Magnetic glass in Shape Memory Alloy : Ni45Co5Mn38Sn12

The first order martensitic transition in the ferromagnetic shape memory alloy Ni45Co5Mn38Sn12 is also a magnetic transition and has a large field induced effect. While cooling in the presence of field this first order magnetic martensite transition is kinetically arrested. Depending on the cooling field, a fraction of the arrested ferromagnetic austenite phase persists down to the lowest temperature as a magnetic glassy state, similar to the one observed in various intermetallic alloys and in half doped manganites. A detailed investigation of this first order ferromagnetic austenite (FM-A) to low magnetization martensite (LM-M) state transition as a function of temperature and field has been carried out by magnetization measurements. Extensive cooling and heating in unequal field (CHUF) measurements and a novel field cooled protocol for isothermal MH measurements (FC-MH) are utilized to investigate the glass like arrested states and show a reverse martensite transition. Finally, we determine a field -temperature (HT) phase diagram of Ni45Co5Mn38Sn12 from various magnetization measurements which brings out the regions where thermodynamic and metastable states co-exist in the HT space clearly depicting this system as a 'Magnetic Glass'.Comment: Magnetic field tunes kinetic arrest and CHUF shows devitrification and melting of Magnetic glas

Mechanical Spectroscopy in Fe-Al-Si alloys at Elevated Temperatures

The mechanical spectroscopy response in Fe-25 at.% (Al + Si) and Fe-15 at.% (Al + Si) has been studied in the temperature interval between800 and 1200 K. The solute grain boundary relaxation of aluminium and silicon was strongly dependent of the degree of order in the sample. Adecrease in the order degree allows the development of the solute peak at around 1000K during the cooling from 1200 K. Nevertheless, if the orderdegree is not decreased, the grain boundaries remain locked and consequently the relaxation peak does not appear