Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point
The nature of the phase transition has been studied in MnNi _1− _x Co _x Ge _0.97 Al _0.03 ( x = 0.20–0.50) through magnetization, differential scanning calorimetry and x-ray diffraction measurements; and the associated reversibility in the magnetocaloric effect has been examined. A small amount of...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | JPhys Energy |
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| Online Access: | https://doi.org/10.1088/2515-7655/acf957 |
| _version_ | 1797674776914821120 |
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| author | Tapas Samanta Chris Taake Laila Bondzio Luana Caron |
| author_facet | Tapas Samanta Chris Taake Laila Bondzio Luana Caron |
| author_sort | Tapas Samanta |
| collection | DOAJ |
| description | The nature of the phase transition has been studied in MnNi _1− _x Co _x Ge _0.97 Al _0.03 ( x = 0.20–0.50) through magnetization, differential scanning calorimetry and x-ray diffraction measurements; and the associated reversibility in the magnetocaloric effect has been examined. A small amount of Al substitution for Ge can lower the structural phase transition temperature, resulting in a coupled first-order magnetostructural transition (MST) from a ferromagnetic orthorhombic to a paramagnetic hexagonal phase in MnNi _1− _x Co _x Ge _0.97 Al _0.03 . Interestingly, a composition-dependent triple point (TP) has been detected in the studied system, where the first-order MST is split into an additional phase boundary at higher temperature with a second-order transition character. The critical-field-value of the field-induced MST decreases with increasing Co concentration and disappears at the TP ( x = 0.37) resembling most field-sensitive MST among the studied compositions. An increase of the hexagonal lattice parameter a _hex near the TP indicates a lattice softening associated with an enhancement of the vibrational amplitude in the Ni/Co site. The lattice softening leads to a larger field-induced structural entropy change (structural entropy change≫ magnetic entropy change, for this class of materials) with the application of a lower field, which results in a larger reversibility of the low-field entropy change (|Δ S _rev | = 6.9 J kg ^−1 K for Δ μ _0 H = 2 T) at the TP. |
| first_indexed | 2024-03-11T22:03:58Z |
| format | Article |
| id | doaj.art-9299699c0bb44f419b5025d15182fd9a |
| institution | Directory Open Access Journal |
| issn | 2515-7655 |
| language | English |
| last_indexed | 2024-03-11T22:03:58Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | JPhys Energy |
| spelling | doaj.art-9299699c0bb44f419b5025d15182fd9a2023-09-25T09:40:01ZengIOP PublishingJPhys Energy2515-76552023-01-015404400210.1088/2515-7655/acf957Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple pointTapas Samanta0https://orcid.org/0000-0002-0964-502XChris Taake1Laila Bondzio2Luana Caron3Faculty of Physics, Bielefeld University , PO Box 100131, Bielefeld D-33501, GermanyFaculty of Physics, Bielefeld University , PO Box 100131, Bielefeld D-33501, GermanyFaculty of Physics, Bielefeld University , PO Box 100131, Bielefeld D-33501, GermanyFaculty of Physics, Bielefeld University , PO Box 100131, Bielefeld D-33501, Germany; Helmholtz-Zentrum Berlin für Materialien und Energie , Berlin 12489, GermanyThe nature of the phase transition has been studied in MnNi _1− _x Co _x Ge _0.97 Al _0.03 ( x = 0.20–0.50) through magnetization, differential scanning calorimetry and x-ray diffraction measurements; and the associated reversibility in the magnetocaloric effect has been examined. A small amount of Al substitution for Ge can lower the structural phase transition temperature, resulting in a coupled first-order magnetostructural transition (MST) from a ferromagnetic orthorhombic to a paramagnetic hexagonal phase in MnNi _1− _x Co _x Ge _0.97 Al _0.03 . Interestingly, a composition-dependent triple point (TP) has been detected in the studied system, where the first-order MST is split into an additional phase boundary at higher temperature with a second-order transition character. The critical-field-value of the field-induced MST decreases with increasing Co concentration and disappears at the TP ( x = 0.37) resembling most field-sensitive MST among the studied compositions. An increase of the hexagonal lattice parameter a _hex near the TP indicates a lattice softening associated with an enhancement of the vibrational amplitude in the Ni/Co site. The lattice softening leads to a larger field-induced structural entropy change (structural entropy change≫ magnetic entropy change, for this class of materials) with the application of a lower field, which results in a larger reversibility of the low-field entropy change (|Δ S _rev | = 6.9 J kg ^−1 K for Δ μ _0 H = 2 T) at the TP.https://doi.org/10.1088/2515-7655/acf957magnetocaloric effecttriple pointreversible entropy changelattice softening |
| spellingShingle | Tapas Samanta Chris Taake Laila Bondzio Luana Caron Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point JPhys Energy magnetocaloric effect triple point reversible entropy change lattice softening |
| title | Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point |
| title_full | Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point |
| title_fullStr | Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point |
| title_full_unstemmed | Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point |
| title_short | Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point |
| title_sort | entropy change reversibility in mnni1 x co x ge0 97al0 03 near the triple point |
| topic | magnetocaloric effect triple point reversible entropy change lattice softening |
| url | https://doi.org/10.1088/2515-7655/acf957 |
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