1.5.5.3.2.2 Mean field description of magnetic phase transition and Landau form of the free energy

2005 ◽  
pp. 96-103
Author(s):  
K. R. A. ZIEBECK ◽  
K.-U. NEUMANN
Keyword(s):  
Phase Transition ◽  
Free Energy ◽  
Magnetic Phase Transition ◽  
Magnetic Phase ◽  
Mean Field

scholarly journals Magnetic Phase Transition, Elastic and Thermodynamic Properties of L12-(Ni,Cu)3(Al,Fe,Cr) in 3d High-Entropy Alloys

Crystals ◽  
2020 ◽  
Vol 10 (12) ◽  
pp. 1102
Author(s):  
Li Ma ◽  
Zhi-Peng Wang ◽  
Guo-Hua Huang ◽  
Jin-Li Huang ◽  
Ping-Ying Tang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Free Energy ◽  
Gibbs Free Energy ◽  
Magnetic Phase Transition ◽  
Magnetic Phase ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Structure Phase ◽  
Temperature Dependences ◽  
Significant Temperature

The phase stability and elastic properties of paramagnetic (PM), ferromagnetic (FM) and antiferromagnetic (AFM) phases in L12-(Ni,Cu)3(Al,Fe,Cr) alloy are first investigated using the exact muffin-tin orbitals (EMTO) method in combination with the coherent potential approximation (CPA). The result shows the AFM structure phase of the three is the most stable in the ground state. Calculated elastic constants show that all the phases are mechanically stable, and have uncovered that L12-(Ni,Cu)3(Al,Fe,Cr) can achieve good strength and ductility simultaneously. Then, crucial thermal properties are described satisfactorily using the Debye–Grüneisen model, showing heat capacity, Gibbs free energy G, the competitive contribution of entropy −TS and enthalpy H exhibiting significant temperature dependences. Moreover, the magnetic phase transition thermodynamics was studied, which suggests that −TS has a primary contribution to Gibbs free energy and may play a key role in the phase transition. The present results can benefit the understanding of the mechanical, thermodynamic and magnetic properties of the L12 structure phase in 3d high-entropy alloys.

scholarly journals Investigation of magnetic phase transition and magnetocaloric effect of (Ni,Co)-Mn-Al melt-spun ribbons

2018 ◽  
Vol 185 ◽  
pp. 05001
Author(s):  
Yen Nguyen ◽  
Mai Nguyen ◽  
Quang Vu ◽  
Thanh Pham ◽  
Victor Koledov ◽  
...  
Keyword(s):  
Phase Transition ◽  
Magnetocaloric Effect ◽  
Magnetic Phase Transition ◽  
Magnetic Phase ◽  
Mean Field ◽  
Entropy Change ◽  
Soft Magnetic Materials ◽  
Critical Parameters ◽  
Mean Field Model ◽  
Diffraction Patterns

Magnetic phase transition, magnetocaloric effect and critical parameters of Ni50-xCoxMn50-yAly (x = 5 and 10; y = 17, 18 and 19) rapidly quenched ribbons have been studied. X-ray diffraction patterns exhibit a coexistence of the L21 and 10M crystalline phases of the ribbons. Magnetization measurements show that all the samples behave as soft magnetic materials with a low coercive force less than 60 Oe. The shape of thermomagnetization curves considerably depends on Co and Al concentrations. The Curie temperature (TC) of the alloy ribbons strongly increases with increasing the Co concentration and slightly decreases with increasing the Al concentration. The Ni45Co5Mn31Al19 and Ni40Co10Mn33Al17 ribbons reveal both the positive and negative magnetocaloric effects. Under magnetic field change (ΔGH) of 13.5 kOe, the maximum magnetic entropy change (|ΔSm|max) of the Ni45Co5Mn31Al19 ribbon is about 2 and -1 J·kg−1·K−1 for negative and positive magnetocaloric effects, respectively. Basing on Arrott - Noakes and Kouvel - Fisher methods, critical parameters of the Ni45Co5Mn31Al19 ribbon were determined to be TC ≈ 290 K, β ≈ 0.58, γ ≈ 0.92 and δ ≈ 2.59. The obtained values of the critical exponents indicate that the magnetic order of the alloy ribbon is close to the mean-field model.

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