scholarly journals Magnetocaloric Effect in Cu5-NIPA Molecular Magnet: A Theoretical Study

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 485 ◽  
Author(s):  
Karol Szałowski ◽  
Pamela Kowalewska
Keyword(s):  
Magnetic Field ◽  
Magnetocaloric Effect ◽  
Theoretical Study ◽  
Canonical Ensemble ◽  
Entropy Change ◽  
Molecular Magnet ◽  
Wide Range ◽  
Magnetocaloric Properties ◽  
Magnetic Specific Heat ◽  
High Degree

We calculated the magnetocaloric properties of the molecular nanomagnet Cu5-NIPA, consisting of five spins S = 1 / 2 arranged in two corner-sharing triangles (hourglass-like structure without magnetic frustration). The thermodynamics of the system in question was described using the quantum Heisenberg model solved within the field ensemble (canonical ensemble) using exact numerical diagonalization. The dependence of the magnetic entropy and magnetic specific heat on the temperature and the external magnetic field was investigated. The isothermal entropy change for a wide range of initial and final magnetic fields was discussed. Due to plateau-like behavior of the isothermal entropy change as a function of the temperature, a high degree of tunability of magnetocaloric effect with the initial and final magnetic field was demonstrated.

scholarly journals Магнитокалорический эффект в окрестности температуры магнитной компенсации аморфных ферримагнитных пленок Gd-Co

2021 ◽  
Vol 63 (9) ◽  
pp. 1325
Author(s):  
А.В. Свалов ◽  
А.В. Архипов ◽  
В.Н. Лепаловский ◽  
Е.А. Степанова ◽  
В.О. Васьковский ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Anisotropy ◽  
Magnetocaloric Effect ◽  
Magnetic Structure ◽  
Perpendicular Magnetic Anisotropy ◽  
Film Plane ◽  
Probable Reason ◽  
Wide Range ◽  
Magnetocaloric Properties ◽  
The Magnetic Field

The magnetic and magnetocaloric properties of amorphous ferrimagnetic Gd-Co films with perpendicular magnetic anisotropy were studied in a wide range of fields and temperatures. The change in the sign of the magnetocaloric effect near the compensation temperature occurs almost abruptly when the magnetic field is oriented perpendicular to the film plane. In a certain temperature range, it happens when the field is oriented along the plane of the sample. The most probable reason for the blurring of this transition is the appearance of a non-collinear magnetic structure.

The Effect of Plastic Deformation on Magnetic and Magnetocaloric Properties of Gd90Ga10 Alloy

2016 ◽  
Vol 845 ◽  
pp. 56-60 ◽  
Author(s):  
Sergey Taskaev ◽  
Konstantin Skokov ◽  
Dmitriy Karpenkov ◽  
Vladimir V. Khovaylo ◽  
Maxim N. Ulyanov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Heat Treatment ◽  
Plastic Deformation ◽  
Magnetocaloric Effect ◽  
Entropy Change ◽  
High Temperature Heat Treatment ◽  
Magnetocaloric Properties ◽  
Temperature Heat ◽  
Cold Rolled ◽  
Temperature Heat Treatment

In this work we report the results of experimental investigation of the magnetocaloric effect in Gd90Ga10 cold rolled ribbons. A moderate entropy change ΔS = 3.5 J/(kg·K) and magnetocaloric effect ΔT = 3.4K was observed for the as-cast materials in an external magnetic field of 2T which is less by 35% in comparison with the pure gadolinium metal. It was found that a significant (up to 70%) depression of magnetization and magnetocaloric properties developed in the course of plastic deformation can be completely restored by means of a high temperature heat treatment.

scholarly journals Low-Temperature Magnetocaloric Properties of V12 Polyoxovanadate Molecular Magnet: A Theoretical Study

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4399 ◽  
Author(s):  
Karol Szałowski
Keyword(s):  
Low Temperature ◽  
Magnetocaloric Effect ◽  
Computational Study ◽  
Thermodynamic Description ◽  
Entropy Change ◽  
Molecular Magnet ◽  
Thermodynamic Quantities ◽  
Magnetocaloric Properties ◽  
Adiabatic Magnetization ◽  
Quantities Of Interest

