Electronic structure and magnetism of epitaxial Ni–Mn–Ga(-Co) thin films with partial disorder: a view across the phase transition

Schleicher, Benjamin; Klar, D.; Ollefs, Katharina; Diestel, Anett; Walecki, D.; Weschke, E.; Schultz, L.; Nielsch, Kornelius; Fähler, S.; Wende, Heiko; Gruner, Markus E.

doi:10.1088/1361-6463/aa8e7c

Cited by 13 publications

(13 citation statements)

References 86 publications

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“…The Ni 50 14 (Sn for Mn) alloys were prepared by arc melting appropriate proportion of constituent components with a purity better than 99.9 wt.% under an argon atmosphere. The as-cast samples were wrapped by tantalum foil and annealed in a high-vacuum quartz tube at 1173 K for 96 h, followed by quenching in ice water.…”

Section: Methodsmentioning

confidence: 99%

The Effect of Different Atomic Substitution at Mn Site on Magnetocaloric Effect in Ni50Mn35Co2Sn13 Alloy

Xing,

Zhang,

Long

et al. 2018

Crystals

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The effect of different atomic substitutions at Mn sites on the magnetic and magnetocaloric properties in Ni50Mn35Co2Sn13 alloy has been studied in detail. The substitution of Ni or Co for Mn atoms might lower the Mn content at Sn sites, which would reduce the d-d hybridization between Ni 3d eg states and the 3d states of excess Mn atoms at Sn sites, thus leading to the decrease of martensitic transformation temperature TM in Ni51Mn34Co2Sn13 and Ni50Mn34Co3Sn13 alloys. On the other hand, the substitution of Sn for Mn atoms in Ni50Mn34Co2Sn14 would enhance the p-d covalent hybridization between the main group element (Sn) and the transition metal element (Mn or Ni) due to the increase of Sn content, thus also reducing the TM by stabilizing the parent phase. Due to the reduction of TM, a magnetostructural martensitic transition from FM austenite to weak-magnetic martensite is realized in Ni51Mn34Co2Sn13 and Ni50Mn34Co2Sn14, resulting in a large magnetocaloric effect around room temperature. For a low field change of 3 T, the maximum ∆SM reaches as high as 30.9 J/kg K for Ni50Mn34Co2Sn14. A linear dependence of ΔSM upon μ0H has been found in Ni50Mn34Co2Sn14, and the origin of this linear relationship has been discussed by numerical analysis of Maxwell’s relation.

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Section: Methodsmentioning

confidence: 99%

The Effect of Different Atomic Substitution at Mn Site on Magnetocaloric Effect in Ni50Mn35Co2Sn13 Alloy

Xing,

Zhang,

Long

et al. 2018

Crystals

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“…To some extentt his can be controlled by partial disorder and by forcinge xcessC ot ot he Y-and Z-sites.A sd iscussed in Ref. [160],t he same is true for Mn forced to the X-sites (for instance by adjusting the compositiona si n Ni 45 Mn 32 Ni 23 ). In this case,M np artially acquires the similar minority spin density of states to that of Ni, exhibiting ap redominately itinerant behavior, whereas Co atoms placed in the same configurational environmenta st he Mn atoms also acquire magnetic properties similar to Mn.…”

Section: Ni-mn-x(-co) Heusler Alloysmentioning

confidence: 99%

“…[44,[148][149][150][151][152][153][154] Also quaternary systemsa sN i-Mn-In-Co have been investigated. [155][156][157][158][159] TheI n-and Ga-based compounds are isoelectronic and show similar behaviors at the samec ompositions.T herefore, we will discuss in the following the exchange parameters of off-stoichiometric Heusler compounds,w hich we calculatedr ecently for Ni 43 Co 9 Mn 27 Ga 21 [160] under the assumption of additional partial disorder between the X-and Y-sublattices in the L2 1 pro- totype structure X 2 YZ, which are predominately occupied by Mn and Ga. In addition, the Co-rich composition, which forces Co to occupyY -a nd Z-sitesa sw ell, leads to av ariety of additional possibilities for the magnetic exchange interaction pairs presenti nt he system.…”

Section: Ni-mn-x(-co) Heusler Alloysmentioning

confidence: 99%

Hysteresis Design of Magnetocaloric Materials—From Basic Mechanisms to Applications

et al. 2018

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Magnetic refrigeration relies on a substantial entropy change in a magnetocaloric material when a magnetic field is applied. Such entropy changes are present at first‐order magnetostructural transitions around a specific temperature at which the applied magnetic field induces a magnetostructural phase transition and causes a conventional or inverse magnetocaloric effect (MCE). First‐order magnetostructural transitions show large effects, but involve transitional hysteresis, which is a loss source that hinders the reversibility of the adiabatic temperature change ΔTad. However, reversibility is required for the efficient operation of the heat pump. Thus, it is the mastering of that hysteresis that is the key challenge to advance magnetocaloric materials. We review the origin of the large MCE and of the hysteresis in the most promising first‐order magnetocaloric materials such as Ni–Mn‐based Heusler alloys, FeRh, La(FeSi)13‐based compounds, Mn3GaC antiperovskites, and Fe2P compounds. We discuss the microscopic contributions of the entropy change, the magnetic interactions, the effect of hysteresis on the reversible MCE, and the size‐ and time‐dependence of the MCE at magnetostructural transitions.

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“… with the c T / a T ‐ratio of the tetragonal building block as only input parameter. The four sublattices in this structure were occupied with Ni, Mn, Ga, and Co according to the measured composition, considering the results for the sublattice occupation described elsewhere …”

Section: Methodsmentioning

confidence: 99%

Probing the Martensitic Microstructure of Magnetocaloric Heusler Films by Synchrotron Diffraction

et al. 2018

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First‐order, magnetocaloric materials are promising for energy efficient solid‐state cooling because of their high entropy changes, but they have the drawback of a hysteresis due to the nucleation and growth of the involved phases. Here, synchrotron based X‐ray diffraction is used to investigate epitaxial Ni−Mn−Ga−Co thin films grown on Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMN‐PT). This integral method is used to test several hypotheses regarding structure and orientation of the martensite, whose nucleation was proposed to be the decisive contribution to hysteresis in Heusler materials. The measurements are compared to a recently proposed model of the martensitic nuclei, combining the phenomenological martensite theory with the adaptive concept. This investigation demonstrates that the diffraction patterns are consistent with a martensitic nucleus built from 8 variants forming a‐b laminates. Additionally, it is shown that in accordance with the surface morphology of these films only a subset of nuclei occur, namely those needed to form type X martensite.

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Electronic structure and magnetism of epitaxial Ni–Mn–Ga(-Co) thin films with partial disorder: a view across the phase transition

Cited by 13 publications

References 86 publications

The Effect of Different Atomic Substitution at Mn Site on Magnetocaloric Effect in Ni50Mn35Co2Sn13 Alloy

The Effect of Different Atomic Substitution at Mn Site on Magnetocaloric Effect in Ni50Mn35Co2Sn13 Alloy

Hysteresis Design of Magnetocaloric Materials—From Basic Mechanisms to Applications

Probing the Martensitic Microstructure of Magnetocaloric Heusler Films by Synchrotron Diffraction

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