scholarly journals Magnetic properties of CrFeCoNi based high entory alloy

2021 ◽  
Vol 2122 (1) ◽  
pp. 012004
Author(s):  
Junqi Yin ◽  
Markus Eisenbach ◽  
Makrus Daene ◽  
G. Malcolm Stocks
Keyword(s):  
Transition Temperature ◽  
Magnetic Order ◽  
Magnetic Phase ◽  
Finite Size ◽  
Exchange Interactions ◽  
Universality Class ◽  
Potential Approximation ◽  
High Entropy ◽  
Scaling Analyses ◽  
The Individual

Abstract Monte Carlo simulations are performed on three high entropy alloys: Cr0.25Fe0.25Co0.25Ni0.25, Cr0.2Fe0.2Co0.2Ni0.2Pd0.2, and Cr0.2Mn0.2Fe0.2Co0.2Ni0.2, with exchange interactions extracted from The ab initio Korringa-Kohn-Rostoker method combined with the coherent potential approximation calculations. Using finite size scaling analyses, we estimate the magnetic phase transition temperature for the four component alloy to be 108(2) K, and although the individual critical exponents are different from 3D Heisenberg universality class, the reduced exponent follows Suzuki weak universality. With the additional Palladium component, the transition temperature elevates to about 200 K. In contrast, we find no magnetic order for the five component alloy with Manganese at any finite temperatures.

Magnetic Phase Transitions and Magnetocaloric Effect in R2Fe17 (R = Y, Tb, Er)

2015 ◽  
Vol 233-234 ◽  
pp. 204-207 ◽  
Author(s):  
S.A. Nikitin ◽  
I.A. Ovchenkova ◽  
Georgiy A. Tskhadadze ◽  
Konstantin P. Skokov
Keyword(s):  
Transition Temperature ◽  
Magnetocaloric Effect ◽  
Magnetic Phase ◽  
Magnetic Transition ◽  
Exchange Interactions ◽  
Thermodynamic Theory ◽  
Magnetic Phase Transitions ◽  
Magnetic Transition Temperature ◽  
Local Fluctuations ◽  
Direct Measurements

The direct measurements of the magnetocaloric effect (MCE) and the magnetization for R2Fe17 (R = Y, Tb, Dy) compounds are reported. The maximal values of the MCE for different R2Fe17 compounds are almost the same at the Curie temperature and are equal to 0.8 – 0.85 K at ΛH = 13.5 kOe. The field dependencies of the magnetization and MCE and the dependence of MCE via magnetization deviates from the classical regularities and describes by the thermodynamic theory attracting the higher terms. Obviously the occurrence of the mixed exchange interactions in these compounds leads to the requirement of consideration both thermal and local fluctuations of the exchange integrals near the magnetic transition temperature.

scholarly journals Universality and Exact Finite-Size Corrections for Spanning Trees on Cobweb and Fan Networks

Entropy ◽  
2019 ◽  
Vol 21 (9) ◽  
pp. 895
Author(s):  
Nickolay Izmailian ◽  
Ralph Kenna
Keyword(s):  
Generating Functions ◽  
Spanning Trees ◽  
Central Charge ◽  
Finite Size ◽  
Universality Class ◽  
Partition Functions ◽  
Free Energies ◽  
Conformal Theory ◽  
Alternative Means ◽  
The Individual

The concept of universality is a cornerstone of theories of critical phenomena. It is very well understood in most systems, especially in the thermodynamic limit. Finite-size systems present additional challenges. Even in low dimensions, universality of the edge and corner contributions to free energies and response functions is less investigated and less well understood. In particular, the question arises of how universality is maintained in correction-to-scaling in systems of the same universality class but with very different corner geometries. Two-dimensional geometries deliver the simplest such examples that can be constructed with and without corners. To investigate how the presence and absence of corners manifest universality, we analyze the spanning tree generating function on two different finite systems, namely the cobweb and fan networks. The corner free energies of these configurations have stimulated significant interest precisely because of expectations regarding their universal properties and we address how this can be delivered given that the finite-size cobweb has no corners while the fan has four. To answer, we appeal to the Ivashkevich–Izmailian–Hu approach which unifies the generating functions of distinct networks in terms of a single partition function with twisted boundary conditions. This unified approach shows that the contributions to the individual corner free energies of the fan network sum to zero so that it precisely matches that of the web. It therefore also matches conformal theory (in which the central charge is found to be c = − 2 ) and finite-size scaling predictions. Correspondence in each case with results established by alternative means for both networks verifies the soundness of the Ivashkevich–Izmailian–Hu algorithm. Its broad range of usefulness is demonstrated by its application to hitherto unsolved problems—namely the exact asymptotic expansions of the logarithms of the generating functions and the conformal partition functions for fan and cobweb geometries. We also investigate strip geometries, again confirming the predictions of conformal field theory. Thus, the resolution of a universality puzzle demonstrates the power of the algorithm and opens up new applications in the future.

scholarly journals Критические свойства в модели Изинга на треугольной решетке с переменным межслойным обменным взаимодействием

