The itinerant-electron metamagnetic ͑IEM͒ transition and magnetocaloric effects ͑MCE's͒ in the La(Fe x Si 1Ϫx) 13 and La(Fe x Si 1Ϫx) 13 H y compounds have been investigated. The La(Fe x Si 1Ϫx) 13 compounds exhibit large values of both the isothermal entropy change ⌬S m and the adiabatic temperature change ⌬T ad around the Curie temperature T C in relatively low magnetic fields. Such large MCE's are explained by a large magnetization change at T C and a strong temperature dependence of the critical field B C for the IEM transition. By hydrogen absorption into the compounds, T C is increased up to about 330 K, keeping the metamagnetic transition properties. Accordingly, the extension of the working temperature range having the large MCE's in relatively low magnetic fields is demonstrated by controlling y in the La(Fe x Si 1Ϫx) 13 H y compounds. The correlation between the increase of T C and the large MCE's in the La(Fe x Si 1Ϫx) 13 H y compounds is discussed by taking the magnetovolume effects into consideration.

The magnetocaloric effect (MCE) originated from the itinerant-electron metamagnetic transition for La(FexSi1−x)13 compounds has been investigated. With increasing Fe concentration, the MCE is enhanced and both the isothermal magnetic entropy change ΔSm and the adiabatic temperature change ΔTad for the compound with x=0.90 are −28 J/kg K and 8.1 K, respectively, by changing the magnetic field from 0 to 2 T. Similar large MCE values are achieved around room temperature by controlling the Curie temperature by means of hydrogen absorption. Consequently, La(FexSi1−x)13 compounds are promising as magnetic refrigerant materials working in relatively low magnetic fields.

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La(Fe x Si 1−x ) 13 compounds exhibit an itinerant-electron metamagnetic (IEM) transition above Curie temperature TC. The IEM transition in the compound with x=0.88 is accompanied by a giant volume change. From a practical viewpoint, TC was controlled by hydrogen absorption in order to obtain such a giant volume magnetostriction at room temperature. For the La(Fe0.88Si0.12)13H1.0 compound, the IEM transition occurs above TC=278 K, and a significant isotropic linear magnetostriction of about 0.3% at 7 T is induced in the vicinity of room temperature. This large magnetostriction is attributed to the giant volume magnetostriction of about 1% by the IEM transition.

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La(Fe x Si 1−x ) 13 and their hydrides exhibit large magnetocaloric effects due to the itinerant-electron metamagnetic transitions in a wide temperature range covering room temperature. Thermal conductivity and diffusivity of La(Fe0.88Si0.12)13 and La(Fe0.88Si0.12)13H1.0 have been investigated, together with those of other candidates for magnetic refrigerants working in the vicinity of room temperature such as Gd, Gd5Si2Ge2 and MnAs. The thermal conductivity in the vicinity of room temperature for La(Fe0.88Si0.12)13H1.0 is larger than that for Gd5Si2Ge2 and MnAs, and almost identical to that for Gd. Furthermore, the thermal diffusivity in the vicinity of room temperature for La(Fe0.88Si0.12)13H1.0 is as large as that for Gd and Gd5Si2Ge2, and larger than that for MnAs. Consequently, La(FexSi1−x)13 and their hydrides are promising as the magnetic refrigerants from the standpoint of thermal transport properties.

Inorganic chemistry Z 0100 Isotropic Giant Linear Magnetostriction and Large Magnetocaloric Effects in La(FexSi1-x)13 Itinerant-Electron Metamagnetic Compounds and Their Hydrides-[48 refs.]. -(FUJITA, A.; FUJIEDA, S.; FUKAMICHI, K.; Met., Mater. Processes 15 (2003) 3-4, 273-296; Dep. Mater. Sci., Grad. Sch. Eng., Tohoku Univ., Sendai 980, Japan; Eng.) -Schramke 35-243

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