The paper presents a computational study of the magnetocaloric properties of the V12 polyoxovanadate molecular magnet. The description is restricted to low-temperature range (below approximately 100 K), where the magnetic properties of the system in question can be sufficiently modelled by considering a tetramer that consists of four vanadium ions with spins S=1/2. The discussion is focused on the magnetocaloric effect in the cryogenic range. The exact and numerical diagonalization of the corresponding Hamiltonian is used in order to construct the thermodynamic description within a version of the canonical ensemble. The thermodynamic quantities of interest, such as magnetic entropy, specific heat, entropy change under isothermal magnetization/demagnetization, temperature change under adiabatic magnetization/demagnetization, refrigerant capacity, and magnetic Grüneisen ratio, are calculated and discussed extensively. The importance of two quantum level crossings for the described properties is emphasized. The significant ranges of direct and inverse magnetocaloric effect are predicted. In particular, the maximized inverse magnetocaloric response is found for cryogenic temperatures.

scholarly journals Tuning Magnetocaloric Properties for La-=SUB=-1-x-=/SUB=-Sr-=SUB=-x-=/SUB=-CoO-=SUB=-3-=/SUB=-

2021 ◽  
Vol 63 (10) ◽  
pp. 1551
Author(s):  
E.M. Ahmed ◽  
H.R. Alamri ◽  
S.M. Elghnam ◽  
O. Eldarawi ◽  
T.E. Tawfik ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
Magnetocaloric Effect ◽  
Magnetic Entropy Change ◽  
Entropy Change ◽  
Paramagnetic State ◽  
Magnetic Entropy ◽  
Magnetocaloric Properties ◽  
Low Magnetic Field

Low magnetic field magnetocaloric (MC) properties of La1-xSrxCoO3 (x=0.3 and 0.5) near phase transition from a ferromagnetic to a paramagnetic state were investigated. It is shown that the change of Sr content allows MC effect in La1-xSrxCoO3 to be tunable, which is more practical for construction of MC refrigeration. MC properties of the x=0.5 sample are significantly greater than that of the x=0.3 one. Furthermore, the results show that MC properties of La1-xSrxCoO3 samples are significantly larger, and comparable with some MC properties of many materials like Gd1-xCaxBaCo2O5.5 and Ge0.95Mn0.05. Keywords: magnetocaloric effect, La1-xSrxCoO3, magnetic entropy change.

Magnetocaloric Effect in Ho-Er-Gd-Co Multicomponent Compounds

2012 ◽  
Vol 190 ◽  
pp. 303-306
Author(s):  
J. Ćwik ◽  
T. Palewski ◽  
K. Nenkov ◽  
J. Lyubina ◽  
Oliver Gutfleisch
Keyword(s):  
Magnetic Field ◽  
Magnetocaloric Effect ◽  
Solid Solutions ◽  
Entropy Change ◽  
Step Motor ◽  
X Ray Diffraction ◽  
Magnetocaloric Properties ◽  
Diffraction Patterns ◽  
Heat Capacity Measurements ◽  
Type Magnet

We report magnetic and magnetocaloric properties of polycrystalline series of the (Ho0.9Er0.1)1-xGdxCo2(x = 0.05, 0.1 and 0.15) solid solutions. These samples were synthesized using high purity rare earth metals and cobalt. X-ray diffraction patterns taken at room temperature reveal that all compounds have the C15 cubic Laves phase structure. Magnetization measurements were carried out using a vibration sample magnetometer with a step motor in fields up to 14 T using a Bitter-type magnet. Heat capacity measurements have been performed in the temperature range of 2-300 K without magnetic field and in a magnetic field of 1 and 2 T. The magnetocaloric effect has been estimated in terms of isothermal magnetic entropy change for all solid solutions in magnetic fields up to 3 T. The effect of increasing Gd amount in (Ho0.9Er0.1)1-xGdxCo2on the magnetic and magnetocaloric properties will be discussed.

