Mixed magnetism in magnetocaloric materials with first-order and second-order magnetoelastic transitions

Boeije, M.F.J.; Maschek, M.; Miao, Xuefei; Thắng, Nguyễn Văn; Dijk, N.H. van; Brück, E.

doi:10.1088/1361-6463/aa5db9

Cited by 27 publications

(18 citation statements)

References 21 publications

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“…In (Mn,Fe) 2 (Si,P) compounds no crystallographic transition with a symmetry change nor a jump in the volume occur. This is well documented [22,48,49] and confirmed in this study since no global change in the generalized density of phonon states is observed. As a result, a change in the configurational entropy across the magnetic transition may be neglected.…”

Section: A the Impurity Phasesupporting

confidence: 89%

Lattice dynamics across the magnetic transition in(Mn,Fe)1.95(P,Si)

et al. 2018

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The lattice dynamics in MnFe 0.95 Si 0.50 P 0.50 were investigated experimentally using 57 Fe nuclear inelastic scattering and inelastic x-ray scattering across the first-order magnetic transition which occurs close to room temperature. The lattice dynamics characterization was supported by a macroscopic magnetic characterization, an x-ray diffraction study, and a hyperfine interactions characterization using Mössbauer spectroscopy. The Fe specific and the x-ray generalized density of phonon states were obtained both in the ferromagnetic and in the paramagnetic state. A prominent shift, 2 meV at 20 meV, in the x-ray generalized density of phonon states across the first-order magnetic transition, that involves vibrations with essentially Fe character, is revealed corroborated by a change in the local environment quantified in the isomer shift and the quadrupole splitting. Above 35 meV the vibrational modes are practically insensitive to the magnetic transition. The entropy change induced by a 1 T magnetic field across the magnetic transition, ∼10 J/K/kg, is only a fraction of the Fe vibrational entropy change, 62(21) J/K/kg.

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Section: A the Impurity Phasesupporting

confidence: 89%

Lattice dynamics across the magnetic transition in(Mn,Fe)1.95(P,Si)

et al. 2018

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“…However, the strong electronic changes for w = 0 compared to the series of samples that contain B is however not reflected in the magnetic and the structural properties. Strong localization of the electron density in the paramagnetic state of the Fe-site pointing to other Fe atoms and the P/Si atoms indicate bond formation, which leads to a reduced magnetic moment on the Fe site above T C , which has been reported in our previous investigations [19]. Furthermore, our measurements reveal that the electron density changes across T C are more evenly distributed around the Mn-site, locally resembling the behaviour of a free electron gas.…”

Section: B Electron Density Difference Plotssupporting

confidence: 84%

“…In order to maintain a constant sum of all structure factors we multiplied the structure factors by a temperature-dependent correction factor and normalized the data. The same method has been successfully applied in our previous investigations (for more details see [18,19]). Here we investigate the electron density of the 3f and the In order to emphasize the effects originating from the different magnetic atoms, we only consider the local environment close to the 3f and 3g sites and chose different integration boundaries for the layers containing the 3f and 3g sites: the integration along the c-axis in internal coordinates of the unit cell has been performed from z = -0.25 to 0.25 for the Felayer (3f site) and from z = 0.25 to 0.75 for the Mnlayer (3g site).…”

Section: Electronic Structurementioning

confidence: 99%

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Charge redistribution and the magnetoelastic transition across the first-order magnetic transition in (Mn,Fe) 2 (P,Si,B)

et al. 2018

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We used temperature dependent high-resolution x-ray powder diffraction and magnetization measurements to investigate structural, magnetic and electronic degrees of freedom across the ferromagnetic magneto-elastic phase transition in Mn 1 Fe 1 P 0.6-w Si 0.4 B w (w = 0, 0.02, 0.04, 0.06, 0.08). The magnetic transition was gradually tuned from a strong first-order (w = 0) towards a second-order magnetic transition by substituting P by B. Increasing the B content leads to a systematic increase in the magnetic transition temperature and a decrease in thermal hysteresis, which completely vanishes for w = 0.08. Furthermore, the largest changes in lattice parameter across the magnetic transition occur for w = 0, which systematically becomes smaller approaching the samples with w = 0.08. Electron density plots show a strong directional preference of the electronic distribution on the Fe site, which indicates the forming of bonds between Fe atoms and Fe and P/Si in the paramagnetic phase. On the other hand, the Mn-site shows no preferred directions resembling the behaviour of a free electron gas. Due to the low B concentrations (w = 0 -0.08), distortions of the lattice are limited. However, even small amounts of B strongly disturb the overall topology of the electron density across the unit cell. Samples containing B show a strongly reduced variation in the electron density compared to the parent compound without B.

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“…At the border between first-and second-order transitions, one may find a tricritical transition which has no hysteresis while maintaining a large ∆S M . 12,20,[24][25][26][27] In contrast, for systems without magnetostructural first-order transitions, the main strategy for improving ∆S M has been to increase the magnetic moment. [28][29][30] However, there exist several materials such as AlFe 2 B 2 , 31,32 Mn 5 Ge 3 , 33 CrO 2 , 34 MnCoP, 35 and MnB 35,36 which show promising magnetocaloric properties without any known first-order magnetostructural or magnetoelastic transitions.…”

Section: Introductionmentioning

confidence: 99%

Magnetostructural Coupling Drives Magnetocaloric Behavior: The Case of MnB versus FeB

et al. 2019

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Materials with strongly coupled magnetic and structural transitions can display a giant magnetocaloric effect, which is of interest in the design of energy-efficient and environmentally-friendly refrigerators, heat pumps, and thermomagnetic generators. There also exist however, a class of materials with no known magnetostructural transition that nevertheless show remarkable magnetocaloric effects. MnB has been recently suggested as such a compound, displaying a large magnetocaloric effect at its Curie temperature (570 K) showing promise in recovering low-grade waste heat using thermomagnetic generation. In contrast, we show that isostructural FeB displays very similar magnetic ordering characteristics, but is not an effective magnetocaloric. Temperature-and field-dependent diffraction studies reveal dramatic magnetoelastic coupling in MnB, which exists without a magnetostructural transition. No such behavior is seen in FeB. Furthermore, the magnetic transition in MnB is shown to be subtly first-order, albeit with distinct behavior from that displayed by other magnetocalorics with first-order transitions. Density functional theory-based electronic structure calculations point to the magnetoelastic behavior in MnB as arising from a competition between Mn moment formation and B-B bonding.

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Mixed magnetism in magnetocaloric materials with first-order and second-order magnetoelastic transitions

Cited by 27 publications

References 21 publications

Lattice dynamics across the magnetic transition in(Mn,Fe)1.95(P,Si)

Lattice dynamics across the magnetic transition in(Mn,Fe)1.95(P,Si)

Charge redistribution and the magnetoelastic transition across the first-order magnetic transition in (Mn,Fe) 2 (P,Si,B)

Magnetostructural Coupling Drives Magnetocaloric Behavior: The Case of MnB versus FeB

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