scholarly journals Magnetism and Thermomechanical Properties in Si Substituted MnCoGe Compounds

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 694
Author(s):  
Abdul Rashid Abdul Rahman ◽  
Muhamad Faiz Md Din ◽  
Jianli Wang ◽  
Nur Sabrina Suhaimi ◽  
Nurul Hayati Idris ◽  
...  
Keyword(s):  
Magnetocaloric Effect ◽  
Structural Transition ◽  
Thermal Hysteresis ◽  
Landau Theory ◽  
Magnetic Measurement ◽  
Lattice Parameter ◽  
Thermomechanical Properties ◽  
Order Type ◽  
Second Order ◽  
Dsc Measurements

MnCoGe-based compounds have been increasingly studied due to their possible large magnetocaloric effect correlated to the magnetostructural coupling. In this research, a comprehensive study of structure, magnetic phase transition, magnetocaloric effect and thermomechanical properties for MnCoGe1−xSix is reported. Room temperature X-ray diffraction indicates that the MnCoGe1−xSix (x = 0, 0.05, 0.1, 0.15 and 0.2) alloys have a major phase consisting of an orthorhombic TiNiSi-type structure with increasing lattice parameter b and decreasing others (a and c) with increasing Si concentration. Along with M-T and DSC measurements, it is indicated that the Tc value increased with higher Si concentration and decreased for structural transition temperature Tstr. The temperature dependence of the magnetization curves overlaps completely, indicating that there is no thermal hysteresis, and it is shown that the transition is the second-order type. It is also shown that the decreased magnetization on the replacement of Si for Ge decreases the value of −ΔSM from −ΔSM~8.36 J kg−1 K−1 at x = 0 to −ΔSM~5.49 J kg−1 K−1 at x = 0.2 with 5 T applied field. The performed Landau theory has confirmed the second-order transition in this study, which is consistent with the Banerjee criterion. The magnetic measurement and thermomechanical properties revealed the structural transition that takes place with Si substitution of Ge.

Structural and magnetic properties on F-doped LiVO2 with two-dimensional triangular lattice

2011 ◽  
Vol 1344 ◽  
Author(s):  
Yang Li ◽  
Xiaoxiang Li ◽  
Lihua Liu ◽  
Ning Chen ◽  
Jose García ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Thermal Hysteresis ◽  
Magnetic Ordering ◽  
Lattice Parameter ◽  
Two Dimensional ◽  
Scanning Calorimetry ◽  
Heat Measurement ◽  
Dsc Measurements ◽  
First Order Phase Transition

ABSTRACTThe layered oxide LiVO2 recently has received more attention due to its interesting structural and magnetic behaviors involving the two-dimensional magnetic frustration in these systems. We synthesized a series of F-doped LiVO2 samples, and reported the F-doping effect on the structure and transition temperature Tt. The samples LiVO2-xFx (x=0, 0.1, 0.2 and 0.3) were characterized by X-ray diffraction, scanning electron microscope (SEM), differential scanning calorimetry (DSC), magnetic susceptibility and specific heat measurement. The structural analysis shows that with increasing x, the ratio of lattice parameter c/a increasing, i.e. in the a-b plane the lattice is compressed while in the c-axis direction the lattice expands. The DSC measurements show that a first-order phase transition happens at around 500 K, and the thermal hysteresis around phase transition temperature Tt increases with increasing x. Substitution of O with F ions results in a change of two dimensional characteristics and the distortion of the VO6 block in structure, which significantly influence the magnetic ordering transition temperature Tt.

scholarly journals Effect of changing P/Ge and Mn/Fe ratios on the magnetocaloric effect and structural transition in the (Mn,Fe)2 (P,Ge) intermetallic compounds

2016 ◽  
Vol 34 (3) ◽  
pp. 494-502 ◽  
Author(s):  
P. Wlodarczyk ◽  
L. Hawelek ◽  
P. Zackiewicz ◽  
M. Kaminska ◽  
A. Chrobak ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Curie Temperature ◽  
Magnetocaloric Effect ◽  
Intermetallic Compounds ◽  
Structural Transition ◽  
Thermal Hysteresis ◽  
Simultaneous Increase ◽  
Low Field ◽  
Transition Enthalpy ◽  
Low Magnetic Field

