scholarly journals Magnetic relaxation dynamics driven by the first-order character of magnetocaloric La(Fe,Mn,Si) 13

2016 ◽  
Vol 374 (2074) ◽  
pp. 20150307 ◽  
Author(s):  
Edmund Lovell ◽  
Milan Bratko ◽  
A. David Caplin ◽  
Alexander Barcza ◽  
Matthias Katter ◽  
...  
Keyword(s):  
Temporal Dynamics ◽  
Magnetic Hysteresis ◽  
Relative Magnitude ◽  
Zero Field ◽  
Ferromagnetic Transition ◽  
Relaxation Dynamics ◽  
First Order ◽  
Temperature Separation ◽  
The Magnetic Field ◽  
Field Transition

Here, we study the temporal evolution of the magnetic field-driven paramagnetic to ferromagnetic transition in the La(Fe,Mn,Si) 13 material family. Three compositions are chosen that show varying strengths of the first-order character of the transition, as determined by the relative magnitude of their magnetic hysteresis and temperature separation between the zero-field transition temperature T c and the temperature T crit , where the transition becomes continuous. Systematic variations in the fixed field, isothermal rate of relaxation are observed as a function of temperature and as a function of the degree of first-order character. The relaxation rate is reduced in more weakly first-order compositions and is also reduced as the temperature is increased towards T crit . At temperatures above T crit , the metastability of the transition vanishes along with its associated temporal dynamics. This article is part of the themed issue ‘Taking the temperature of phase transitions in cool materials’.

scholarly journals Reversibility of the Magnetocaloric Effect in the Bean-Rodbell Model

2021 ◽  
Vol 7 (5) ◽  
pp. 60
Author(s):  
Luis M. Moreno-Ramírez ◽  
Victorino Franco
Keyword(s):  
Magnetic Field ◽  
Thermal Hysteresis ◽  
Entropy Change ◽  
Second Order ◽  
Zero Field ◽  
First Order ◽  
Magnetic Field Change ◽  
Magnetocaloric Materials ◽  
Moderate Magnetic Field ◽  
The Magnetic Field

The applicability of magnetocaloric materials is limited by irreversibility. In this work, we evaluate the reversible magnetocaloric response associated with magnetoelastic transitions in the framework of the Bean-Rodbell model. This model allows the description of both second- and first-order magnetoelastic transitions by the modification of the η parameter (η<1 for second-order and η>1 for first-order ones). The response is quantified via the Temperature-averaged Entropy Change (TEC), which has been shown to be an easy and effective figure of merit for magnetocaloric materials. A strong magnetic field dependence of TEC is found for first-order transitions, having a significant increase when the magnetic field is large enough to overcome the thermal hysteresis of the material observed at zero field. This field value, as well as the magnetic field evolution of the transition temperature, strongly depend on the atomic magnetic moment of the material. For a moderate magnetic field change of 2 T, first-order transitions with η≈1.3−1.8 have better TEC than those corresponding to stronger first-order transitions and even second-order ones.

Oscillatory Angular Dependence of Exchange Bias for Epitaxial NiO-Co (001) Bilayers

2001 ◽  
Vol 674 ◽  
Author(s):  
S. Dubourg ◽  
J.F. Bobo ◽  
B. Warot ◽  
E. Snoeck ◽  
J.C. Ousset
Keyword(s):  
Magnetic Field ◽  
Exchange Bias ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
Field Application ◽  
Zero Field ◽  
Sign Change ◽  
Realistic Description ◽  
Sputter Deposited ◽  
The Magnetic Field

