Effect of pressure and high magnetic field on phase transitions and magnetic properties of Ni1.92Mn1.56Sn0.52 and Ni2MnSn Heusler compounds

An Ab Initio Study of Pressure-Induced Changes of Magnetism in Austenitic Stoichiometric Ni2MnSn

“…We have not found any other stable magnetic state except for that one exhibiting the magnetic moment = 4.09 per 4-atom formula unit of Ni MnSn. This value is higher than the reported experimental value of 3.63 per 4-atomic formula unit [ 6 ] and we will extensively discuss this discrepancy below.…”

“…As the stoichiometic samples in Ref. [ 6 ] were cooled relatively slowly down to the room temperature, it is possible that (i) some Mn-Ni, Mn-Sn and Ni-Sn swaps were created at elevated temperatures but (ii) the system did not equilibrate during the slow cooling due to insufficient diffusion at lower temperatures (an experimentally detected concentration of vacancies is only 500 ppm [ 64 ]) and (iii) the defects stayed frozen in as regions (coherent inclusions) in the single-crystal lattice sharing the lattice parameter with the surrounding defect-free Ni MnSn lattice. It is nevertheless difficult to estimate how numerous would the swaps be and how would the swapped Mn atoms couple to other Mn atoms.…”

“…We have performed an ab initio study of a series of stoichiometric Ni MnSn states with austenitic (full Heusler type) structure using 16-atom computational supercells. In particular, we have focused on pressure-induced changes in their magnetic state as we have our own experimental data for austenitic Ni MnSn [ 6 ]. Motivated by the facts that our calculations (i) give the total magnetic moment of the defect-free stoichiometric Ni MnSn higher than the experimental value by 12.8% and (ii) predict it to be more sensitive to hydrostatic pressures, our study was focused on the role of point defects in this material.…”

“…The presented values of experimental d(ln d p ) were determined as (d d p ). To avoid unreliable values of d(ln )/d p , the effect of pressure on saturated magnetization (5K,5T) of the alloy, d(ln (5K,5T))/d p = 0.2)·10 GPa , has been presented in our previous paper [ 6 ] suggesting that it is the most suitable magnitude for a description of the effect of pressure on the magnetic ground state of the alloy.…”

“…The stoichiometric austenite Ni Mn-based alloys crystallize in the cubic Fm-3m structure (L2 , full Heusler) and exhibit a long range ferromagnetic arrangement of moments below the Curie temperature, see, e.g., Ref. [ 6 ] and references therein.…”