scholarly journals The Characteristic Properties of Magnetostriction and Magneto-Volume Effects of Ni2MnGa-Type Ferromagnetic Heusler Alloys

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3655 ◽  
Author(s):  
Sakon ◽  
Yamasaki ◽  
Kodama ◽  
Kanomata ◽  
Nojiri ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Spin Fluctuation ◽  
Heusler Alloys ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Itinerant Electron ◽  
Valence Electron Concentration ◽  
Lattice Softening ◽  
The Magnetic Field ◽  
Volume Effects

In this article, we review the magnetostriction and magneto-volume effects of Ni2MnGa-type ferromagnetic Heusler alloys at the martensitic, premartensitic, and austenitic phases. The correlations of forced magnetostriction (ΔV/V) and magnetization (M), using the self-consistent renormalization (SCR) spin fluctuation theory of an itinerant electron ferromagnet proposed by Takahashi, are evaluated for the ferromagnetic Heusler alloys. The magneto-volume effect occurs due to the interaction between the magnetism and volume change of the magnetic crystals. The magnetic field-induced strain (referred to as forced magnetostriction) and the magnetization are measured, and the correlation of magnetostriction and magnetization is evaluated. The forced volume magnetostriction ΔV/V at the Curie temperature, TC is proportional to M4, and the plots cross the origin point; that is, (M4, ΔV/V) = (0, 0). This consequence is in good agreement with the spin fluctuation theory of Takahashi. An experimental study is carried out and the results of the measurement agree with the theory. The value of forced magnetostriction is proportional to the valence electron concentration per atom (e/a). Therefore, the forced magnetostriction reflects the electronic states of the ferromagnetic alloys. The magnetostriction near the premartensitic transition temperature (TP) induces lattice softening; however, lattice softening is negligible at TC. The forced magnetostriction at TC occurs due to spin fluctuations of the itinerant electrons. In the martensitic and premartensitic phases, softening of the lattice occurs due to the shallow hollow (potential barrier) of the total energy difference between the L21 cubic and modulated 10M or 14M structures. As a result, magnetostriction is increased by the magnetic field.

SPIN FLUCTUATION THEORY FOR TEMPERATURE-INDUCED FERROMAGNETISM IN ITINERANT ANTIFERROMAGNETS AND PARAMAGNETS

1995 ◽  
Vol 09 (10) ◽  
pp. 1171-1184 ◽  
Author(s):  
A.A. POVZNER ◽  
D.V. LIKHACHEV
Keyword(s):  
Order Parameter ◽  
Magnetic Phase ◽  
Spin Fluctuation ◽  
Density Wave ◽  
Spin Density Wave ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Itinerant Electron ◽  
Electron Systems ◽  
Antiferromagnetic Transition

The possible occurrence of “temperature-induced ferromagnetism” in itinerant antiferromagnets with spin-density wave and strong paramagnets is discussed on the basis of spin fluctuation theory taking account of the effect of large ferromagnetic spin fluctuations. It is shown that the presence of a point of inflexion of the density of states near the Fermi level leads to the appearance of temperature-induced ferromagnetic order parameter in the itinerant electron systems. In addition the influence of this order parameter on the antiferromagnetic transition temperature is demonstrated and new mechanism of the magnetic phase transition is studied in relation to the magnetism of TiBe 2.

scholarly journals Forced Magnetostrictions and Magnetizations of Ni2+xMnGa1−x at Its Curie Temperature

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2115 ◽  
Author(s):  
Takuo Sakon ◽  
Yuhi Hayashi ◽  
Dexin Li ◽  
Fuminori Honda ◽  
Gendo Oomi ◽  
...  
Keyword(s):  
Curie Temperature ◽  
Spontaneous Magnetization ◽  
Spin Fluctuation ◽  
Magnetic Moments ◽  
Critical Index ◽  
Fluctuation Theory ◽  
Experimental Investigations ◽  
Valence Electron Concentration ◽  
Martensitic Transition ◽  
The Relationship

