Premartensitic phenomena in the ferro- and paramagnetic phases ofNi2MnGa

Mean field and Monte Carlo simulation studies of premartensitic effects in Ni2MnGa

“…Indeed, premartensitic effects in the NiMnGa alloy have only been reported for compositions around the stoichiometric Ni 2 MnGa. The intermediate structure may appear through a true phase transition [9,12] or not [14]. We point out that both behaviors are compatible with the present results.…”

“…Moreover, the magnetoelastic effects have been confirmed from the experimentally observed dependence of the elastic constants on an external magnetic field [16]. In other studies [14], the authors could not find any indication for an intermediate phase although precursors, clearly related to the magnetization of the sample, have been observed. The temperatures T m , TM and Ti are extremely sensitive to the experiments model composition and atomic ordering of the sample.…”

“…The Curie point T m may vary between 360K to 395K, whereas TM may vary from 175K to 450K. For instance in the sample studied by Stuhr et al [14], T m w 364K and T M « 284K with precursor signs for T > TM-, but no intermediate phase was found. In the sample studied by Zheludev et al [11,12] In this paper we present a microscopic theoretical model aimed to investigate the role of the magnetic coupling in Ni-Mn-Ga.…”

Magnetoelastic behavior of the Heusler Ni2MnGa alloy

“…In addition, in Ni-Mn-Ga alloys close to stoichiometric Ni 2 MnGa but with less Mn content, the premartensitic transition is not observed although a magnetoelastic coupling has been proven to exist. 13 We suggest that this different behavior could be due to the fact that the substitution of Mn by Ni atoms causes an increase in the martensitic transition temperature, 14 and the magnetoelastic coupling is likely to be weaker. These two features imply that the bcc phase transforms to a close-packed one ͑martensitic transition͒ at a temperature higher than the temperature at which the intermediate transition would occur ͑which is essentially controlled by the magnetoelastic coupling͒, and therefore, the micromodulated phase cannot develop independently of the martensitic transition in alloys with low Mn content.…”

A Ginzburg-Landau Theory For Ni-Mn-Ga

“…In many experimental studies the interesting premartensitic phenomena in Ni 2 MnGa have been investigated (Planes, Obrado, Gonzales-Comas and Manosa, 1997;Worgull, Petti and Trivisonno, 1996;Stuhr, Vorderwisch, Kokorin and Lindgard, 1997;Zuo, Su and Wu, 1998;Zheludev, Shapiro, Wochner and Tanner, 1996). However, a satisfying picture of the electronic origin of the intermediate phase of Ni-Mn-Ga has not emerged.…”