Phase diagrams of Ni2+xMn1-xGa Heusler alloys from Hubbard Hamiltonian with account of Jahn-Teller effect

2011 ◽  
Vol 1310 ◽  
Author(s):  
Mikhail A. Zagrebin ◽  
Vasiliy D. Buchelnikov ◽  
Sergey V. Taskaev ◽  
Natal’ya Yu. Fedulova
Keyword(s):  
Phase Diagram ◽  
Free Energy ◽  
Phase Transitions ◽  
Phase Diagrams ◽  
Density Of States ◽  
Heusler Alloys ◽  
Teller Effect ◽  
Hubbard Hamiltonian ◽  
Jahn Teller ◽  
Jahn Teller Effect

ABSTRACTIn this work a microscopic Hamiltonian is investigated using the Hubbard model for a ferromagnet with two degenerate bands, taking into account the Jahn-Teller effect. A macroscopic free energy is obtained from the microscopic Hubbard Hamiltonian. All free energy coefficients depend on microscopic parameters: temperature T and composition x. As a result of analytical minimization of free energy, phase diagrams are numerically constructed. It is shown that at certain values of parameters on the phase diagrams there are thermodynamic paths which correspond to experimentally observed sequences of phase transitions. Using density of states spectra for different compositions x the T-x phase diagram is numerically constructed. This phase diagram can theoretically explain experimentally observed behavior of the temperatures of phase transitions.

Phase Transitions in Mixed Jahn–Teller Systems with Competitive Interactions

2006 ◽  
Vol 258-260 ◽  
pp. 130-136
Author(s):  
Anatoly Yakovlevich Fishman ◽  
M.A. Ivanov ◽  
Nickolai Tkachev ◽  
K. Y. Shunyaev ◽  
Michael Zinigrad
Keyword(s):  
Phase Transitions ◽  
Phase Diagrams ◽  
Cation Distribution ◽  
Mixed Crystal ◽  
Stabilization Energy ◽  
Competitive Interactions ◽  
Competing Interactions ◽  
Jahn Teller ◽  
Jahn Teller Effect ◽  
Valence Configuration

Phase diagrams of mixed crystal systems exhibiting the cooperative Jahn–Teller effect are investigated. The competition of Jahn–Teller interaction with a) the preference energy of cation distribution over nonequivalent sublattices or b) stabilization energy of 3d-ion valence configuration is considered. The developed model enables to explain the nature of equilibrium and metastable states, the variety of phase diagrams and its special features in crystals with the competing interactions.

Phase Diagrams of Ni2MnX (X = In, Sn, Sb) Heusler Alloys with Inversion of Exchange Interaction

2008 ◽  
Vol 583 ◽  
pp. 131-146 ◽  
Author(s):  
Vasiliy D. Buchelnikov ◽  
Sergey Taskaev ◽  
M.A. Zagrebin ◽  
Peter Entel
Keyword(s):  
Free Energy ◽  
Phase Transitions ◽  
Exchange Interaction ◽  
Phase Diagrams ◽  
Magnetic Phase ◽  
Landau Theory ◽  
Heusler Alloys ◽  
Magnetic Phase Transitions ◽  
Experimental Phase ◽  
Ginzburg Landau

In this work with the help of the phenomenological Ginzburg-Landau theory of structural and magnetic phase transitions the phase diagrams of Heusler Ni-Mn-X (X = In, Sn, Sb) alloys with the inversion of exchange interaction are investigated. The investigation shows that the type of the phase diagrams in Heusler Ni-Mn-X (X = In, Sn, Sb) alloys depends on the value and sign of the free energy parameters. As it is seen from the analysis of the phase diagrams with the determined values and signs of the parameters of Landau functional there are thermodynamic paths which allow to explain experimental phase transitions in Heusler alloys Ni-Mn-X (X = In, Sn, Sb) and Ni-Co- Mn-X (X = In, Sn, Sb) qualitatively.

Jahn-Teller effect induced phase transitions in CsCuCl3

1979 ◽  
Vol 70 (1) ◽  
pp. 44-46 ◽  
Author(s):  
S. Vasudevan ◽  
A.M. Shaikh ◽  
C.N.R. Rao
Keyword(s):  
Phase Transitions ◽  
Teller Effect ◽  
Jahn Teller ◽  
Jahn Teller Effect
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