2Co17 Multilayer

Materials ◽  
2018 ◽  
Vol 12 (1) ◽  
pp. 56
Author(s):  
Soyoung Jekal
Keyword(s):  
Coupling Strength ◽  
First Principles ◽  
Exchange Coupling ◽  
Magnetocrystalline Anisotropy ◽  
Model System ◽  
Anisotropy Energy ◽  
First Principles Calculations ◽  
Magnetic Structures ◽  
Interfacial Conditions ◽  
Magnetocrystalline Anisotropy Energy

We have performed first-principles calculations to study the interfacial exchange coupling and magnetocrystalline anisotropy energy in a SmCo 5 /Sm 2 Co 17 multilayer model system. The phase of SmCo 5 and Sm 2 Co 17 stacking along (0001) direction are structurally well matched. The atomic structure, including the alignment and the separation between layers, were firstly optimized. Then the non-collinear magnetic structures were calculated to explore the exchange coupling across the interface and the variation of magnetocrystalline anisotropy energy. We found that the inter-phase exchange coupling strength, rotating behavior and magnetocrystalline anisotropy strongly depend on the atomic thickness of the SmCo 5 and Sm 2 Co 17 phase.

A Study of Exchange-Coupling Effect on Nd2Fe14B / α-Fe Forming Core/Shell Shape

2007 ◽  
Vol 119 ◽  
pp. 147-150 ◽  
Author(s):  
Chang Woo Kim ◽  
Young Hwan Kim ◽  
Don Keun Lee ◽  
In Chul Jeong ◽  
Hae Woong Kwon ◽  
...  
Keyword(s):  
Exchange Coupling ◽  
Ball Mill ◽  
Coupling Effect ◽  
Chemical Reduction ◽  
High Energy ◽  
Shell Shape ◽  
Core Shell ◽  
High Energy Ball Mill ◽  
Energy Ball ◽  
Mill Process

We report the core/shell type as the interesting one of the various techniques to prepare exchange-coupled permanent magnet. In this study, the exchange-coupled Nd2Fe14B/α-Fe was prepared by high energy ball mill process and chemical reduction. Nd15Fe77B8 powder prepared by high energy ball mill process was coated with α-Fe nanoparticle by chemical reduction. α-Fe nanoparticle on the ball milled Nd15Fe77B8 was synthesized by chemical reduction with borohydride as a reducing agent in aqueous solution. After annealing, Nd2Fe14B/α-Fe forming core/shell shape has exchange-coupling effect and was identified by using XRD, FE-SEM, VSM, TMA and EDX.

scholarly journals Dynamics of the Askja caldera July 2014 landslide, Iceland, from seismic signal analysis: precursor, motion and aftermath

2017 ◽  
Author(s):  
Anne Schöpa ◽  
Wei-An Chao ◽  
Bradley Lipovsky ◽  
Niels Hovius ◽  
Robert S. White ◽  
...  
Keyword(s):  
Seismic Data ◽  
Signal Analysis ◽  
Slope Failure ◽  
Stable State ◽  
Seismic Signal ◽  
Early Warning Systems ◽  
High Energy ◽  
Stick Slip ◽  
Short Period ◽  
Large Landslide

