Crystal and magnetic structure of the NiMnGe1−nSin System

Abstract

Magnetic and crystallographic nature of the compounds NiMnGe1−nSin (0 ≦ n ≦ 1) are studied in the temperature range from 80 to 1000 K by X‐ray and neutron diffraction, magnetometric and DTA measurements. On the basis of these experimental data, crystallographic and magnetic phase diagram are constructed. The compounds have NiTiSi type structure at low temperatures and they transform into the Ni2In type structure at high temperatures. Magnetic and neutron diffraction measurement revealed the existence of three regions of different types of magnetic orderings: helicoidal (0 ≦ n ≦ 0.25), noncollinear (0.3 ≦ n ≦ 0.55), and ferromagnetic (0.6 ≦ n ≦ 1.0). The transition from antiferromagnetic to ferromagnetic phase implies the decrease of the MnMn distances.

Coupled Magnetic and Structural Transitions in Fe-Doped MnNiSi Compounds

“…Stoichiometric MnNiSi [15], [16] MM'X compound undergoes a hexagonal-to-orthorhombic MT at 1210 K in paramagnetic state. The martensitic phase is a typical ferromagnet with a high T C M at 622 K. Based on substitution of main-group elements [16], alloying MnNiSi with MnNiGe, the structural and magnetic properties were studied. However, it is difficult to decrease T t of MnNiSi to RT.…”

“…In order to achieve this magnetostructural coupling, many effective methods have been implied, such as the application of chemical substitution [5], [9], [10], vacancy introduction [11]- [13], applying pressure [14]. Stoichiometric MnNiSi [15], [16] MM'X compound undergoes a hexagonal-to-orthorhombic MT at 1210 K in paramagnetic state. The martensitic phase is a typical ferromagnet with a high T C M at 622 K. Based on substitution of main-group elements [16], alloying MnNiSi with MnNiGe, the structural and magnetic properties were studied.…”

Magnetocaloric effect and negative thermal expansion in hexagonal Fe doped MnNiGe compounds with a magnetoelastic AFM-FM-like transition

“…The family of hexagonal MM ’ X (M, M ’ = transition metals, X  = carbon or boron group elements) compounds has been extensively investigated over the past few decades1234. Among these materials, the stoichiometric MnNiGe alloy undergoes separate magnetic and crystallographic transitions during cooling and is absent of a first-order magnetostructural phase transition (FOMST).…”

“…Among these materials, the stoichiometric MnNiGe alloy undergoes separate magnetic and crystallographic transitions during cooling and is absent of a first-order magnetostructural phase transition (FOMST). In recent years, numerous successful attempts have been made to tune these two separate transformations simultaneously to coincide through the chemical modification3456789, physical pressure1011, or alternation of sample form (from bulk to ribbon)1213, and the introduction of atom vacancies14. During the cooling process, such a coincidence can arouse a FOMST from a paramagnetic (PM) Ni 2 In-type hexagonal austenitic to an antiferromagnetic (AFM) or a ferromagnetic (FM) TiNiSi-type orthorhombic martensitic phase.…”

Windows open for highly tunable magnetostructural phase transitions

“…14,21 This is why MnNiSi was chosen, whose MT temperature (T t ) and T C M are as high as 1200 K and 622 K, respectively. [29][30][31] In Mn 1−y Co y NiGe system, by doping Co atoms at Mn sites, a 230-K CTW from room temperature to 120 K was opened by simultaneously decreasing the MTs and converting the spiral antiferromagnetic (AFM) martensite to ferromagnetic (FM) state. Within the CTW, a giant MCE of −40 J kg −1 K −1 in a field change of 50 kOe was observed around 236 K for y = 0.1.…”