Magnetic Field-induced Martensitic Transformations in Disordered and Ordered Fe–Pt Alloys

Abstract

Magnetic field-induced martensitic transformations in disordered and ordered Fe-24 at%Pt alloys were studied to examine the effect of degree of order (S) on the transformations by measuring the m agnetization and electrical resistivity, applying a pulsed ultra-high magnetic field. As a result, it is found that a magnetic field higher than a critical strength is needed to induce the martensitic transformations at temperatures above M without regard to the degree of order. The critical strength increases with a straight line for the non-thermoelastic alloys with S<0.5, but on a curved line for the thermoelastic ordered alloys with S=0.7-0.8, as if the curve diverges near the respective To temperature. The divergence phenomenon seems to suggest that the To temperature is a maximum one above which martensites can not be induced even though any high magnetic field is applied. The amount of magnetic field-inlarger the amount of martensites becomes. A thermodynamic calculation for the increase of Ms temperature suggests that the effect of a magnetic field on martensitic transformations may result in not only the Zeeman effect but also another unknown effect.

Martensitic Transformation in Shape Memory Alloys under Magnetic Field and Hydrostatic Pressure

“…Based on the equation, H c vs. M s relations have been thermodynamically calculated for the present alloys by using the physical quantities involved in the equation; which were obtained by referring to the previous studies 21) and by measuring in the present study. 4,5) The calculated results are shown in Fig. 2, where the dotted lines indicated with M.S.E., H.F.E., F.M.E.…”

“…Magnetic field and hydrostatic pressure are important in such external fields because there exist some significant differences in magnetic moment and atomic volume between the parent and martensitic states. 3,4) In fact, many reseachers 1,[3][4][5][6][7][8][9] have examined the effects of magnetic field and hydrostatic pressure on martensitic transformations. We also examined them systematically [4][5][6][7][8] and found many interesting phenomena on them.…”

Shape memory ferromagnets

“…Annealing leads to the ordering of these alloys in a Cu 3 Au (L1 2 ) structure. Such ordering is accompanied by a rise in the Curie temperature [162] and a drop in the martensitic transition temperature and leads to a substantial decrease in hysteresis [161] and the appearance of the shape memory effect [163][164][165][166][167][168].…”

The Crystal Structure and Magnetic Properties of Fe<SUB>3</SUB>Pt Martensite Determined by First Principle Calculations

“…The magnetic moment has been measured experimentally as to Fe-24 at%Pt with different degree of order. 7,8) The magnetic moment par Fe atom in creases with degree of order, S, and it becomes about 2.2 at S % 0:8. This value is smaller than the calculated one.…”