2019 ◽  
Vol 61 (10) ◽  
pp. 1898
Author(s):  
А.К. Муртазаев ◽  
М.К. Рамазанов ◽  
М.К. Бадиев
Keyword(s):  
Order Parameter ◽  
Finite Size ◽  
Exchange Interactions ◽  
Universality Class ◽  
Correlation Radius ◽  
Ising Models ◽  
Finite Size Scaling ◽  
Antiferromagnetic Ising Model ◽  
Interlayer Exchange ◽  
Range Of Values

The Monte Carlo replica algorithm studies of phase transitions and critical phenomenaofthe layered triangular antiferromagnetic Ising model withvariable interlayer exchange interaction. Investigations were carried out for the ratios of the value of the intralayerJ1 and interlayer J2 exchange interactions in the range of values r = J2 / J1 = 0.01 ÷ 1.0. It was found that in the above range r is observed second-order phase transition.Static critical exponents for the heat capacityα, susceptibility γ, order parameter β, correlation radius ν, and the Fisher exponent ηare computed by means of the finite-size scaling theory. It is shown that the universality class of the critical behavior of the model is maintained in the range of 0.05 <r≤1.0.The results obtained suggest that3D frustrated Ising models on stacked triangularlattice with interlayer-to-intralayer exchange ratio 0.05<r≤1.0. preserves the universality class of criticalbehavior. At lower r, a crossover from 3D to 2D criticalbehavior is observed.

Anomalies of Elastic Properties at Phase Transitions in Rare Earth Cobaltites RBaCo4O7 (R = Y, Er - Lu)

2012 ◽  
Vol 190 ◽  
pp. 482-485 ◽  
Author(s):  
Z.A. Kazei ◽  
V.V. Snegirev ◽  
L.P. Kozeeva ◽  
M.Yu. Kameneva
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Rare Earth ◽  
Transition Temperature ◽  
Elastic Properties ◽  
Magnetic Phase ◽  
Structural Phase ◽  
Exchange Interactions ◽  
Temperature Decrease ◽  
Low Dimension

Elastic properties of rare-earth cobaltites RBaCo4O7 (R = Y, Er - Lu) are studied in the temperature range (4.2 - 300) K. Significant softening of Youngs modulus for Lu-and Yb-cobaltites is found at temperature decrease, showing an instability of the crystal structure and accompanying by a reverse jump at the structural phase transition. Softening and jump at phase transition decrease more than by the order of value, while the transition temperature Ts and hysteresis dTs enlarge from Lu-to Tm-and Er-compounds. Smooth and weak elastic anomaly at the magnetic phase transition is found resulting from low dimension and frustration of exchange interactions in the Co subsystem in most of the rare-earth cobaltites studied.

Effect of pressure on magnetic phase transitions of europium chalcogenides: EuO, EuS, and EuSe

1968 ◽  
Vol 46 (23) ◽  
pp. 2703-2713 ◽  
Author(s):  
V. C. Srivastava ◽  
R. Stevenson
Keyword(s):  
Transition Temperature ◽  
Magnetic Phase ◽  
Exchange Interactions ◽  
Theoretical Models ◽  
Lattice Parameter ◽  
Magnetic Phase Transitions ◽  
Magnetic Exchange ◽  
Effect Of Pressure ◽  
Volume Dependence ◽  
Magnetic Specific Heat

The effect of pressure on magnetic transitions of EuS and EuSe is reported up to 10 kbars. The compressibilities of EuO, EuS, and EuSe have been measured at 4.2, 82, and 300 °K for the same pressure range. The shift in the transition temperature of these materials has been measured through the mutual inductance of an astatic coil assembly containing the sample. Values of dTc/dP = +0.20 × 10−3 °K/bar for EuS and of dTN/dP = +0.16 × 10−3 °K/bar for EuSe have been obtained. Combining the compressibility measurements with dTc−N/dP the values of dTc−N/da = −290, −102, −68 °K/Å are obtained for EuO, EuS, and EuSe respectively, where a is the lattice parameter. These values of dTc/da for EuO and EuS are about three and two times the values derived from the plot of paramagnetic Curie temperature versus lattice parameter given by McGuire and Shafer. This difference is thought to be due to variations in covalency in going from oxide to selenide. For EuSe the value of dTN/da is in rough agreement with the value obtained by McGuire and Shafer. It is observed that volume dependence of magnetic exchange interactions in these solids deviates strongly from that of common superexchange materials; the magnetic Grüneisen constant is measured to be[Formula: see text]for EuO, EuS, and EuSe respectively. On the basis of recent theoretical models proposed for these materials, it is suggested that for EuS and EuSe the magnetic expansivity αmc should be proportional to the magnetic specific heat cm near the transition temperature according to the relation dTc/dP = 3TcVαmc/cm. The ratio αme/cm is estimated from the present measurements.

