Effect of Ni/Mn ratio on phase transformation and magnetic properties in Ni-Mn-In alloys

The effect of variation in Ni/Mn ratio on structure, phase transformation, and magnetic properties was investigated in the Ni(50-x)Mn(37+x)In(13) alloys. Small change in the Ni/Mn ratio drives the structure from martensite of tetragonal L1(0) to austenite of cubic L2(1) at room temperature. With decrease in Ni/Mn ratio or increase in Mn content the martensitic transformation temperature was found to decrease and the alloys do not undergo phase transformation below a critical value (7.86) of valence electron concentration (e/a). Temperature and field dependence of magnetization data reveals the complex magnetic nature arising from the coexistence of ferromagnetic and antiferromagnetic interactions in the system. It was found that the effect of Ni/Mn. and Mn/In ratios on phase transformation and magnetic properties in Ni-Mn-In alloys is similar if the e/a value of the alloy system remains unchanged. (C) 2010 [doi: 10.1063/1.3467966

Microstructure, magnetic properties and magnetocaloric effect in melt-spun Ni-Mn-Ga ribbons

Structural transformation, microstructure and magnetocaloric effect (MCE) were investigated in melt-spun Ni(55)Mn(20.6)Ga(24.4) and Ni(55)Mn(19.6)Ga(25.4) ribbons. Magnetic and thermal studies of the ribbons revealed the occurrence of simultaneous structural and magnetic transitions near room temperature with a narrow thermal hysteresis of magnetization approximate to 2 K. Maximum entropy changes (Delta S(M)) of -9.5 and -10.4J/kg K have been obtained at 309 K for a field change of 2 T in Ni(55)Mn(20.6)Ga(25.4) and Ni(55)Mn(19.6)Ga(25.4) ribbons, respectively. The Ni(55)Mn(19.6)Ga(25.4) ribbon exhibits refrigeration capacity (RC) of 47 J/kg with low average hysteresis loss (approximate to 1.5J/kg) at the merged structural and magnetic transition temperature. (C) 200

In-situ phase transformation studies of Ni48Mn39In13 melt-spun ribbons

The phase transformation in Ni48Mn39In13 melt-spun ribbons has been studied by employing in-situ transmission electron microscopy (TEM) techniques. At room temperature, the investigations showed the martensite phase consisting of plates with internal stacking faults. This phase exhibited the presence of 7M and 5M modulations. In addition, a small volume fraction of the austenite phase was observed. Upon in-situ heating from room temperature to 95 degrees C, the martensite phase transformed to austenite phase. However, in the subsequent cooling-heating cycles, the martensite phase was retained at high temperature. We discuss our experimental observations and the possible mechanisms for the stabilization of the martensite phase due to thermal cycling. (c) 2012 Elsevier Ltd. All rights reserved

Coupled magnetostructural transformations in melt-spun Ni(55)Mn(19.6)Ga(25.4) ribbon: An electron spin resonance study

Electron spin resonance study has been carried out on melt-spun ribbon of Ni(55)Mn(19.6)Ga(25.4) exhibiting coupled magnetostructural transition. The correlation of electron spin resonance, thermal and magnetic results permitted a clear distinction of various phases and their transformations. Both structural and magnetic transitions coexist in the temperature range 300 <= T <= 310 leading to four different magnetic phases namely paramagnetic austenite, ferromagnetic austenite, paramagnetic martensite, and ferromagnetic martensite. The sample exhibits a single paramagnetic austenite phase above 310 K while it shows a ferromagnetic martensite phase below 260 K. (C) 2009 [DOI: 10.1063/1.3148863

Structure, magneto-structural transitions and magnetocaloric properties in Ni50-xMn37+xIn13 melt spun ribbons

Melt spun Ni50-xMn37+xIn13 (2 <= x <= 5) ribbons were investigated for the structure, microstructure, magneto-structural transitions and inverse magnetocaloric effect (IMCE) associated with the first-order martensitic phase transition. The influence of excess Mn in Ni site (or Ni/Mn content) on the martensite transition and the associated magnetic and magnetocaloric properties are discussed. It was found that with the increase in Mn content, the martensitic transition shifted from 325 to 240 K as x is varied from 2 to 4, and the austenite phase was stabilized at room temperature. The x=5 ribbon did not show the martensitic transition. For the x=3 ribbon, the structural and magnetic transitions are close together unlike in the x=4 ribbon in which they are far (similar to 60 K) apart. The zero field cooled and field cooled curves support the presence of exchange bias blocking temperature due to antiferromagnetic interactions in the ribbons. A large change in the magnetization between the martensite and austenite phases was observed for a small variation in the Ni/Mn content, which resulted in large IMCE. A large positive magnetic entropy change (Delta S-M) of 32 J/kg K at room temperature (similar to 300 K) for a field change of 5 T with a net refrigeration capacity of 64 J/kg was obtained in the Ni47Mn40In13 ribbon. (C) 2011 Elsevier B.V. All rights reserved

Environmental hydrogeochemistry and genesis of fluoride in groundwaters of Dindigul district, Tamilnadu (India)

Fluoride (F-) is an indispensable element for the human’s skeletal and dental health at prescribed levels and becomes lethal at higher levels. Spatial–temporal variability of F- and its geochemical control/association with other dissolved ions in groundwater in the Dindigul district of Tamilnadu (India) were conducted to describe the geochemical dynamics of F– in response to seasonal variability. High concentrations of fluoride (≥1.5 mg L-1) were observed in the northern region of the district. High levels of F- were observed in non-monsoon periods and low levels in monsoon, because of dilution by precipitation. Bicarbonate was well correlated with F- which explains that both ions were derived from the weathering. While F- has a very weak correlation with silica, this implies that the silicate weathering does not supply F- to the groundwater system. The F- pollution in Dindigul groundwaters is mainly driven by two factors: (1) the geogenic weathering inputs, the geology of this area mainly comprises fluoride bearing minerals (e.g. hornblende biotite gneiss and charnockite); (2) the anthropogenic inputs (agri-fertilizers and tannery waste). Further, F- in the study area is mainly attributed to geogenic sources during pre and postmonsoons and anthropogenic sources in monsoon periods