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Fujita, Akira; Fujieda, Shun; Fukamichi, K.; Mitamura, Hiroyuki; Goto, T.

doi:10.1103/physrevb.65.014410

Cited by 278 publications

(199 citation statements)

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“…Th e paramagnetic to ferromagnetic transition in La -Fe -Si (and Co-doped) compounds is accompanied by a sizeable volume change of about 1 % (ref. 19). Th ere is no change in the crystal symmetry, but the sample isotropically expands as it transforms from the high-temperature paramagnetic to the lowtemperature ferromagnetic phase.…”

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confidence: 99%

Inverse barocaloric effect in the giant magnetocaloric La–Fe–Si–Co compound

et al. 2011

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Application of hydrostatic pressure under adiabatic conditions causes a change in temperature in any substance. This effect is known as the barocaloric effect and the vast majority of materials heat up when adiabatically squeezed, and they cool down when pressure is released (conventional barocaloric effect). There are, however, materials exhibiting an inverse barocaloric effect: they cool when pressure is applied, and they warm when it is released. Materials exhibiting the inverse barocaloric effect are rather uncommon. Here we report an inverse barocaloric effect in the intermetallic compound La-Fe-Co-Si, which is one of the most promising candidates for magnetic refrigeration through its giant magnetocaloric effect. We have found that application of a pressure of only 1 kbar causes a temperature change of about 1.5 K. This value is larger than the magnetocaloric effect in this compound for magnetic fi elds that are available with permanent magnets.

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confidence: 99%

Inverse barocaloric effect in the giant magnetocaloric La–Fe–Si–Co compound

et al. 2011

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“…This would correspond to a 14% decrease of the volume in the PM phase compared to the FM phase whereas the experimentally determined decrease is about 1 to 2%. 5,13,20 In the following we will show that an atomic jump process model 23,24 with different activation energies ∆G 1 and ∆G 2 , as shown in Fig. 2 (c), would be a reasonable origin of the driving force.…”

Section: Resultsmentioning

confidence: 99%

“…An itinerant electron metamagnetic transition can be induced by a magnetic field above T C but below a metamagnetic transition temperature T M . [3][4][5][6] By increasing the silicon content T C increases while T M decreases and the transition becomes less first order until the metamagnetic transition line merges with the magnetic transition line at x ≈ 1.8. 5 For x > 1.8 the magnetic transition is second order with a much smaller MCE and no metamagnetic transition can be found.…”

Section: Introductionmentioning

confidence: 99%

“…In the simplest model, diffusion of the hydrogen atoms would take place from the lower volume PM phase to the higher volume FM phase 16,17 since the ferromagnetic unit cell volume is about 1 to 2% larger while the symmetry of the cubic crystal structure is preserved. 5,19,20 As a result, the T C of the PM regions T C1 decreases while the T C of the FM regions T C2 increases, stabilizing the resulting states and eventually leading to the appearance of two distinctive magnetic phase transitions.…”

Section: Introductionmentioning

confidence: 99%

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The dynamics of spontaneous hydrogen segregation in LaFe13−xSixHy

Baumfeld

Gercsi

Krautz

et al. 2014

Journal of Applied Physics

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By means of time-and temperature-dependent magnetization measurements, we demonstrate that the timescale of hydrogen diffusion in partially-hydrogenated LaFe 13−x Si x H y is of the order of hours, when the material is held at temperatures close to its as-prepared Curie temperature, T C0 . The diffusion constant is estimated to be D ≈ 10 −15 -10 −16 m 2 s −1 at room temperature. We examine the evolution of a magnetically phase-separated state upon annealing for 3 days at a range of temperatures around T C0 , and show that the thermodynamic driving force behind hydrogen diffusion and phase segregation may be attributed to the lower free energy of hydrogen interstitials in the ferromagnetic state relative to the paramagnetic state.

