Approximant crystals of icosahedral Mg–(Ga,Al)–Zn alloys |
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Authors: | K Edagawa N Naito S Takeuchi |
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Institution: | Institute for Solid State Physics, The University of Tokyo , Roppongi, Minato-ku, Tokyo, 106, Japan |
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Abstract: | The zero field cooled (ZFC) and field cooled (FC) low-field magnetic moment m of a dense frozen ferrofluid containing Fe55Co45 particles of size 4.6nm in hexane exhibits irreversibility at temperatures T?T b≈ 30?K. FC in μ 0 H ≤ 1?T gives rise to shifted minor hysteresis loops below T b. At T c≈ 10?K, sharp peaks of m ZFC and of the ac susceptibility χ ′, a kink of the thermoremanent magnetic moment m TRM, a sizeable reduction of the coercive field H c, and the appearance of a spontaneous moment m SFM indicate a phase transition with near mean-field critical behaviour of both m SFM and χ ′ . These features are explained within a core-shell model of nanoparticles, whose strongly disordered shells gradually become blocked below T b, while their soft ferromagnetic cores couple dipolarly and become superferromagnetic (SFM) below T c. |
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Keywords: | Quasicrystal icosahedral phase approximant phase X-ray diffraction projection scheme Mg-Ga-Al-Zn alloy |
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