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An investigation on the relationship between magnetostriction and magnetization by means of the self-consistent renormalization (SCR) theory of an itinerant ferromagnet was performed for Ni2MnGa alloy. The magnetization results at the Curie temperature TC suggest that the critical index δ of H ∝ Mδ is 4.7–5.0, and this confirms Takahashi's spin fluctuation theory and the result of Nishihara et al. As a result, at TC, the relation between magnetostriction and M2 deviates from proportionality and the magnetostriction is proportional to M4. At TC, the plot of ΔL/L vs M4 crossed the point of origin. This result is in accordance with Takahashi's spin fluctuation theory. [ABSTRACT FROM AUTHOR]

Abstract: The objective of this paper is the investigation of the correlations between crystal structure and the magnetization of Ni–Mn–Ga Heusler alloy. Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloy Ni52Mn25Ga23 were performed across the martensite transition temperature T M and reverse martensite transition temperature T R at atmospheric pressure. When cooling from the austenite phase, thermal strain steeply decreases because of martensite transition. Permeability suddenly increases at the Curie temperature T C =358K, indicating ferromagnetism, and suddenly decreases to around T M =328K. This indicates that the lattice transformation and magnetic phase transition correspond to each other. The percentage of contraction by martensite transition at T M and in a magnetic field is twice that in zero fields. Considering with other Ni–Mn–Ga alloys, it is supposed that the magnetic field influences the orientation of the easy c-axis along the magnetic field, and then the variant rearrangement occurs, and consequently, the variation in the strain between zero fields and non-zero field is observed. The measurement results indicate that the regions above and below T M or T R are the ferromagnetic-austenite (Ferro-A) and ferromagnetic-martensite (Ferro-M) phases, respectively. Magnetic phase diagrams were constructed from the results of the temperature dependence of thermal strain. T M and T R increase gradually with magnetic field. T M shift in magnetic fields (B) around zero magnetic field was estimated as dT M /dB=0.46K/T, indicating that magnetization influences martensite transition and the dT M /dB value is the same as that of Ni52Mn12.5Fe12.5Ga23, thereby suggesting the Ferro-M to Ferro-A transition. [Copyright &y& Elsevier]

A system for the simultaneous measurement of magnetization and magnetic strain, which is designed to be used in a pulsed magnetic field, has been developed. In this system, a capacitor on a sample is used and its capacitance changes with the displacement of a sample due to the strain on the sample in a magnetic field. Using this system, we have studied the magnetization and magnetic field-induced strain (MFIS) of the martensitic metallic compound Fe-31.2%Pd (at. %) at temperatures down to 80 K in martensite phase, which is much lower than the martensitic transformation temperature T_{M} =230 K. A substantial MFIS has been measured under a pulsed magnetic field with the time constant 6 ms, which corresponds to 80 Hz in frequency. [ABSTRACT FROM AUTHOR]

The results of experimental investigations of the crystal structure and magnetization of the magnetic shape memory alloy Ni 2 Mn 1.48 Sn 0.52 are reported. This alloy undergoes the martensitic transition from the cubic L 2 1 -type structure to the orthorhombic 4 O -type one with decreasing temperature. The Curie temperature T C A in the austenite phase is 310 K. The magnetic state just below the martensitic transition temperature T M is the low magnetization state or something like that. With further decrease of temperature, this alloy regains the ferromagnetism. The unit cell volume contracts discontinuously at T M with decreasing temperature. The percentage of the volume change was estimated to be ∼0.7%. The nearest neighbor Ni–Mn and Mn–Mn distances in both austenite and martensite phases of Ni 2 Mn 1.48 Sn 0.52 were estimated using the X-ray diffraction analysis. On the basis of the experimental results, the magnetic properties of Ni 2 Mn 1.48 Sn 0.52 are discussed. • The martensitic transition temperature TM of Ni2Mn1.48Sn0.52 is 308 K. • The unit cell volume change of Ni2Mn1.48Sn0.52 changes discontinuously at TM with the volume contraction of ∼0.7% with decreasing temperature. • The nearest neighbor Ni-Mn and Mn-Mn distances of Ni2Mn1.48Sn0.52 was estimated using the X-ray Rietveld analysis. [ABSTRACT FROM AUTHOR]

• The stoichiometric compound Co 2 NbGa crystallizes in the Heusler-type structure. • Co 2 NbGa is ferromagnetic below the Curie temperature of 351 K. • The spontaneous magnetic moment at 5 K of Co 2 NbGa is 1.81 μB/f.u. • The spectral parameters T 0 of the spin fluctuation are estimated to be 2.1 × 103 K. • The spectral parameters T A of the spin fluctuation are estimated to be 4.7 × 103 K. • The T A value estimated from the M s (T)2 vs. T 2 curve is 6.6 × 103 K. • The field-induced magnetization M 4 around T C is found to be proportional to H / M. The compound Co 2 NbGa crystallizes in the Heusler-type structure. Magnetization measurements of Co 2 NbGa have been made under ambient pressure using a SQUID magnetometer. The spontaneous magnetic moment at 5 K and the Curie temperature are 1.81 μ B /f.u. and 351 K, respectively. Many magnetic properties of the itinerant electron ferromagnets are explained by the Takahashi's spin fluctuation theory. In the Takahashi's spin fluctuation theory, spectral parameters of spin fluctuations, T 0 and T A , are involved in various magnetic properties derived theoretically. In this work, we estimated T 0 and T A of Co 2 NbGa by using the results of magnetization measurements at 5 K: T 0 = 2.1 × 103 K and T A = 4.7 × 103 K. This experiment proved that the squared spontaneous magnetization M s (T)2 is proportional to T 2 at low temperature. The T A value estimated from the M s (T)2 vs. T 2 curve is 6.6 × 103 K. Furthermore, the field-induced magnetization M 4 around T C is found to be proportional to H / M in the low magnetic field region. [ABSTRACT FROM AUTHOR]