AbstractThe magnetocaloric effect in the MnxFe2−xP1−yGey intermetallic compounds with the amount of Mn in the range of x = 1.05 to 1.17 and amount of Ge in the range of y = 0.19 to 0.22 has been studied. It was found that a higher Ge/P ratio causes an increase in Curie temperature, magnetocaloric effect at low field (up to 1 T), activation energy of structural transition and a decrease in thermal hysteresis, as well as transition enthalpy. Contrary to this observation, higher Mn/Fe ratio causes a decrease in Curie temperature, slight decrease of magnetocaloric effect at low magnetic field, and an increase in thermal hysteresis. Simultaneous increase of both ratios may be very advantageous, as the thermal hysteresis can be lowered and magnetocaloric effect can be enhanced without changing the Curie temperature. Some hints about optimization of the composition for applications at low magnetic fields (0.5 T to 2 T) have been presented.

scholarly journals Large Low-Field Reversible Magnetocaloric Effect in Itinerant-Electron Hf1-xTaxFe2 Alloys

Materials ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5233
Author(s):  
Zhao Song ◽  
Zongbin Li ◽  
Bo Yang ◽  
Haile Yan ◽  
Claude Esling ◽  
...  
Keyword(s):  
Magnetocaloric Effect ◽  
High Performance ◽  
Thermal Hysteresis ◽  
Second Order ◽  
Order Transition ◽  
Itinerant Electron ◽  
First Order ◽  
Second Order Transition ◽  
Magnetic Field Change ◽  
Materials Used

First-order isostructural magnetoelastic transition with large magnetization difference and controllable thermal hysteresis are highly desirable in the development of high-performance magnetocaloric materials used for energy-efficient and environmental-friendly magnetic refrigeration. Here, we demonstrate large magnetocaloric effect covering the temperature range from 325 K to 245 K in Laves phase Hf1-xTaxFe2 (x = 0.13, 0.14, 0.15, 0.16) alloys undergoing the magnetoelastic transition from antiferromagnetic (AFM) state to ferromagnetic (FM) state on decreasing the temperature. It is shown that with the increase of Ta content, the nature of AFM to FM transition is gradually changed from second-order to first-order. Based on the direct measurements, large reversible adiabatic temperature change (ΔTad) values of 2.7 K and 3.4 K have been achieved under a low magnetic field change of 1.5 T in the Hf0.85Ta0.15Fe2 and Hf0.84Ta0.16Fe2 alloys with the first-order magnetoelastic transition, respectively. Such remarkable magnetocaloric response is attributed to the rather low thermal hysteresis upon the transition as these two alloys are close to intermediate composition point of second-order transition converting to first-order transition.

scholarly journals Calculating the magnetocaloric effect in second-order-type material by micromagnetic simulations: A case study on Co2B

2020 ◽  
Vol 177 ◽  
pp. 218-222
Author(s):  
Dominik Ohmer ◽  
Min Yi ◽  
Maximilian Fries ◽  
Oliver Gutfleisch ◽  
Bai-Xiang Xu
Keyword(s):  
Magnetocaloric Effect ◽  
Order Type ◽  
Second Order ◽  
Type Material ◽  
Micromagnetic Simulations

PLATELET AGGREGATION DOES NOT CONFORM TO SIMPLE PARTICLE COLLISION THEORY

1987 ◽  
Author(s):  
Moideen P Jamaluddin
Keyword(s):  
Platelet Aggregation ◽  
Rate Equation ◽  
Rate Constants ◽  
Kinetic Scheme ◽  
Order Type ◽  
Second Order ◽  
Particle Collision ◽  
Collision Theory ◽  
Rate Law ◽  
First Order

Platelet aggregation kinetics, according to the particle collision theory, generally assumed to apply, ought to conform to a second order type of rate law. But published data on the time-course of ADP-induced single platelet recruitment into aggregates were found not to do so and to lead to abnormal second order rate constants much larger than even their theoretical upper bounds. The data were, instead, found to fit a first order type of rate law rather well with rate constants in the range of 0.04 - 0.27 s-1. These results were confirmed in our laboratory employing gelfiltered calf platelets. Thus a mechanism much more complex than hithertofore recognized, is operative. The following kinetic scheme was formulated on the basis of information gleaned from the literature.where P is the nonaggregable, discoid platelet, A the agonist, P* an aggregable platelet form with membranous protrusions, and P** another aggregable platelet form with pseudopods. Taking into account the relative magnitudes of the k*s and assuming aggregation to be driven by hydrophobic interaction between complementary surfaces of P* and P** species, a rate equation was derived for aggregation. The kinetic scheme and the rate equation could account for the apparent first order rate law and other empirical observations in the literature.

Landau theory of second-order phase transitions in ferroelectric films

2001 ◽  
Vol 63 (14) ◽  
Author(s):  
Lye-Hock Ong ◽  
Junaidah Osman ◽  
D. R. Tilley
Keyword(s):  
Phase Transitions ◽  
Landau Theory ◽  
Second Order ◽  
Ferroelectric Films
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