The existence of a first order martensite transition in off-stoichiometric Ni 45 Mn 44 Sn 9 In 2 ferromagnetic shape memory Heusler alloy has been clearly observed by thermal, magnetic, and magneto-transport measurements. Field and thermal path dependence of the change in large magnetic entropy and negative magnetoresistance are observed, which originate due to the sharp change in magnetization driven by metamagnetic transition from the weakly magnetic martensite phase to the ferromagnetic austenite phase in the vicinity of the martensite transition. The noticeable shift in the martensite transition with the application of a magnetic field is the most significant feature of the present study. This shift is due to the interplay of the austenite and martensite phase fraction in the alloy. The different aspects of the first order martensite transition, e.g. broadening of the martensite transition and the field induced arrest of the austenite phase are mainly related to the dynamics of coexisting phases in the vicinity of the martensite transition. The alloy also shows a second order ferromagnetic → paramagnetic transition near the Curie temperature of the austenite phase. A noticeably large change in magnetic entropy (ΔS M = 24 J kg −1 K −1 at 298 K) and magnetoresistance (= −33% at 295 K) has been observed for the change in 5 and 8 T magnetic fields, respectively. The change in adiabatic temperature for the change in a magnetic field of 5 T is found to be −3.8 K at 299 K. The low cost of the ingredients and the large change in magnetic entropy very near to the room temperature makes Ni 45 Mn 44 Sn 9 In 2 alloy a promising magnetic refrigerant for real technological application.
The influence of martensite and austenite phase fractions on the magnetocaloric and magnetoresistance (MR) properties has been studied across the first-order magneto-structural martensite transition in the polycrystalline Ni45Mn44Sn7In4 Heusler alloy near room temperature. Here, we have studied in detail the structural, calorimetric, magnetic, magnetocaloric, and magneto-resistance properties of the Ni45Mn44Sn7In4 Heusler alloy. The detailed investigation of thermal and magnetic field path dependent magnetization and resistivity reveals that In incorporation in the alloy increases the martensite transition (MT) temperature, magnetocaloric effect (MCE), and MR properties of the sample at relatively low magnetic fields near the room temperature. The temperature and magnetic field path dependent austenite phase fraction have been calculated using a theoretical model. A strong correlation between observed MR and field induced austenite phase fraction (fFIA) has been established, which reveals that MR does not depend on the parent austenite and martensite phases. This work explores the fundamental phenomena of the interplay of austenite and martensite phase fractions that contribute to the magnetocaloric effect (MCE) and MR properties in In doped Ni-Mn-Sn compounds very close to room temperature. The maximum MR is found to be −36.2% for the change in the 8 T magnetic field, when fFIA is 73.9% at 313 K. The isothermal magnetic entropy change, refrigeration capacity, and adiabatic temperature change are found to be 17.5 J kg−1 K−1, 100.8 J/kg, and −7.2 K, respectively, for the change in the 5 T magnetic field near 315 K.
ARTICLES YOU MAY BE INTERESTED INSurface spin glass and exchange bias effect in Sm 0.5 Ca 0.5 MnO 3 manganites nano particles AIP Advances 1, 032110 (2011); https://doi.org/10.1063/1.3623428The effect of inserted layers on the anomalous Hall effect and perpendicular magnetic anisotropy in Ta In this paper, we have studied low-temperature magnetic properties and transport dynamics of half-doped Pr 0.5 Sr 0.5 MnO 3 (PSMO) nano-manganite. Nanoparticles with different average grain sizes are synthesized using chemical pyrophoric reaction route and exhibit same crystal structure. It is reported that particle size reduction in half-doped PSMO manganite interestingly leads to ferromagnetic (FM) metallic behavior which is accompanied by coupled positive magnetoresistance (PMR) (up to 9%) at fields (H ≤ 1kOe at 50K) and negative magnetoresistance (NMR) (∼59% at 100K) at 80kOe fields. Interestingly, maximum PMR is appeared at much lower than the critical field (30kOe) for the melting of insulating -antiferromagnetic (AFM) ordered state. Moreover, it is found that low-temperature AFM-FM phase transition, T N ∼ 135K is smeared out with reduction of particle size; however, the transition is prominent in bulk material. A metastable magnetic state with a mixed fraction of FM and AFM phases is observed below T N . Superparamagnetic (SPM) behavior of PSMO nanoparticles has been revealed by probing ac-susceptibility measurements. Lowtemperature transport dynamics has been investigated through four probe resistivity and magneto-transport measurements. A size-induced insulating-metallic phase transition is observed on nano dimension in the range of 125-155K under high magnetic fields; however, the bulk counterpart remains insulating over the entire temperature range. The non-trivial electronic-and magnetotransport properties are explained by the inter-grain spin-polarized hopping mechanism through double exchange (DE) interactions. These issues have been revisited and discussed in the framework of enhanced surface disorder, where surface spins plays the crucial role for inter-grain transport dynamics in nanometric dimension. We believe the present field dependent MR holds excellent potential for future spintronic devices and manifests the exotic properties of strongly correlated materials. © 2018 Author(s)
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