scholarly journals The Effect of Fe Doping on the Magnetic and Magnetocaloric Properties of Mn5−xFexGe3

2017 ◽  
Vol 2017 ◽  
pp. 1-7 ◽  
Author(s):  
Jeffrey Brock ◽  
Nathanael Bell-Pactat ◽  
Hong Cai ◽  
Timothy Dennison ◽  
Tucker Fox ◽  
...  
Keyword(s):  
Phase Transition ◽  
Order Phase Transition ◽  
Room Temperature ◽  
Entropy Change ◽  
Second Order ◽  
Ferromagnetic Transition ◽  
Fe Doping ◽  
First Order Phase Transition ◽  
Magnetocaloric Properties ◽  
First Order Phase

The magnetic and magnetocaloric properties of a series of minutely doped Mn5-xFexGe3 compounds that exhibit the D88-type hexagonal crystal structure at room temperature have been investigated. For all Fe concentrations, the alloys are ferromagnetic and undergo a second-order ferromagnetic-to-paramagnetic transition near room temperature. Although the small Fe doping had little effect on the ferromagnetic transition temperatures of the system, changes in the saturation magnetization and magnetic anisotropy were observed. For x≤0.15, all compounds exhibit nearly the same magnetic entropy change of ~7 J/kg K, for a field change of 50 kOe. However, the magnitude of the refrigerant capacities increased with Fe doping, with values up to 108.5 J/kg and 312 J/kg being observed for field changes of 20 kOe and 50 kOe, respectively. As second-order phase transition materials, the Mn5-xFexGe3 compounds are not subject to the various drawbacks associated with first-order phase transition materials yet exhibit favorable magnetocaloric effects.

scholarly journals First- and second-order phase transitions in RE6Co2Ga (RE = Ho, Dy or Gd) cryogenic magnetocaloric materials

2021 ◽  
Author(s):  
Dan Guo ◽  
Luis M. Moreno-Ramírez ◽  
Carlos Romero-Muñiz ◽  
Yikun Zhang ◽  
Jia-Yan Law ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Order Phase Transition ◽  
Density Functional ◽  
Magnetic Ordering ◽  
Density Functional Theory Calculations ◽  
Entropy Change ◽  
Second Order ◽  
First Order Phase Transition ◽  
First Order Phase

AbstractRare-earth (RE) rich intermetallics crystallizing in orthorhombic Ho6Co2Ga-type crystal structure exhibit peculiar magnetic properties that are not widely reported for their magnetic ordering, order of magnetic phase transition, and related magnetocaloric behavior. By tuning the type of RE element in RE6Co2Ga (RE = Ho, Dy or Gd) compounds, metamagnetic anti-to-paramagnetic (AF to PM) phase transitions could be tuned to ferro-to-paramagnetic (FM to PM) phase transitions. Furthermore, the FM ground state for Gd6Co2Ga is confirmed by density functional theory calculations in addition to experimental observations. The field dependence magnetocaloric and Banerjee’s criteria demonstrate that Ho6Co2Ga and Dy6Co2Ga undergo a first-order phase transition in addition to a second-order phase transition, whereas only the latter is observed for Gd6Co2Ga. The two extreme alloys of the series, Ho6Co2Ga and Gd6Co2Ga, show maximum isothermal entropy change (∣ΔS iso max (5 T)∣) of 10.1 and 9.1 J kg−1K−1 at 26 and 75 K, close to H2 and N2 liquefaction, respectively. This outstanding magnetocaloric effect performance makes the RE6Co2Ga series of potential for cryogenic magnetic refrigeration applications.

scholarly journals 127I NQR and Crystal Structure Studies of [N(CH3)4]2 CdI4

2000 ◽  
Vol 55 (1-2) ◽  
pp. 225-229 ◽  
Author(s):  
Hideta Ishihara ◽  
Keizo Horiuchi ◽  
Thorsten M. Gesing ◽  
Shi-qi Dou ◽  
J.-Christian Buhl ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Order Phase Transition ◽  
Intensity Ratio ◽  
Room Temperature ◽  
Liquid Nitrogen Temperature ◽  
Temperature Phase ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

The temperature dependence of 127I NQR and DSC as well as the crystal structure at room temperature of the title compound were determined. This compound shows a first-order phase transition of an order-disorder type at 245 K. Eight 127I(v1:m = ±1/2 ↔ ±3/2) NQR lines of 79.57, 81.86, 82.56, 83.36, 84.68, 87.72, 88.34, and 88.86 MHz, and corresponding eight 127I(v2: m = ±3/2 ↔±5/2) NQR lines were observed at liquid nitrogen temperature. Three 127I(υi) NQR lines wfth an intensity ratio of 1:1:2 in the order of decreasing frequency were observed just above the transition point and two NQR lines except for the middle-frequency line disappeared around room temperature. This temperature behavior of NQR lines is very similar to that observed in [N(CH3)4]2Hgl4. Another first-order phase transition takes place at 527 K. The structure of the room-temperature phase was redetermined: orthorhombic, Pnma, Z = 4, a = 1342.8(3), b = 975.7(2), c = 1696.5(3) pm. The NQR result of three lines with an intensity ratio of 1:1:2 is in agreement with this structure. The thermal displacement parameters of atoms in both cations and anions are large.