scholarly journals Magnetocaloric properties of La0.666Sr0.373Mn0.943Cu0.018O3

2017 ◽  
Vol 11 (3) ◽  
pp. 225-228 ◽  
Author(s):  
Mahmoud Hamad
Keyword(s):  
Magnetocaloric Effect ◽  
Magnetic Entropy Change ◽  
Entropy Change ◽  
Cooling Power ◽  
Magnetic Entropy ◽  
Active Magnetic Regenerator ◽  
Magnetocaloric Properties ◽  
Magnetic Specific Heat ◽  
Prospective Application ◽  
Magnetic Regenerator

Magnetocaloric properties of La0.666Sr0.373Mn0.943Cu0.018O3 (LSMCO) perovskite (such as magnetic entropy change, full-width at half-maximum, relative cooling power and magnetic specific heat change) at applied magnetic field of 0.05 T were calculated using the phenomenological model. The results indicate the prospective application of LSMCO due to high magnetocaloric effect near the Curie temperature. Furthermore, the magnetocaloric properties of LSMCO sample are comparable with magnetocaloric properties of MnAs film, La1-xCdxMnO3 and La1.25Sr0.75MnCoO6, and significantly larger than that of Gd1-xCaxBaCo2O5.5 and Ge0.95Mn0.05. It is recommended that magnetocaloric effect of LSMCO can be used as a promising practical material of an apparatus based on the active magnetic regenerator cycle.

scholarly journals Magnetic Properties and Magnetocaloric Effect in Gd100-xCox Thin Films

Crystals ◽  
2019 ◽  
Vol 9 (6) ◽  
pp. 278 ◽  
Author(s):  
Mohamed Tadout ◽  
Charles-Henri Lambert ◽  
Mohammed El Hadri ◽  
Abdelilah Benyoussef ◽  
Mohammed Hamedoun ◽  
...  
Keyword(s):  
Thin Films ◽  
Magnetocaloric Effect ◽  
Magnetic Entropy Change ◽  
Entropy Change ◽  
Magnetic Thin Films ◽  
Critical Parameters ◽  
Cooling Power ◽  
Magnetocaloric Properties ◽  
Co Concentration ◽  
Key Parameter

We investigated the magnetic and magnetocaloric properties of Gd100-xCox ( x = 40 to 56) thin films fabricated by the sputtering technique. Under an applied field change Δ H = 20 kOe , the magnetic entropy change ( Δ S m ) decreases from 2.64 Jkg−1K−1 for x = 44 to about 1.27 Jkg−1K−1 for x = 56. Increasing the Co concentration from x = 40 to 56 shifts the Curie temperature of Gd100-xCox ( x = 40 to 56) thin films from 180 K toward 337 K. Moreover, we extracted the values of critical parameters Tc, β, γ, and δ by using the modified Arrott plot methods. The results indicate the presence of a long-range ferromagnetic order. More importantly, we showed that the relative cooling power (RCP), which is a key parameter in magnetic refrigeration applications, is strongly enhanced by changing the Co concentration in the Gd100-xCox thin films. Our findings help pave the way toward the enhancement of the magnetocaloric effect in magnetic thin films.

Magnetic Properties and Magnetocaloric Effect of Gd3Ni in Crystalline and Amorphous States

2012 ◽  
Vol 190 ◽  
pp. 355-358 ◽  
Author(s):  
D.A. Shishkin ◽  
N.V. Baranov ◽  
A.V. Proshkin ◽  
S.V. Andreev ◽  
A.S. Volegov
Keyword(s):  
Magnetic Field ◽  
Magnetocaloric Effect ◽  
Entropy Change ◽  
Rapid Quenching ◽  
Antiferromagnetic Order ◽  
Cooling Power ◽  
Ferromagnetic Behavior ◽  
Field Change ◽  
Ni Alloy ◽  
Magnetic Field Change

