Factors governing the structural phase transition temperatures of doped La2CuO4 systems

We report the effect of a short-time vacuum annealing (1073 K during 10 minutes) on structural phase transition temperatures and magneto-structural properties of as-quenched ribbons of the Heusler alloy Ni50.6Mn34.5In14.9. This alloy crystallizes in a single phase cubic B2-type austenite with a Curie point of TCA=284 K that with the lowering in temperature transforms into a martensite with TCM185 K. The direct and reverse martensitic phase transition temperatures were MS=257 K, Mf = 221 K, AS = 239 K, and Af = 266 K. After annealing austenite shows the highly ordered L21-type structure while the average chemical composition as well as the structural and magnetic transition temperatures were shifted to Ni50.2Mn34.3In15.5 and MS = 253 K, Mf = 238 K, AS = 257 K, Af = 265 K, ΔT = 13 K, TCA = 299 K and TCM207 K. In the annealed samples the magnetization changes associated to the magnetic and structural transitions are more abrupt and magnetization isotherms in both the austenitic and martensitic existence region show higher initial magnetic susceptibility and faster approach to saturation. Field-cooled hysteresis loops at 10 K were shifted along the negative H-axis for both samples, but a significant anomaly was evident on the left side of the hysteresis loop for as-quenched ribbons.

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Фазовые превращения в сплавах Fe-=SUB=-100-x-=/SUB=-Si-=SUB=-x-=/SUB=-: исследования ab initio

Физика твердого тела ◽

10.21883/ftt.2020.05.49224.24m ◽

2020 ◽

Vol 62 (5) ◽

pp. 655

Author(s):

М.А. Загребин ◽

М.В. Матюнина ◽

А.Б. Кошкин ◽

В.Д. Бучельников ◽

В.В. Соколовский

Keyword(s):

Phase Transition ◽

Ab Initio ◽

Magnetic Phase ◽

Structural Phase ◽

Field Approximation ◽

Coupling Constants ◽

Magnetic Phase Transitions ◽

Mean Field Approximation ◽

Transition Temperatures ◽

Phase Transition Temperatures

In present work, on the basis of structural and magnetic phase transition temperatures estimated theoretically from the first principles, the concentration phase diagram for Fe100-xSix (9.375 ≤ x ≤ 25.0 at.%) was plotted. Structural phase transition temperatures for the experimentally observed crystal structures were obtained from the structural optimization. The Curie temperatures were estimated from mean field approximation using ab initio calculated exchange coupling constants. Both structural and magnetic phase transitions temperatures are found in qualitative agreement with the experiment. For the whole considered concentration range, structural transitions from the ordered cubic to fully disordered through partially disordered one are appeared with temperature increasing. As for magnetic transformations, ferromagnetic-paramagnetic transition is observed for all compositions, however, it happens in different crystal phases.

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