Experimental investigations into the field dependence of magnetization and the relationship between magnetization and magnetostriction in Ni2+xMnGa1−x (x = 0.00, 0.02, 0.04) alloy ferromagnets were performed following the self-consistent renormalization (SCR) spin fluctuation theory of itinerant ferromagnetism. In this study, we investigated the magnetization of and magnetostriction on Ni2+xMnGa1−x (x = 0.02, 0.04) to check whether these relations held when the ratio of Ni to Ga and, the valence electron concentration per atom, e/a were varied. When the ratio of Ni to Ga was varied, e/a increased with increasing x. The magnetization results for x = 0.02 (e/a = 7.535) and 0.04 (e/a = 7.570) suggest that the critical index δ of H ∝ Mδ is around 5.0 at the Curie temperature TC, which is the critical temperature of the ferromagnetic–paramagnetic transition. This result confirms Takahashi’s spin fluctuation theory and the experimental results of Ni2MnGa. The spontaneous magnetization pS slightly decreased with increasing x. For x = 0.00, the spin fluctuation parameter in k-space (momentum space; TA) and that in energy space (T0) were obtained. The relationship between peff/pS and TC/T0 can also be explained by Takahashi’s theory, where peff indicates the effective magnetic moments. We created a generalized Rhodes-Wohlfarth plot of peff/pS versus TC/T0 for other ferromagnets. The plot indicates that the relationship between peff/pS and T0/TC follows Takahashi’s theory. We also measured the magnetostriction for Ni2+xMnGa1−x (x = 0.02, 0.04). As a result, at TC, the plot of the magnetostriction (ΔL/L) versus M4 shows proportionality and crosses the origin. These magnetization and magnetostriction results were analyzed in terms of Takahashi’s SCR spin fluctuation theory. We investigated the magnetostriction at the premartensite phase, which is the precursor state to the martensitic transition. In Ni2MnGa system alloys, the maximum value of magnetostriction is almost proportional to the e/a.

Magnetocaloric Effect in Ni-Mn-Ga and Ni-Co-Mn-In Heusler Alloys

2009 ◽  
Vol 1200 ◽  
Author(s):  
Vasiliy Buchelnikov ◽  
Sergey Taskaev ◽  
Mikhail Drobosyuk ◽  
Vladimir Sokolovskiy ◽  
Viktor Koledov ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetocaloric Effect ◽  
Curie Point ◽  
Direct Method ◽  
Heusler Alloys ◽  
Field Change ◽  
Adiabatic Temperature Change ◽  
Magnetic Field Change ◽  
A Direct Method ◽  
The Magnetic Field

AbstractThe positive magnetocaloric effect (MCE) in the vicinity of the Curie point in Ni2+xMn1-xGa (x=0.33, 0.36, 0.39) Heusler alloys and the negative and positive MCE near the metamagnetostructural (MMS) transition and the Curie point, respectively, in Ni45Co5Mn36.5In13.5 Heusler alloy has been measured by a direct method. For the magnetic field change ΔH = 2 T, the maximal adiabatic temperature change ΔTad at the Curie point in Ni2+xMn1-xGa alloys is larger than 0.6 K. For Ni45Co5Mn36.5In13.5 alloy, the maximal value of ΔTad = 1.68 K (for the same magnetic field change, ΔH = 2 T) is observed at the MMS phase transition temperature.

Extended Dynamic Spin-Fluctuation Theory with Application to Iron

2012 ◽  
Vol 190 ◽  
pp. 55-58 ◽  
Author(s):  
B.I. Reser ◽  
N.B. Melnikov ◽  
Vladimir I. Grebennikov
Keyword(s):  
Phase Transition ◽  
Magnetic Properties ◽  
Green Function ◽  
Spin Fluctuation ◽  
Spin Fluctuations ◽  
Fluctuation Theory ◽  
Dynamic Spin ◽  
Discontinuous Phase ◽  
The Mean ◽  
Extended Dynamic

The problem of discontinuous phase transition in the dynamic spin-fluctuation theory is resolved by taking into account large anharmonic spin fluctuations and nonlocality of the mean Green function. The extended theory is applied to the calculation of magnetic properties of iron.

METAMAGNETISM AND SPIN FLUCTUATIONS IN Co-BASED INTERMETALLIC COMPOUNDS

1993 ◽  
Vol 07 (01n03) ◽  
pp. 788-793 ◽  
Author(s):  
TSUNEAKI GOTO ◽  
TOSHIRO SAKAKIBARA
Keyword(s):  
Ground State ◽  
High Field ◽  
Spin Fluctuation ◽  
Spin Fluctuations ◽  
Itinerant Electron ◽  
Metamagnetic Transition ◽  
Paramagnetic Region ◽  
High Field Magnetization ◽  
Transition Field ◽  
Fluctuation Model

High field magnetization and susceptibility of Co-based compounds Y(Co1−xA1x)2 are investigated in the paramagnetic region 0≤x≤0.11. In all the region, a sharp metamagnetic transition is observed, while the susceptibility shows a maximum at finite temperature Tmax. The transition field Hc exhibits a positive shift proportional to T2 with temperature. The Hc in the ground state is found to be proportional to Tmax. The experimental results are discussed with a new theory for itinerant electron metamagnetism based on the spin fluctuation model.

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