ABSTRACTWe have sputter-deposited NiO-Co bilayers on MgO (001) substrates. NiO grows epitaxially on MgO at 900°C and subsequently the room deposited 80 Åthick Co films have a fcc crystal structure in epitaxy with the oxide underlayer. These samples were warmed up to 300° C and then zero-field or field cooled through the NiO Néel temperature (a 300 Oe magnetic field was applied along the [100] or the [110] MgO axis). Magnetic hysteresis loops were obtained by magneto-optical Kerr effect, the magnetic field being oriented in the plane of the substrate for various angles α with respect to the [100] direction. The usually expected behavior for such experiments is a smooth angular α dependence of the exchange bias HE close to a cosine with only one sign change over 180°. The high crystallographic coherence of our NiO/Co bilayers induces a very unusual oscillatory HE (α) dependence with several sign changes according to the NiO axis field application. Despite of the Co magnetization switching mechanism which is not a pure coherent rotation, we propose a Stoner-Wohlfhart model including four fold anisotropy and unidirectional exchange anisotropy giving a realistic description of these typical magnetic properties.

Flux-Flow and Fluctuations in the Microwave Resistivity of YBa2Cu3O7-δ

1999 ◽  
Vol 13 (09n10) ◽  
pp. 1107-1110 ◽  
Author(s):  
E. Silva ◽  
D. Neri ◽  
R. Marcon ◽  
R. Fastampa ◽  
M. Giura ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Coherence Length ◽  
Quantitative Description ◽  
Zero Field ◽  
Flux Flow ◽  
Flux Dynamic ◽  
Dissipative Mechanism ◽  
The Magnetic Field ◽  
Microwave Resistivity ◽  
Field Transition

We present measurements of the microwave resistivity at 48 GHz in YBa 2 Cu 3 O 7-δ film, as a function of the temperature and the magnetic field. The magneto-dissipation from 60 K up to a few kelvins below Tc finds a quantitative description in terms of free flux flow. Approaching Tc, the data are not consistent with a dissipative mechanism based solely on flux dynamic. Fluxon viscosity is measured as a function of the temperature, and the in-plane coherence length is estimated. The analysis of the zero-field transition at 48 GHz in terms of anisotropic renormalized fluctuations yields identical estimate.

Doppler-Shifted Cyclotron Resonance in Thin Metal Films

1972 ◽  
Vol 50 (18) ◽  
pp. 2122-2137
Author(s):  
R. Turner ◽  
J. F. Cochran
Keyword(s):  
Magnetic Field ◽  
Metal Films ◽  
Thin Metal Film ◽  
Thin Metal ◽  
Free Electrons ◽  
Fermi Surfaces ◽  
First Order ◽  
Simple Quantum ◽  
The Magnetic Field ◽  
Good Agreement

According to Van Gelder the microwave absorption by a thin metal film in the presence of a static magnetic field normal to the film contains a series of peaks as the magnetic field is varied. In the present paper it is argued that these peaks correspond to Doppler-shifted cyclotron resonances of the carriers in the metal due to the quantization of electron momenta normal to the plane of the film. A simple quantum calculation is presented for the case of free electrons where the film is thin enough that to first order the microwave fields within are determined only by the boundary conditions and Maxwell's equations. The quantum expression is in good agreement with the absorption calculated using semiclassical arguments which can be readily extended to more complicated Fermi surfaces.

FORC analysis of magnetically soft microparticles embedded in a polymeric elastic environment

2022 ◽  
Author(s):  
Dmitry Yu Borin ◽  
Mikhail V Vaganov
Keyword(s):  
Particle Concentration ◽  
Magnetic Hysteresis ◽  
Magnetic Response ◽  
Soft Matrix ◽  
First Order ◽  
Matrix Elasticity ◽  
Intrinsic Coercivity ◽  
The Matrix ◽  
Soft Particles ◽  
Elastomer Composites

Abstract First-order reversal curve (FORC) analysis allows one to investigate composite magnetic materials by decomposing the magnetic response of a whole sample into individual responses of the elementary objects comprising the sample. In this work, we apply this technique to analysing silicone elastomer composites reinforced with ferromagnetic microparticles possessing low intrinsic coercivity. Even though the material of such particles does not demonstrate significant magnetic hysteresis, the soft matrix of the elastomers allows for the translational mobility of the particles and enables their magnetomechanical hysteresis which renders into a wasp-waisted major magnetization loop of the whole sample. It is demonstrated that the FORC diagrams of the composites contain characteristic wing features arising from the collective hysteretic magnetization of the magnetically soft particles. The influence of the matrix elasticity and particle concentration on the shape of the wing feature is investigated, and an approach to interpreting experimental FORC diagrams of the magnetically soft magnetoactive elastomers is proposed. The experimental data are in qualitative agreement with the results of the simulation of the particle magnetization process obtained using a model comprised of two magnetically soft particles embedded in an elastic environment.