The liquid quenched Gd3Ni alloy is observed to exhibit a ferromagnetic behavior below TC = 117 K unlike crystalline compound having an antiferromagnetic order at T < TN = 99 K. Rapid quenching from the melt results in a considerable enhancement of the magnetocaloric effect in Gd3Ni at low magnetic fields. The maximal value of the isothermal magnetic entropy change at a magnetic field change of 20 kOe for the amorphous Gd3Ni surpasses by more than 8 times the SM value for the polycrystalline counterpart. The relative cooling power for the amorphous Gd3Ni alloy is estimated as 265 J kg-1 and 676 J kg-1 at a magnetic field change of 20 kOe and 50 kOe, respectively.

scholarly journals Weak Singularities of the Isothermal Entropy Change as the Smoking Gun Evidence of Phase Transitions of Mixed-Spin Ising Model on a Decorated Square Lattice in Transverse Field

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1533
Author(s):  
Jozef Strečka ◽  
Katarína Karl’ová
Keyword(s):  
Magnetic Field ◽  
Phase Transitions ◽  
Ising Model ◽  
Magnetocaloric Effect ◽  
Entropy Change ◽  
Transverse Magnetic ◽  
Continuous Phase ◽  
Square Lattice ◽  
Mixed Spin ◽  
Weak Singularities

The magnetocaloric response of the mixed spin-1/2 and spin-S (S>1/2) Ising model on a decorated square lattice is thoroughly examined in presence of the transverse magnetic field within the generalized decoration-iteration transformation, which provides an exact mapping relation with an effective spin-1/2 Ising model on a square lattice in a zero magnetic field. Temperature dependencies of the entropy and isothermal entropy change exhibit an outstanding singular behavior in a close neighborhood of temperature-driven continuous phase transitions, which can be additionally tuned by the applied transverse magnetic field. While temperature variations of the entropy display in proximity of the critical temperature Tc a striking energy-type singularity (T−Tc)log|T−Tc|, two analogous weak singularities can be encountered in the temperature dependence of the isothermal entropy change. The basic magnetocaloric measurement of the isothermal entropy change may accordingly afford the smoking gun evidence of continuous phase transitions. It is shown that the investigated model predominantly displays the conventional magnetocaloric effect with exception of a small range of moderate temperatures, which contrarily promotes the inverse magnetocaloric effect. It turns out that the temperature range inherent to the inverse magnetocaloric effect is gradually suppressed upon increasing of the spin magnitude S.

Thermomagnetic Properties and Magnetocaloric Effect of R2Fe17C (R=Dy, Nd, Tb, Gd, Pr, Ho, Er) Compounds

2018 ◽  
Vol 1 (1) ◽  
pp. 268-278
Author(s):  
Ahmed Nagy ◽  
Samy H. Aly ◽  
Sherif Yehia ◽  
Tareq Hammad
Keyword(s):  
Magnetocaloric Effect ◽  
Mean Field ◽  
Entropy Change ◽  
Field Analysis ◽  
Magnetic Phase Transitions ◽  
Mean Field Model ◽  
Magnetocaloric Properties ◽  
The Mean ◽  
Thermomagnetic Properties ◽  
Critical Temperature Tc

We present a mean-field analysis, using the two-sublattice model, for the thermomagnetic and magnetocaloric properties of the R2Fe17C compounds, where R=Dy, Nd, Tb, Gd, Pr, Ho, Er and C is carbon.   The dependence of magnetization, magnetic heat capacity, magnetic entropy and isothermal entropy change ∆Sm, are calculated for magnetic fields up to 5T and for temperatures up to 700 K . Direct magnetocaloric effect is present for all compounds with maximum ∆Sm between 6.13-10.95 J/K. mole for an applied field change of 5T. It is found that Pr2Fe17C compound has the highest  ∆Sm of 10.95 J/K. mole at ∆H=5T and Tc=375 K. The inverse MCE is found in ferrimagnetic compounds, e.g. Gd2Fe17C, with ∆Sm= J/K mol at critical temperature Tc=623K and ∆Sm=  J/K mol at Neel temperature TN=136 K.  The calculated Arrott plots confirmed that the magnetic phase transitions in these compounds are of second order. The mean-field model proves its suitability for calculating the properties of the compounds under study.

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