Abstract. Using data from a network of 58 seismic stations, we characterise a large landslide that occurred at the southeastern corner of the Askja caldera, Iceland, on 21 July 2014, including its precursory tremor and mass wasting aftermath. Our study is motivated by the need for deeper generic understanding of the processes operating not only at the time of catastrophic slope failure, but also in the preparatory phase and during the transient into the subsequent stable state. In addition, it is prompted by the high hazard potential of the steep caldera lake walls at Askja as tsunami waves created by the landslide reached famous tourist spots 60 m above the lake level. Since direct observations of the event are lacking, the seismic data give valuable details on the dynamics of this landslide episode. The excellent seismic data quality and coverage of the stations of the Askja network made it possible to jointly analyse the long- and short-period signals of the landslide to obtain information about the triggering, initiation, timing, and propagation of the slide. The seismic signal analysis and a landslide force history inversion of the long-period seismic signals showed that the Askja landslide was a single, large event starting at the SE corner of the caldera lake at 23:24:05 UTC and propagating to the NW in the following 2 min. The bulk sliding mass was 7–16 × 1010 kg, equivalent to a collapsed volume of 35–80 × 106 m3, and the centre of mass was displaced horizontally downslope by 1260 ± 250 m during landsliding. The seismic records of stations up to 30 km away from the landslide source area show a tremor signal that started 30 min before the main landslide failure. It is harmonic, with a fundamental frequency of 2.5 Hz and shows time-dependent changes of its frequency content. We attribute the complex tremor signal to accelerating and decelerating stick-slip motion on failure planes at the base and the sides of the landslide body. The accelerating motion culminated in aseismic slip of the landslide visible as a drop in the seismic amplitudes down to the background noise level 2 min before the landslide high-energy signal begins. We propose that the seismic signal of the precursory tremor may be developed as an indicator for landslide early-warning systems. The 8 hours after the main landslide failure are characterised by smaller slope failures originating from the destabilised caldera wall decaying in frequency and magnitude. We introduce the term afterslides for this subsequent, declining slope activity after a large landslide.

Studies of Exchange Coupling in Fe/Cu/Fe(001) “Loose Spin” Structures

1995 ◽  
Vol 384 ◽  
Author(s):  
M. Kowalewski ◽  
B. Heinrich ◽  
K. Totland ◽  
J.F. Cochran ◽  
S. Govorkov ◽  
...  
Keyword(s):  
Exchange Coupling ◽  
Interlayer Coupling ◽  
Antiferromagnetic Coupling ◽  
Concentration Limit ◽  
Interlayer Exchange Coupling ◽  
High Concentration ◽  
Significant Difference ◽  
Valence Electrons ◽  
Interlayer Exchange

ABSTRACTThe interlayer exchange coupling has been studied in two trilayer structures:(a) 5.7Fe/5Cu/1FecCu1-c/5Cu/10Fe(001), where c=0.0, 0.1, 0.2, 0.45 0.60(b) 5.7Fe/5Cu/1CrcCu1-c/5Cu/10Fe(001), where c=0.1, 0.45, 0.8 and 1.0.The intention of these studies was to identify the role of Fe and Cr atoms in the alloyed FecCu1-c and CrcCu1-c layers on the direct interlayer coupling which is facilitated by the Cu valence electrons. FMR, BLS and MOKE studies were used to determine the interlayer exchange coupling. Mossbauer spectroscopy was used to identify the magnetic state of the Fe atoms in the alloyed layer. The results showed that the presence of foreign atoms inside the Cu spacer significantly decreased the bilinear antiferromagnetic coupling between the Fe layers. In the low concentration limit the Fe and Cr atoms behaved in a similar manner. A significant difference was found in the high concentration limit where the Fe atoms start to be partially magnetically ordered.

EVOLUTION OF ATOM-FIELD PROBABILITY IN A COUPLED CAVITY SYSTEM

2013 ◽  
Vol 22 (03) ◽  
pp. 1350029
Author(s):  
K. V. PRIYESH ◽  
RAMESH BABU THAYYULLATHIL
Keyword(s):  
Coupling Strength ◽  
Probability Amplitude ◽  
Field Coupling ◽  
Level Atom ◽  
Cavity System ◽  
Coupling Strengths ◽  
Field Excitation ◽  
Excitation Probability ◽  
Hopping Strength ◽  
Coupled Cavity

In this paper we have investigated the dynamics of two cavities each with a two-level atom, coupled together with photon hopping. The coupled cavity system is studied in single excitation subspace and the evolution of the atom (field) states probabilities are obtained analytically. The probability amplitude of states executes oscillations with different modes and amplitudes, determined by the coupling strengths. The evolution is examined in detail for different atom field coupling strength, g and field–field hopping strength, A. It is noticed that the exact atomic probability amplitude transfer occurs when g ≪ A with minimal field excitation probability and the period of probability transfer is calculated. In the limit g ≫ A there exists periodic exchange of probability between atom and field inside each cavity and also between cavity 1 and cavity 2. Periodicity of each exchange in this limit also obtained.

