scholarly journals Ultrasonic Study of Thermal hysteresis in Helical antiferromagnetic Dy

2018 ◽  
Vol 57 (2) ◽  
pp. 241-245 ◽  
Author(s):  
Iu. Liubimova ◽  
K. Sapozhnikov ◽  
V. Nikolaev ◽  
M.-Li Corró ◽  
S. Kustov
Keyword(s):  
Magnetic Field ◽  
Heating Rate ◽  
Applied Magnetic Field ◽  
Domain Walls ◽  
Thermal Hysteresis ◽  
Lattice Defects ◽  
Ferromagnetic Phase ◽  
Strong Increase ◽  
Ultrasonic Absorption ◽  
Thermal Cycles

Abstract High-resolution ultrasonic mechanical spectroscopy technique has been used to study the nature and dynamics of lattice defects and magnetic domain walls in the helical-type antiferromagnetic phase during thermal cycling of polycrystalline Dy samples between 80 and 210K. Effects of the lowest temperature of thermal cycles, applied magnetic field and cooling/ heating rate on the ultrasonic absorption and Young´s modulus have been investigated. A strong influence of cooling/heating rate on the ultrasonic absorption is found over the temperature range between the Néel temperature, ca. 178K, and approximately 145K, confirming the existence of a new category of magnetomechanical damping - transitory ultrasonic absorption related to translational motion of domain walls. A strong increase of the ultrasonic absorption below approximately 140K is attributed to the formation of nuclei of ferromagnetic phase, presumably stabilized by such lattice defects as dislocations. The effect of applied magnetic field on ultrasonic absorption also emerges below 140K and is ascribed to the appearance of the net magnetization due to ferromagnetic nuclei. We argue that these nuclei are responsible for the controversial thermal hysteresis of elastic and anelastic properties, which is strongly promoted by decreasing the temperature of thermal cycles.

The Influence of Magnetization on Corrosion in Pipeline Steels

2006 ◽  
Author(s):  
Joshua E. Jackson ◽  
Angelique N. Lasseigne-Jackson ◽  
Francisco J. Sanchez ◽  
David L. Olson ◽  
Brajendra Mishra
Keyword(s):  
Magnetic Field ◽  
Hydrogen Content ◽  
Applied Magnetic Field ◽  
Cold Work ◽  
Strong Increase ◽  
Surface Layers ◽  
Electronic Spin ◽  
Thermodynamic Effect ◽  
Hydrogen Induced Cracking ◽  
Anodic Reactions

Laboratory measurements have shown a strong increase on the hydrogen content in steel after electrochemical hydrogen charging with a two Tesla applied magnetic field and a serious increase in hydrogen-induced cracking and pitting. Cold work combining with the effect of applied magnetic field creates a material more crack sensitive to increased hydrogen content. A derivation based on the use of the Helmholtz Free Energy is applied to examine the thermodynamic effect of magnetization on hydrogen content. The effect of magnetization on the electronic spin configurations, magnetostriction (directional strain induced in steel from an applied magnetic field), and interstitial solute-induced strain are considered. A possible kinetic model for enhanced hydrogen ion pickup and corrosion based on surface effects associated with the Gouy-Chapman Layer and the Helmholtz Double Layer is examined. Disturbance of these layers acts to enhance hydrogen transport to the surface. The high applied and remanent magnetic fields and large cathodic protection currents returning in the pipe simultaneously may disturb these surface layers, resulting in enhancement of both cathodic and anodic reactions.

scholarly journals Transition from hydrodynamic turbulence to magnetohydrodynamic turbulence in von Kármán flows

2012 ◽  
Vol 693 ◽  
pp. 243-260 ◽  
Author(s):  
Gautier Verhille ◽  
Ruslan Khalilov ◽  
Nicolas Plihon ◽  
Peter Frick ◽  
Jean-François Pinton
Keyword(s):  
Magnetic Field ◽  
Reynolds Number ◽  
Interaction Parameter ◽  
Applied Magnetic Field ◽  
Strong Increase ◽  
Liquid Gallium ◽  
Induced Magnetic Field ◽  
Global Variables ◽  
Von Karman ◽  
Von Kármán

AbstractThe influence of an externally applied magnetic field on flow turbulence is investigated in liquid-gallium von-Kármán (VK) swirling flows. Time-resolved measurements of global variables (such as the flow power consumption) and local recordings of the induced magnetic field are made. From these measurements, an effective Reynolds number is introduced as ${\mathit{Rm}}_{\mathit{eff}} = \mathit{Rm}(1\ensuremath{-} \ensuremath{\alpha} \sqrt{N} )$, so as to take into account the influence of the interaction parameter $N$. This effective magnetic Reynolds number leads to unified scalings for both global variables and the locally induced magnetic field. In addition, when the flow rotation axis is perpendicular to the direction of the applied magnetic field, significant flow and induced magnetic field fluctuations are observed at low interaction parameter values, but corresponding to an Alfvèn speed ${v}_{A} $ of the order of the fluid velocity fluctuations ${u}_{\mathit{rms}} $. This strong increase in the flow fluctuations is attributed to chaotic changes between hydrodynamic and magnetohydrodynamic velocity profiles.

Lorentz microscopy study of magnetic domain walls in Fe-Cr-Co alloys

1978 ◽  
Vol 36 (1) ◽  
pp. 462-463
Author(s):  
Yalcin Belli
Keyword(s):  
Domain Walls ◽  
Magnetic Domain ◽  
Microscopy Study ◽  
Ferromagnetic Phase ◽  
Stable Phase ◽  
Magnetic Domains ◽  
Lorentz Microscopy ◽  
Magnetic Hardening ◽  
Electron Microscopes ◽  
Co Alloys

Fe-Cr-Co alloys have great technological potential to replace Alnico alloys as hard magnets. The relationship between the microstructures and the magnetic properties has been recently established for some of these alloys. The magnetic hardening has been attributed to the decomposition of the high temperature stable phase (α) into an elongated Fe-rich ferromagnetic phase (α1) and a weakly magnetic or non-magnetic Cr-rich phase (α2). The relationships between magnetic domains and domain walls and these different phases are yet to be understood. The TEM has been used to ascertain the mechanism of magnetic hardening for the first time in these alloys. The present paper describes the magnetic domain structure and the magnetization reversal processes in some of these multiphase materials. Microstructures to change properties resulting from, (i) isothermal aging, (ii) thermomagnetic treatment (TMT) and (iii) TMT + stepaging have been chosen for this investigation. The Jem-7A and Philips EM-301 transmission electron microscopes operating at 100 kV have been used for the Lorentz microscopy study of the magnetic domains and their interactions with the finely dispersed precipitate phases.

Imaging of ferroelectric domain walls by electron holography

1992 ◽  
Vol 50 (1) ◽  
pp. 246-247
Author(s):  
Xiao Zhang
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Domain Walls ◽  
Ferroelectric Domain ◽  
Object Wave ◽  
Electron Holography ◽  
High Resolution Imaging ◽  
Quantitative Measurements ◽  
Resolution Imaging ◽  
Electron Microscopes

Electron holography has recently been available to modern electron microscopy labs with the development of field emission electron microscopes. The unique advantage of recording both amplitude and phase of the object wave makes electron holography a effective tool to study electron optical phase objects. The visibility of the phase shifts of the object wave makes it possible to directly image the distributions of an electric or a magnetic field at high resolution. This work presents preliminary results of first high resolution imaging of ferroelectric domain walls by electron holography in BaTiO3 and quantitative measurements of electrostatic field distribution across domain walls.

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