High magnetic field NMR investigation of the spin density wave phase of TMTSF2PF6

2002 ◽  
Vol 12 (9) ◽  
pp. 389-389
Author(s):  
W. G. Clark ◽  
F. Zamborsky ◽  
B. Alavi ◽  
P. Vonlanthen ◽  
W. Moulton ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spin Density ◽  
Density Wave ◽  
Spin Density Wave ◽  
Proton Relaxation ◽  
High Magnetic Fields ◽  
Organic Conductor ◽  
First Order ◽  
The Magnetic Field ◽  
Very High

We report proton NMR measurements of the effect of very high magnetic fields up to 44.7 T (1.9 GHz) on the spin density wave (SDW) transition of the organic conductor TMTSF2PF6. Up to 1.8 GHz, no effect of critical slowing close to the transition is seen on the proton relaxation rate (1/T1), which is determined by the SDW fluctuations associated with the phase transition at the NMR frequency. Thus, the correlation time for such fluctuations is less than $1O^{-10}$s. A possible explanation for the absence of longer correlation times is that the transition is weakly first order, so that the full critical divergence is never achieved. The measurements also show a dependence of the transition temperature on the orientation of the magnetic field and a quadratic dependence on its magnitude that agrees with earlier transport measurements at lower fields. The UCLA part of this work was supported by NSF Grant DMR-0072524.

Zero-Field Level Crossing in the Helium Atom

1972 ◽  
Vol 50 (2) ◽  
pp. 116-118 ◽  
Author(s):  
C. W. T. Chien ◽  
R. E. Bardsley ◽  
F. W. Dalby
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Helium Atom ◽  
Cross Sections ◽  
Zero Field ◽  
Level Crossing ◽  
Field Level ◽  
Collision Cross Sections ◽  
The Magnetic Field

Zero-field level-crossing techniques have been used to measure some upper-state lifetimes of the helium atom. The half-widths of curves obtained by plotting the polarization against the magnetic field strength for the n1D–21D transitions yielded lifetimes of 2.03 × 10−8 s for the 31D state, 3.36 × 10−8 s for the 41D state, and 7.44 × 10−8 s for the 51D state. Collision cross sections for these 1D levels were also determined.

A METAMAGNETIC QUANTUM CRITICAL ENDPOINT IN Sr3Ru2O7

2002 ◽  
Vol 16 (20n22) ◽  
pp. 3258-3264 ◽  
Author(s):  
S. A. GRIGERA ◽  
A. P. MACKENZIE ◽  
A. J. SCHOFIELD ◽  
S. R. JULIAN ◽  
G. G. LONZARICH
Keyword(s):  
Quantum Critical Point ◽  
Point Of View ◽  
Zero Temperature ◽  
Tuning Parameters ◽  
First Order ◽  
End Point ◽  
Fundamental Point ◽  
New Type ◽  
Quantum Critical ◽  
The Magnetic Field

In this paper, we discuss the concept of a metamagnetic quantum critical end-point, consequence of the depression to zero temperature of a critical end-point terminating a line of first order first transitions. This new type of quantum critical point (QCP) is interesting both from a fundamental point of view: a study of a symmetry conserving QCP, and because it opens the possibility of the use of symmetry breaking tuning parameters, notably the magnetic field. In addition, we discuss the experimental evidence for the existence of such a QCP in the bilayer ruthenate Sr3Ru2O7.

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