The electronic structure of CoMnGe with the hexagonal and orthorhombic crystal structure

Kaprzyk, S.; Nizioł, S.

doi:10.1016/0304-8853(90)90759-j

Cited by 78 publications

(51 citation statements)

References 13 publications

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“…This is confirmed by simply inspecting the M S (230 K, 5 T)-directly below T C at 5 kbar. M S decreases ∼30% from the coupled to the decoupled state, which is also the difference observed from orthorhombic to hexagonal MnCoGe 11 . Such results suggest that the crystallographic transition is now at a lower temperature than the magnetic one, as is observed for Co 0.5 Ni 0.5 MnGe 19 under hydrostatic pressure for P 8 kbar.…”

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confidence: 54%

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Pressure-tuned magnetocaloric effect in Mn0.93Cr0.07CoGe

2011

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Effects of physical and chemical pressures in the Mn 1−x Cr x CoGe series of compounds are studied. Cr substitution and hydrostatic pressure play similar roles in displacing T C to lower temperatures and coupling or decoupling magnetic and crystallographic transitions. In this work the similarities and differences between the effects of chemical and physical pressures are explored, helping unveil the nature of the first-order phase transition presented by MnCoGe-based compounds. DOI: 10.1103/PhysRevB.84.020414 PACS number(s): 75.30.Cr, 75.30.Sg, 75.50.Cc, 75.80.+q Since the discovery of the giant magnetocaloric effect on FeRh 1 and the subsequent observation of a tunable giant entropy change ( S M ) on Gd 5 Ge 2 Si 2 , 2 magnetic refrigeration based on the magnetocaloric effect has gained increasing attention. It is regarded as a promising, more efficient, and environmentally friendly alternative to gas-compression-based refrigeration due to its potential applications in a wide range of temperatures.Materials presenting first-order magnetic phase transitions are of special interest since they intrinsically present high S M originating from the discontinuous character of the transition. These transitions can be observed in a series of low-cost 3d metal-based compounds such as MnAs,Ni 0.5 Mn 0.5 Sn, 5 and (Mn,Fe) 2 (P,As) 1 . 6 Such transitions are always accompanied by a discontinuous change in the lattice parameters and often in volume, but do not always result in a crystal symmetry change. Materials presenting only lattice parameters and/or volume change around the phase transition are said to undergo a magnetoelastic phase transition, e.g., all Fe 2 P-based compounds as well as La(Fe,Si) 13 , 7 while those which also show a change in crystal structure undergo a magnetostructural phase transition, e.g., FeRh, Gd 5 Ge 2 Si 2 , MnAs, and Ni 0.5 Mn 0.5 Sn.Since magnetic interactions are sensitive to interatomic distances, chemical pressure-substitutions, dopings, and interstitial elements-has been largely used to tune magnetic properties. Both magnetic and crystallographic phasetransition temperatures can be tuned using chemical pressure. This allows for first-order phase-transition temperatures to be easily tuned. But, more importantly, it allows for chemical pressure to be used to simultaneously tune separate magnetic and crystallographic transitions to coincide, giving rise to coupled first-order transitions. Thus, chemical pressure is an invaluable tool not only to tune but also to create magnetoelastic and magnetostructural couplings. A good example of both the creation and tuning of a magnetostructural coupling comes from the MnCoGe system.MnCoGe is a 3d metal-based ferromagnet with a Curie temperature (T C ) of ∼345 K and a diffusionless crystallographic phase transition from the low-temperature orthorhombic TiNiSi type to the high-temperature hexagonal Ni 2 In type of structure at ∼650 K. 8,9 In both orthorhombic and hexagonal structures it behaves as a typical ferromagnet with second-order phase trans...

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“…10,11 The magnetic and crystallographic transitions can be coupled in many ways. We have recently reported that the addition of B as an interstitial and the substitution of Cr on the MnCoGe lattice can be used to make the magnetic and structural phase transitions coincide, giving rise to a giant magnetocaloric effect.…”

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Pressure-tuned magnetocaloric effect in Mn0.93Cr0.07CoGe

2011

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“…1,2) The magnetic moment of the orthorhombic structure is larger than that of the hexagonal structure. 1,3,4) The T C and T M of MnCoGe-based compounds have been controlled by substitution of Al 5) or V 6) for Co, offstoichiometric composition, 2,7,8) interstitial modification, 9) and external pressure.…”

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Magnetic and Structural Properties of Metamagnetic MnCo<sub>0.92</sub>Fe<sub>0.08</sub>Ge Compound

et al. 2016

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The magnetic and structural properties of ferromagnetic MnCo 0.92 Fe 0.08 Ge were investigated by magnetization and X-ray powder diffraction measurements in magnetic fields up to 5 T. The compound showed first-order transition between the paramagnetic and ferromagnetic state with a thermal hysteresis of approximately 24 K, which was accompanied by the martensitic transformation from the hexagonal Ni 2 In-type structure to the orthorhombic TiNiSi-type structure in the vicinity of 275 K. The cell volume expanded by 4.1% during the martensitic transformation. The magnetic moment of MnCo 0.92 Fe 0.08 Ge was estimated to be 111 Am 2 kg ¹1 (3.7 ® B /f.u.) at 10 K. The compound showed both metamagnetic transition and magnetic field-induced martensitic transformation.

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“…In the hexagonal phase, the shorter Mn-Mn distances strengthen the exchange coupling leading to broader 3d band width. 20,21 So, the observed giant MCE around T str (approximately 18 J/kg K for DB ¼ 8 T) in the Mn 0.94 Ti 0.06 CoGe compound can be attributed to the combined effect of an abrupt change in magnetization as well as volume in the vicinity of the structural transition (structural entropy change).…”

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“…The reduction of the saturation moment is expected in the hexagonal phase compared with the orthorhombic phase. 20 Fig . 4 shows the sudden drop of magnetization in the vicinity of T str .…”

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On the crystal structure and magnetic properties of the Mn0.94Ti0.06CoGe alloy

Shamba

Wang

Debnath

et al. 2013

Journal of Applied Physics

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Structural and magnetic properties of Mn0.94Ti0.06CoGe have been studied by a combination of bulk magnetisation and neutron diffraction measurements over the temperature range of 5 K–350 K. The crystal structural transition occurs at Tstr (∼235 K) with a change in symmetry from the low temperature orthorhombic TiNiSi-type structure (space group Pnma) to the high temperature hexagonal Ni2In-type structure (space group P63/mmc) and the magnetic phase transition takes place around TC = 270 K. It is found that the structural transition around Tstr is incomplete and there is a co-existence of the orthorhombic and hexagonal structures between Tstr and TC (∼270 K). These results are discussed in connection with the magnetic and magnetocaloric behaviours in Mn0.94Ti0.06CoGe.

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The electronic structure of CoMnGe with the hexagonal and orthorhombic crystal structure

Cited by 78 publications

References 13 publications

Pressure-tuned magnetocaloric effect in Mn0.93Cr0.07CoGe

Pressure-tuned magnetocaloric effect in Mn0.93Cr0.07CoGe

Magnetic and Structural Properties of Metamagnetic MnCo<sub>0.92</sub>Fe<sub>0.08</sub>Ge Compound

On the crystal structure and magnetic properties of the Mn0.94Ti0.06CoGe alloy

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