Instant and Persistent Hydrogen Production Using Nano High Entropy Catalyst

2019 ◽  
Author(s):  
Nirmal Kumar ◽  
Subramanian Nellaiappan ◽  
Ritesh Kumar ◽  
Kirtiman Deo Malviya ◽  
K. G. Pradeep ◽  
...  
Keyword(s):  
Formic Acid ◽  
Minimum Energy ◽  
High Entropy Alloy ◽  
Hydrogen Energy ◽  
High Entropy ◽  
Electro Oxidation ◽  
The Individual ◽  
Novel Catalyst ◽  
Cell Anode ◽  
Fuel Cell Anode

<div>Renewable harvesting clean and hydrogen energy using the benefits of novel multicatalytic materials of high entropy alloy (HEA equimolar Cu-Ag-Au-Pt-Pd) from formic acid with minimum energy input has been achieved in the present investigation. The synthesis effect of pristine elements in the HEA drives the electro-oxidation reaction towards non-carbonaceous pathway . The atomistic simulation based on DFT rationalize the distinct lowering of the d-band center for the individual atoms in the HEA as compared to the pristine counterparts. This catalytic activity of the HEA has also been extended to methanol electro-oxidation to show the unique capability of the novel catalyst. The nanostructured HEA, properties using a combination of casting and cry omilling techniques can further be utilized as fuel cell anode in direct formic acid/methanol fuel cells (DFFE).<br></div>

scholarly journals Study of physical properties of a ferrimagnetic spinel Cu1.5Mn1.5O4: spin dynamics, magnetocaloric effect and critical behavior

RSC Advances ◽  
2021 ◽  
Vol 11 (41) ◽  
pp. 25664-25676
Author(s):  
Abir Hadded ◽  
Jalel Massoudi ◽  
Sirine Gharbi ◽  
Essebti Dhahri ◽  
A. Tozri ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Physical Properties ◽  
Magnetocaloric Effect ◽  
Phase Transition Temperature ◽  
Magnetic Phase Transition ◽  
Critical Behavior ◽  
Magnetic Phase ◽  
Spin Dynamics ◽  
Critical Behaviour

The present work reports a detailed study of the spin dynamics, magnetocaloric effect and critical behaviour near the magnetic phase transition temperature, of a ferrimagnetic spinel Cu1.5Mn1.5O4.

scholarly journals Probing resonating valence bond states in artificial quantum magnets

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kai Yang ◽  
Soo-Hyon Phark ◽  
Yujeong Bae ◽  
Taner Esat ◽  
Philip Willke ◽  
...  
Keyword(s):  
Quantum Information Processing ◽  
Energy Levels ◽  
Finite Size ◽  
Valence Bond ◽  
Exchange Interactions ◽  
Atomic Scale ◽  
Scanning Tunneling ◽  
Many Body ◽  
Quantum Magnets ◽  
Resonating Valence Bond

AbstractDesigning and characterizing the many-body behaviors of quantum materials represents a prominent challenge for understanding strongly correlated physics and quantum information processing. We constructed artificial quantum magnets on a surface by using spin-1/2 atoms in a scanning tunneling microscope (STM). These coupled spins feature strong quantum fluctuations due to antiferromagnetic exchange interactions between neighboring atoms. To characterize the resulting collective magnetic states and their energy levels, we performed electron spin resonance on individual atoms within each quantum magnet. This gives atomic-scale access to properties of the exotic quantum many-body states, such as a finite-size realization of a resonating valence bond state. The tunable atomic-scale magnetic field from the STM tip allows us to further characterize and engineer the quantum states. These results open a new avenue to designing and exploring quantum magnets at the atomic scale for applications in spintronics and quantum simulations.

Magnetic Phase Transitions in the Two-Dimensional Random Mixture K2CuxCo1-xF4with Competing Exchange Interactions

1990 ◽  
Vol 59 (5) ◽  
pp. 1792-1800 ◽  
Author(s):  
Masayuki Itoh ◽  
Isao Yamada ◽  
Mamoru Ishizuka ◽  
Kiichi Amaya ◽  
Tatsuo Kobayashi ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Magnetic Phase ◽  
Exchange Interactions ◽  
Magnetic Phase Transitions ◽  
Two Dimensional ◽  
Random Mixture

scholarly journals Macroscopic degeneracy and order in the 3D plaquette Ising model

2015 ◽  
Vol 29 (20) ◽  
pp. 1550109 ◽  
Author(s):  
Desmond A. Johnston ◽  
Marco Mueller ◽  
Wolfhard Janke
Keyword(s):  
Low Temperature ◽  
Magnetic Order ◽  
Finite Size ◽  
Temperature Phase ◽  
Finite Size Scaling ◽  
First Order ◽  
Magnetic Order Parameter ◽  
First Order Transition ◽  
Definition Of ◽  
Low Temperature Phase

The purely plaquette 3D Ising Hamiltonian with the spins living at the vertices of a cubic lattice displays several interesting features. The symmetries of the model lead to a macroscopic degeneracy of the low-temperature phase and prevent the definition of a standard magnetic order parameter. Consideration of the strongly anisotropic limit of the model suggests that a layered, “fuki-nuke” order still exists and we confirm this with multi-canonical simulations. The macroscopic degeneracy of the low-temperature phase also changes the finite-size scaling corrections at the first-order transition in the model and we see this must be taken into account when analyzing our measurements.

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