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“…The IEM transition mentioned above is explained in terms of the negative mode-mode coupling of spin fluctuations 10,11) In itinerant-electron metamagnets, the spin fluctuations in the paramagnetic state are strongly enhanced by the exchange interaction, whereas those in the ferromagnetic state are suppressed due to the onset of local magnetic moments. For Fig.…”

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confidence: 99%

Giant Magnetic Entropy Change in Hydrogenated La(Fe0.88Si0.12)13Hy Compounds

et al. 2002

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A magnetic entropy change ∆S M due to the itinerant-electron metamagnetic (IEM) transition was estimated to be −23 J/kg K around the Curie temperature for La (Fe 0.88 Si 0.12 ) 13 in the magnetic field change from 0 to 5 T. In order to control the Curie temperature while keeping such a large value of ∆S M , hydrogen absorption was carried out. La (Fe 0.88 Si 0.12 ) 13 H 1.0 with T C = 274 K shows a large ∆S M due to the IEM transition around room temperature. The adiabatic temperature change ∆T ad from 0 to 2 T is about 7 K, comparable to that of Gd 5 (Ge 0.5 Si 0.5 ) 4 . By changing the hydrogen concentration, the Curie temperature can be controlled from 195 to 336 K. It should be noted that the magnitude of ∆S M is almost the same after hydrogen absorption. Therefore, the hydrogenated La(Fe 0.88 Si 0.12 ) 13 H y compounds are promising magnetic refrigerants working in a wide range of temperature. The first-order magnetic phase transition exhibits a large magnetocaloric effect due to a large magnetic entropy change ∆S M .1, 2) Especially, magnetic refrigerations could be realized when the first-order phase transition is controlled by external magnetic fields. Recently, the target of the temperature range for magnetic refrigerator has been extended up to around room temperature, and many attempts have been made to develop such materials having the first-order magnetic phase transition at relatively high temperatures. 2, 3)We have demonstrated that La(Fe x Si 1−x ) 13 compounds with a high Fe concentration show a first-order ferromagneticparamagnetic phase transition. 4) In addition, the present compounds exhibit an itinerant-electron metamagnetic (IEM) transition above T C .4, 5) Namely, a magnetic-field induced transition from a Pauli paramagnetic to an itinerant ferromagnetic state takes place. An isotropic large volume expansion is followed by the IEM transition due to the onset of local magnetic moment and the magnetovolume effect, therefore, the present compounds have also been investigated from the viewpoint of magnetostrictive materials. 4,5) In order to realize a large volume expansion at room temperature, the Curie temperature was controlled by the hydrogen absorption.6, 7) The hydrogenated La(Fe 0.88 Si 0.12 ) 13 H 1.0 compound has a higher T C close to room temperature and also exhibits the IEM transition above T C .Recently, it has been reported that La(Fe x Si 1−x ) 13 compounds close to the onset of the IEM transition exhibit a large entropy change ∆S M and these results have been discussed in connection with the IEM trnaition. 8, 9) By applying magnetic field, therefore, a large change of the magnetic entropy is expected in a wide range of temperature by changing the hydrogen concentration y in La(Fe 0.88 Si 0.12 ) 13 H y compounds. In the present paper, the influence of hydrogen absorption on the Curie temperature and the magnetic entropy change in La(Fe 0.88 Si 0.12 ) 13 H y compounds and their characteristics are discussed from the viewpoint of magnetic refrigerants.La(Fe 0.88 Si 0.12 ) 13 co...

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Itinerant-electron metamagnetic transition and large magnetovolume effects inLa(FexSi1−x

Cited by 278 publications

References 22 publications

Inverse barocaloric effect in the giant magnetocaloric La–Fe–Si–Co compound

Inverse barocaloric effect in the giant magnetocaloric La–Fe–Si–Co compound

The dynamics of spontaneous hydrogen segregation in LaFe13−xSixHy

Giant Magnetic Entropy Change in Hydrogenated La(Fe<SUB>0.88</SUB>Si<SUB>0.12</SUB>)<SUB>13</SUB>H<SUB>y</SUB> Compounds

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