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.

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.

Temperature Hysteresis in the Dynamic Spin-Fluctuation Theory for Strong Ferromagnets

2009 ◽  
Vol 152-153 ◽  
pp. 579-582 ◽  
Author(s):  
B.I. Reser ◽  
Vladimir I. Grebennikov ◽  
N.B. Melnikov
Keyword(s):  
Initial Data ◽  
Curie Temperature ◽  
Temperature Dependence ◽  
Catastrophe Theory ◽  
Spin Fluctuation ◽  
Fluctuation Theory ◽  
Magnetic Characteristics ◽  
Temperature Hysteresis ◽  
System Of Equations ◽  
Dynamic Spin

Temperature dependence of magnetic characteristics of Fe and Fe-Ni invar is considered in the dynamic nonlocal approximation of the spin-fluctuation theory. Numerical calculations show that the magnetic characteristics can have a discontinuous jump at high temperatures, well below the Curie temperature. Using methods of the catastrophe theory, we investigate the effect of small changes in the initial data on the results of the calculation. It is demonstrated that the discontinuous jump can only be smoothed but cannot be eliminated entirely without a significant change in the system of equations of the spin-fluctuation theory. Possible variants of such changes are discussed.

The spontaneous magnetization of nickel + copper alloys

1958 ◽  
Vol 248 (1253) ◽  
pp. 145-152 ◽  
Keyword(s):  
Curie Temperature ◽  
Marked Decrease ◽  
Spontaneous Magnetization ◽  
Magnetic Moments ◽  
Copper Alloys ◽  
Nickel Copper ◽  
Wide Range ◽  
Magnetic Techniques ◽  
Good Agreement

The spontaneous magnetization (σ 0 , T ) of a ferromagnetic may be deduced exclusively from the determination of magnetic isothermals, or in conjunction with magnetocaloric measurements. Values of σ 0, T of a nickel + copper alloy containing 30·75 at. % of copper have been obtained near its Curie temperature using both of these techniques and are shown to be in good agreement. Measurements of spontaneous magnetization and Curie temperature ( θ f ) of nickel + copper alloys containing up to 54·11 at. % of copper using the purely magnetic techniques are described. These measurements were performed over a temperature range from θ f down to 80 °K in all cases, and to 23 °K in the cases of alloys containing over 30 at. % of copper. The magnetic moments per atom ( p B ) of the alloys, which are deduced from the measurements, vary linearly over a wide range of composition, extrapolating to p B = 0 at 53 at. % of copper. This value is in good agreement with that obtained by Meyer & Wolff (1958), and contrary to that based on the familiar measurements of Alder (1916). The reduced magnetization-temperature curves of some of the alloys are given and these show a continuous marked decrease in fullness with increasing copper content.

Magnetic Study on Y2M3Co9P7 (M: Transition Metals) with Cation-Ordered Zr2Fe12P7-Type Structure

2019 ◽  
Vol 289 ◽  
pp. 164-169
Author(s):  
Yusuke Kato ◽  
Hiroto Ohta ◽  
Hiroko Aruga Katori
Keyword(s):  
Transition Metals ◽  
Curie Temperature ◽  
Spontaneous Magnetization ◽  
Magnetic Moments ◽  
Hexagonal Structure ◽  
Type Structure ◽  
Magnetic Study ◽  
Pauli Paramagnetism ◽  
Fe And Mn ◽  
The Stability

We successfully synthesized polycrystalline samples of Y2M3Co9P7 (M = Cr, Mn, Fe, Co, Mo, and Ru), which has the Zr2Fe12P7-type hexagonal structure with M and Co selectively occupy the pyramidal site and three tetrahedral ones, respectively. For the case of M = Co, or Y2Co12P7, the itinerant electronic ferromagnetism was observed below the Curie temperature TC = 153 K. For M = Cr, Mn, Fe, and Ru, the ferromagnetism was also observed below TC = 167 K, 229 K, 233 K and 18 K, respectively, whereas for M = Mo, an exchange-enhanced Pauli paramagnetism tool the place of the ferromagnetism. Among compounds with M being 3d transition metals, TC and spontaneous magnetization took the maximum around M = Fe and Mn. This tendency was also seen in the cases of M being 4d transition metals, i.e., M = Ru and Mo. Our result indicates that magnetic moments at the pyramidal site have rather localized nature and largely affect the stability of the ferromagnetism of Y2M3Co9P7 although the ferromagnetism is considered to be mainly derived from three Co sites.

