Effect of thermal treatments on the structural and magnetic transitions in melt-spun Ni-Fe-Ga-(Co) ribbons

Ţolea, Felicia; Sofronie, M.; Crisan, A.; Enculescu, Monica; Kuncser, V.; Văleanu, M.

doi:10.1016/j.jallcom.2015.07.296

Cited by 22 publications

(10 citation statements)

References 26 publications

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“…The fractured cross-section structure shows that the morphology changes with TT, being a noticeable improvement of the columnar microstructure without equiaxial grains or precipitates (Figure 2d). According to the previous studies performed by our group [24,25], and also as suggested by XRD (Figure 1), the treatment temperature of 400 • C (673 K) is enough to promote the ordering of the structure and the growth of crystallites. We also mentioned that, since the thermal treatment is not performed in situ at SEM, different parts of the samples are imaged before and after annealing.…”

Section: Sem Microscopymentioning

confidence: 67%

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

et al. 2021

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The influence of the rapid solidification technique and heat treatment on the martensitic transformation, magnetic properties, thermo- and magnetic induced strain and electrical resistivity is investigated for the Cu doped NiMnGa Heusler-based ferromagnetic shape memory ribbons. The martensitic transformation temperatures are unexpectedly low (below 90 K—which can be attributed to the disordered texture as well as to the uncertainty in the elements substituted by the Cu), preceded by a premartensitic transformation (starting at around 190 K). A thermal treatment slightly increases the transformation as well as the Curie temperatures. Additionally, the thermal treatment promotes a higher magnetization value of the austenite phase and a lower one in the martensite. The shift of the martensitic transformation temperatures induced by the applied magnetic field, quantified from thermo-magnetic and thermo-magnetic induced strain measurements, is measured to have a positive value of about 1 K/T, and is then used to calculate the transformation entropy of the ribbons. The magnetostriction measurements suggest a rotational mechanism in low fields for the thermal treated samples and a saturation tendency at higher magnetic fields, except for the temperatures close to the phase transition temperatures (saturation is not reached at 5 T), where a linear volume magnetostriction cannot be ruled out. Resistivity and magnetoresistance properties have also been measured for all the samples.

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Section: Sem Microscopymentioning

confidence: 67%

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

et al. 2021

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“…Not finding the effect in bulk, we further sought it in polycrystalline ribbons, prepared by rapid quenching of the melt, as described in the following. For this purpose, we have chosen from the NiFeGa compositions studied in [17] the compound Ni56Fe16Ga28 showing narrow and well defined transformation peaks. Ingots of the mentioned nominal composition have been prepared from high purity elements, by arc melting under argon protective atmosphere and subjected to a thermal treatment in high vacuum for 25 h at 1223 K, followed by a quenching in iced water.…”

Section: Experimental Results For N If Ega Polycrystalline Ribbonsmentioning

confidence: 99%

“…This alloy was previously studied as a cheaper and less brittle alternative to NiMnGa [15] -while keeping a good level of magnetic properties as a ferromagnetic shape memory alloy (FSMA) [16]. In previous works, NiFeGa exhibited the possibility of transformation temperatures or enthalpies tuning [17], showing a rich magnetoresistive behavior [18]. Our focus here is to characterize the thermal memory properties, i.e.…”

Section: Experimental Results For N If Ega Polycrystalline Ribbonsmentioning

confidence: 99%

Thermal memory fading by heating to a lower temperature: Experimental data on polycrystalline NiFeGa ribbons and 2D statistical model predictions

Ţolea

Văleanu

2017

Solid State Communications

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Shape memory alloys are known to memorise one -or several-temperatures at which the martensite-austenite transformation was stopped before completion in the past, the memory manifesting as specific dips in subsequent calorimetric scans. Previous studies have shown that this memory can be erased by heating to higher temperatures than the ones previously recorded. In this paper, we study a distinct memory fading effect which takes place by heating to a lower temperature. This effect is reported in NiFeGa as polycrystalline ribbons, the alloy being initially studied as bulk for which the thermal memory effect was not found. If, after an initial incomplete heating up to T1 one performs a second incomplete heating up to T2 < T1, a new calorimetric dip appears at T2, as expected, while less expected was that the dip corresponding to T1 reduces in amplitude or even vanishes (if the arrest at T2 is repeated). The memory fading effect is more clear for small differences T1 − T2 and less obvious or absent for large ones. The second part of the paper employs a statistical 2D model, which associates the memorized temperatures with a depletion of certain martensite plates sizes, and also supports the memory fading effect.

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“…An alloy with the nominal composition Ni 52 Co 2 Fe 20 Ga 26 (Tolea et al, 2015), denoted Ga26 in the following, was prepared from high-purity elements by arc melting in an argon atmosphere. The ingot was inductively melted in a quartz tube (nozzle diameter of 0.5 mm) under an argon atmosphere and then rapidly quenched by the melt-spinning technique.…”

Section: Methodsmentioning

confidence: 99%

Long- and short-range order in the Ni₅₂Co₂Fe₂₀Ga₂₆ ferromagnetic Heusler alloy

Macovei¹,

Ţolea²

2021

J Appl Cryst

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The crystalline structure and Fe local environment in a Co-doped Ni–Fe–Ga Heusler alloy, prepared by the melt-spinning technique, were investigated by X-ray diffraction (XRD) and EXAFS at room and low temperatures. The characteristic temperatures of the austenite–martensite phase transitions were determined by differential scanning calorimetry via cooling and heating cycles of the alloy ribbons. As shown by room-temperature XRD, the austenitic phase of the alloy has the chemically ordered L21 Heusler structure. This was confirmed by EXAFS, although this technique was not able to conclusively distinguish between the L21 and B2 structures of the austenite for the analyzed alloy. The low-temperature martensitic phase and its structural evolution towards austenite with increasing temperature were studied by high-energy X-ray diffraction, which evinced the martensite modulation. However, the Fe environment could be fitted by EXAFS with the tetragonal L10 structure of the non-modulated martensite. This proves that the martensite modulation has structural effects on a long-range scale, without significant changes in the short-range order around the atoms. The changes in the local structure around iron on martensitic transformation were correlated with changes in the electronic structure, described by XANES spectroscopy at the Fe K edge.

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Effect of thermal treatments on the structural and magnetic transitions in melt-spun Ni-Fe-Ga-(Co) ribbons

Cited by 22 publications

References 26 publications

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

Thermal memory fading by heating to a lower temperature: Experimental data on polycrystalline NiFeGa ribbons and 2D statistical model predictions

Long- and short-range order in the Ni₅₂Co₂Fe₂₀Ga₂₆ ferromagnetic Heusler alloy

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Effect of thermal treatments on the structural and magnetic transitions in melt-spun Ni-Fe-Ga-(Co) ribbons

Cited by 22 publications

References 26 publications

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

Magnetic and Magnetostrictive Properties of Ni50Mn20Ga27Cu3 Rapidly Quenched Ribbons

Thermal memory fading by heating to a lower temperature: Experimental data on polycrystalline NiFeGa ribbons and 2D statistical model predictions

Long- and short-range order in the Ni52Co2Fe20Ga26 ferromagnetic Heusler alloy

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Long- and short-range order in the Ni₅₂Co₂Fe₂₀Ga₂₆ ferromagnetic Heusler alloy