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We report a study of the effect of hydrostatic pressure on the magnetocaloric effect in a La0.69Ca0.31MnO3 single crystal. The single crystal exhibits a much larger magnetic entropy change (ΔSm) than the corresponding polycrystalline samples, reaching 5.2 J/kg K and 8.5 J/kg K for a magnetic field variation of 1 T and 5 T, respectively. Under hydrostatic pressure, the peak position of ΔSm significantly moves to higher temperatures due to the shift of the magnetic phase transition, from 213.5 K under ambient pressure up to 236.5 K under a pressure of 1.1 GPa, while the maximum value of ΔSm remains nearly the same. These exceptional results demonstrate that the magnetocaloric effect in magnetic materials with strong spin-lattice coupling can be effectively tuned by pressure. [ABSTRACT FROM AUTHOR]

In order to investigate the magnetic anisotropy of Fe nanowire arrays from microscopic point of view, 57Fe Mosshauer spectra were measured at various magnetic fields along and perpendicular to the nanowire axis, respectively. On the basis of the absorption intensities of the second and the fifth lines of sextet, the orientation of Fe magnetic moments can he detected. It was found that the shape anisotropy dominates the overall magnetic anisotropy in the Fe nanowires. Furthermore, the longitudinal and transverse demagnetizing fields of Fe nanowire, respectively, were deduced from the effective hyperfine field at 57Fe nuclei as a function of applied field. The chain-of-spheres model in conjunction with symmetric fanning mechanism was adopted to interpret the domain structure and the parallel coercivity of magnetic nanowire arrays. [ABSTRACT FROM AUTHOR]

Direct evidence of a field-induced magnetic phase transition in LaFe13-xSix intermetallics with a large magneticaloric effect was provided by 57Fe Mössbauer spectra in externally applied magnetic fields. Moreover, Mössbauer spectra demonstrate that a magnetic structure collinear to the applied field is abruptly achieved in LaFe11.7Si1.3 compound once the ferromagnetic state appears, showing a metamagnetic first-order phase transition. In the case of LaFe11.0Si2.0, the Fe magnetic moments rotate continuously from a random state to the collinear state with increasing applied field, showing that a second-order phase transition is predominant. The different types of phase transformation determine the magnetocaloric effects in response to temperature and field in these two samples. [ABSTRACT FROM AUTHOR]

The local structure of the Fe-doped La[sub 1-x]Ca[sub x]MnO[sub 3] (x=0.00–1.00) compounds has been investigated by means of Mössbauer spectroscopy. [sup 57]Fe Mössbauer spectra provide direct evidence of Jahn–Teller distortion in these manganites. On the basis of the Mössbauer results, the Jahn–Teller coupling was estimated. It is noteworthy that the Ca-concentration dependence of the Jahn–Teller coupling strength is very consistent with the magnetic phase diagram. Our results reveal that Mössbauer spectroscopy cannot only detect the local structural distortion, but also provide a technique to investigate the Jahn–Teller coupling of Fe-doped La[sub 1-x]Ca[sub x]MnO[sub 3] colossal magnetoresistive perovskites. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]