scholarly journals Тепловое расширение зонных ферромагнетиков Co-=SUB=-2-=/SUB=-MeAl (Me = Ti, V, Cr, Mn, Fe, Ni)

2018 ◽  
Vol 60 (3) ◽  
pp. 614
Author(s):  
Н.И. Коуров ◽  
В.В. Марченков ◽  
В.А. Казанцев ◽  
Ю.А. Перевозчикова
Keyword(s):  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Temperature Interval ◽  
Expansion Coefficient ◽  
Spontaneous Magnetization ◽  
Spin Fluctuation ◽  
Magnetic Moments ◽  
Spin Fluctuations ◽  
Magnetic Fluctuation ◽  
Pauli Susceptibility

AbstractThe thermal expansion coefficient (TEC) of Co_2MAl (M = Ti, V, Cr, Mn, Fe, Ni) band ferromagnets is measured in the temperature interval of 80–900 K. The magnetic-fluctuation contribution α_ m , _sf( T ) = α_ m ( T ) + α_sf( T ) to TEC comprised of negative Stoner α_ m ( T ) and positive spin-fluctuation α_sf( T ) contributions is presented. It is assumed that the contribution of α_ m ( T ) component is proportional to the square of spontaneous magnetization. The contribution of α_sf( T ) is stipulated by the effects of inducing local magnetic moments by spin fluctuations and is proportional to the Pauli susceptibility.

MAGNETIC PROPERTIES OF U1-xDyxAlyNi5-y (y=0,1) SYSTEMS

2003 ◽  
Vol 17 (27n28) ◽  
pp. 1453-1460
Author(s):  
ILEANA LUPSA
Keyword(s):  
Magnetic Properties ◽  
Low Temperature ◽  
Spin Fluctuation ◽  
Magnetic Moments ◽  
Transition Temperatures ◽  
Temperature Range ◽  
Fluctuation Model ◽  
Magnetically Ordered

The magnetic properties of U 1-x Dy x Al y Ni 5-y (y=0,1) systems were investigated in the 2(5)–600 K temperature range and for fields up to 80 kOe. The systems having x≥0.2 are magnetically ordered with low transition temperatures and magnetization mainly due to the Dy contribution. The nickel exhibits magnetic moments, very weak in the low temperature range and well-defined effective moments over transition temperatures. The nickel behavior is discussed in terms of the spin fluctuation model.

Investigations into the Precessing Vortex Core Phenomenon in Cyclone Dust Separators

1994 ◽  
Vol 208 (2) ◽  
pp. 147-154 ◽  
Author(s):  
P Yazdabadi ◽  
A J Griffiths ◽  
N Syred
Keyword(s):  
Vortex Core ◽  
Reynolds Numbers ◽  
Frequency Parameter ◽  
Experimental Investigations ◽  
Swirl Number ◽  
Significant Drop ◽  
Precessing Vortex Core ◽  
Dust Separator ◽  
The Relationship

Experimental investigations have been carried out to examine the effect of downstream pipework configurations on the precessing vortex core (PVC) generated within the exhaust region of a cyclone dust separator. Characterization of the PVC using a non-dimensionalized frequency parameter (NDFP) was used to determine the relationship between Reynolds number and geometrical swirl number of the cyclone. The results show that the NDFP tends towards an asymptotic value for Reynolds numbers of about 50 000 and high swirl numbers (> 3.043). This value is reached earlier with lower swirl numbers. It was concluded that any exhaust pipework configuration produced a significant drop in the PVC frequency, and certain configurations either delayed or promoted the development of the PVC.

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