Influence of Ti atoms on the magnetic order in quaternary NiMnGe:Ti compounds

Martensitic transition assisted modification of the antiferromagnetic ordering in Ge-site doped MnNiGe alloys

“…Apart from the reduction of MPT, the present work revealed (i) helically modulated incommensurate AFM ordering of the low-T martensite phase, (ii) a gradual increase in the incommensurate propagation vector with increasing sample temperature, (iii) a commensurate AFM ordering of the high-T austenite phase, and (iv) the absence of any ferromagnetic ordering in the absence of an external magnetic field. Similar incommensurate AFM ordering with helical modulation has also been reported for Si, Ti, and Cr doped MnNiGe alloys [25][26][27][28]. Along the direction 094422-6 FIG.…”

“…3(b)]. Some previous works on the Mn/Ni-site doped MnNiGe alloys also reported a similar helical magnetic structure of the low-T martensite phase [25][26][27][28]. On the other hand, a simple collinear AFM structure has been observed for the magnetically ordered hexagonal austenite phase.…”

“…The axial next-nearest-neighbor Ising model was sometimes used to explain such a helically modulated magnetic arrangement [27,28,34,35]. This model incorporates anisotropic competing exchange interaction with nearest-neighbor ferromagnetic interaction in a plane perpendicular to the helical magnetic structure's modulation axis [27,28,34,35]. On the other hand, nearest-neighbor FM and next-nearest-neighbor AFM interactions along the modulation axis lead to the helical arrangement of magnetic spins perpendicular to the FM plane.…”

“…Partial substitution of different sites of the parent compound with a suitable foreign element corresponds to a significant change in both structural and magnetic transition temperatures [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. Interestingly, the alloy retains the AFM ordering after doping at the Mn/Ni site, as confirmed by the magnetic and neutron powder diffraction (NPD) analysis [9,10,[15][16][17][18][19][24][25][26][27][28]. On the other hand, the effect of doping at the Ge site is slightly different than Mn/Nisite doping.…”

“…[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23]. In addition, the undoped MnNiGe alloy undergoes multiple phase transformations (structural and magnetic depending on the thermal state of the material), namely, (i) MPT around 470 K from the high-temperature Ni 2 In-type hexagonal austenite phase (space group P6 3 /mmc) to the TiNiSi-type orthorhombic martensite phase (space group Pnma) and (ii) a paramagnetic (PM) to spiral antiferromagnetic (AFM) transition below or around 346 K [8][9][10]16,[24][25][26][27][28].…”