scholarly journals N-Methylpyrrolidinium hydrogen tartrate (NMPHT): an above-room-temperature order–disorder molecular switchable dielectric material

RSC Advances ◽  
2017 ◽  
Vol 7 (39) ◽  
pp. 24368-24373 ◽  
Author(s):  
Aurang Zeb ◽  
Tariq Khan ◽  
Muhammad Adnan Asghar ◽  
Zhihua Sun ◽  
Zhenyue Wu ◽  
...  
Keyword(s):  
Phase Transition ◽  
Order Phase Transition ◽  
Room Temperature ◽  
Dielectric Material ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

A new above-room-temperature molecular switchable dielectric material, which undergoes a first-order phase transition induced by the order-disorder transformation of cation, has been reported.

Room-Temperature First-Order Phase Transition in a Charge-Disproportionated Molecular Conductor (MeEDO-TTF)2PF6

2008 ◽  
Vol 20 (24) ◽  
pp. 7551-7562 ◽  
Author(s):  
Xiangfeng Shao ◽  
Yoshiaki Nakano ◽  
Masafumi Sakata ◽  
Hideki Yamochi ◽  
Yukihiro Yoshida ◽  
...  
Keyword(s):  
Phase Transition ◽  
Order Phase Transition ◽  
Room Temperature ◽  
First Order ◽  
Molecular Conductor ◽  
First Order Phase Transition ◽  
A Charge ◽  
First Order Phase

scholarly journals Geometric Curvatures of Plane Symmetry Black Hole

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Shao-Wen Wei ◽  
Yu-Xiao Liu ◽  
Chun-E. Fu ◽  
Hai-Tao Li
Keyword(s):  
Phase Transition ◽  
Black Hole ◽  
Order Phase Transition ◽  
Semiclassical Approximation ◽  
Second Order ◽  
Plane Symmetry ◽  
First Order ◽  
First Order Phase Transition ◽  
Transition Points ◽  
First Order Phase

We study the properties and thermodynamic stability of the plane symmetry black hole from the viewpoint of geometry. We find that the Weinhold curvature gives the first-order phase transition atN=1, whereNis a parameter of the plane symmetry black hole while the Ruppeiner one shows first-order phase transition points for arbitraryN≠1. Considering the Legendre invariant proposed by Quevedo et al., we obtain a unified geometry metric, which contains the information of the second-order phase transition. So, the first-order and second-order phase transitions can be both reproduced from the geometry curvatures. The geometry is also found to be curved, and the scalar curvature goes to negative infinity at the Davie phase transition points beyond semiclassical approximation.

scholarly journals Specific heat and entropy change at the first order phase transition of La(Fe-Mn-Si)13-H compounds

2015 ◽  
Vol 118 (5) ◽  
pp. 053907 ◽  
Author(s):  
Vittorio Basso ◽  
Michaela Küpferling ◽  
Carmen Curcio ◽  
Cecilia Bennati ◽  
Alexander Barzca ◽  
...  
Keyword(s):  
Phase Transition ◽  
Specific Heat ◽  
Order Phase Transition ◽  
Entropy Change ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

Effect of Nd Substitution on the Structural and Magnetocaloric Properties of Gd5Si2Ge2

2015 ◽  
Vol 830-831 ◽  
pp. 501-504
Author(s):  
Bhagya Uthaman ◽  
Manoj Raama Varma
Keyword(s):  
Phase Transition ◽  
Curie Temperature ◽  
Magnetic Transition ◽  
Ferromagnetic Transition ◽  
First Order ◽  
Arc Melting ◽  
First Order Phase Transition ◽  
Magnetocaloric Properties ◽  
Nd Substitution ◽  
First Order Phase

In the present work, Nd substituted Gd5-xNdxSi2Ge2 with x = 0.05, 0.1 and 0.2 have been synthesized by arc melting and the effect of Nd substitution on the structural and magnetocaloric properties of Gd5Si2Ge2 has been investigated. The composition with x=0.05 undergoes a first order phase transition with a Curie temperature of 275 K. With the increase in Nd content to x=0.1 and x=0.2, the compounds undergo a second order magnetic transition at 300 K and 293 K respectively. Maximum entropy changes (-ΔSM) for Gd5-xNdxSi2Ge2 alloys with x = 0.05, 0.1 and 0.2 are 12.8, 7.6 and 7.2 J/kg K, respectively, for 50 kOe. The critical exponent analysis of the paramagnetic to ferromagnetic transition and the scaling behaviour of field dependence of MCE for x=0.1 and 0.2 compositions is also carried out.

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