scholarly journals Magnetic Properties of SmCo5 + 10 wt% Fe Exchange-Coupled Nanocomposites Produced from Recycled SmCo5

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1308 ◽  
Author(s):  
Arnab Chakraborty ◽  
Răzvan Hirian ◽  
Gregor Kapun ◽  
Viorel Pop
Keyword(s):  
Heat Treatment ◽  
Exchange Coupling ◽  
Permanent Magnets ◽  
High Energy ◽  
Raw Material ◽  
Energy Ball ◽  
Hydrogen Decrepitation ◽  
Energy Products ◽  
First Time ◽  
Recycled Material

Nanostructured alloy powders of SmCo5 + 10 wt% Fe obtained using recycled material were studied for the first time. The SmCo5 precursor was obtained from commercial magnets recycled by hydrogen decrepitation. The results were compared with identically processed samples obtained using virgin SmCo5 raw material. The samples were synthesized by dry high-energy ball-milling and subsequent heat treatment. Robust soft/hard exchange coupling was observed—with large coercivity, which is essential for commercial permanent magnets. The obtained energy products for the recycled material fall between 80% and 95% of those obtained when using virgin SmCo5, depending on milling and annealing times. These results further offer viability of recycling and sustainability in production. These powders and processes are therefore candidates for the next generation of specialized and nanostructured exchange-coupled bulk industrial magnets.

scholarly journals Investigation of the WR 11 field at decimeter wavelengths

2019 ◽  
Vol 625 ◽  
pp. A99 ◽  
Author(s):  
P. Benaglia ◽  
S. del Palacio ◽  
C. H. Ishwara-Chandra ◽  
M. De Becker ◽  
N. L. Isequilla ◽  
...  
Keyword(s):  
Spectral Index ◽  
Thermal Emission ◽  
Mass Loss Rate ◽  
High Energy ◽  
Low Frequencies ◽  
Nonthermal Radio ◽  
Short Period ◽  
Radiation Processes ◽  
Period System ◽  
The Individual

The massive binary system WR 11 (γ2-Velorum) has recently been proposed as the counterpart of a Fermi source. If this association is correct, this system would be the second colliding wind binary detected in GeV γ-rays. However, the reported flux measurements from 1.4 to 8.64 GHz fail to establish the presence of nonthermal (synchrotron) emission from this source. Moreover, WR 11 is not the only radio source within the Fermi detection box. Other possible counterparts have been identified in archival data, some of which present strong nonthermal radio emission. We conducted arcsec-resolution observations toward WR 11 at very low frequencies (150–1400 MHz) where the nonthermal emission – if existent and not absorbed – is expected to dominate. We present a catalog of more than 400 radio emitters, among which a significant portion are detected at more than one frequency, including limited spectral index information. Twenty-one of these radio emitters are located within the Fermi significant emission. A search for counterparts for this last group pointed at MOST 0808–471; this source is 2′ away from WR 11 and is a promising candidate for high-energy emission, having a resolved structure along 325–1390 MHz. For this source, we reprocessed archive interferometric data up to 22.3 GHz and obtained a nonthermal radio spectral index of − 0.97 ± 0.09. However, multiwavelength observations of this source are required to establish its nature and to assess whether it can produce (part of) the observed γ-rays. WR 11 spectrum follows a spectral index of 0.74 ± 0.03 from 150 to 230 GHz, consistent with thermal emission. We interpret that any putative synchrotron radiation from the colliding-wind region of this relatively short-period system is absorbed in the photospheres of the individual components. Notwithstanding, the new radio data allowed us to derive a mass-loss rate of 2.5 × 10−5 M⊙ yr−1, which, according to the latest models for γ-ray emission in WR 11, would suffice to provide the required kinetic power to feed nonthermal radiation processes.

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