Abstract
In order to investigate behavior of magnetic field-induced reverse martensitic transformation for Ni-Co-Mn-Sb, magnetization experiments up to a static magnetic field of 18 T and a pulsed magnetic field of 40 T were carried out. In the thermomagnetization curves for Ni41Co9Mn39Sb11 alloy, the equilibrium transformation temperature T0 was observed to decrease with increasing applied magnetic field, μ0H, at a rate of dT0/dμ0H = 4.6 K/T. The estimated value of entropy change evaluated from the Clausius-Clapeyron relation was about 14.1 J/(K·kg), which was in good agreement with the value obtained by differential scanning calorimetric measurements. For the isothermal magnetization curves, metamagnetic behavior associated with the magnetic field-induced martensitic transformation was observed. The equilibrium magnetic field, μ0H0 = (μ0HAf + μ0HMs)/2, of the martensitic transformation tended to be saturated at lower temperature; that is, transformation arrest phenomenon was confirmed for the Ni-Co-Mn-Sb system, analogous with the Ni(Co)-Mn-Z (Z = In, Sn, Ga, Al) alloys. Temperature dependence of the magnetic field hysteresis, μ0Hhys = μ0HAf − μ0HMs, was analyzed based on the model for the plastic deformation introduced by the dislocations. The behavior can be explained by the model and the difference of the sweeping rate of the applied magnetic field was well reflected by the experimental results.
Highlights
Since a new type of magnetic shape memory alloy was reported for off-stoichiometric NiMn-basedHeusler alloys in 2004 [1], related studies have been intensively carried out
X-ray powder diffraction pattern measured at room temperature for Ni41Co9Mn39Sb11 alloy annealed and quenched from 1173 K is shown in Figure 1, together with that for a simulated pattern
The alloy is in the parent phase state at room temperature, and the pattern can be indexed as the L21-type ordered phase
Summary
Heusler alloys in 2004 [1], related studies have been intensively carried out This shape memory alloy is different from the conventional one of Ni-Mn-Ga, in which a large magnetostriction occurs due to a re-arrangement of the martensitic variant [2,3]. Application of a magnetic field decreases the martensitic transformation temperature because of the gain of the Zeeman energy, and magnetic field-induced transformation from the martensite phase to the parent phase occurs This behavior is called the metamagnetic shape memory effect from the experimental fact that almost complete shape recovery was observed during the magnetic field-induced transformation in a Ni-Co-Mn-In specimen in which the strain had been previously introduced [4]. NiMn-based Heusler alloys have attracted interest in both scientific and applicative aspects
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