Author
Satoshi Okamoto
Other affiliations: National Institute for Materials Science
Bio: Satoshi Okamoto is an academic researcher from Tohoku University. The author has contributed to research in topics: Magnetic anisotropy & Magnetization. The author has an hindex of 33, co-authored 216 publications receiving 5574 citations. Previous affiliations of Satoshi Okamoto include National Institute for Materials Science.
Papers published on a yearly basis
Papers
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TL;DR: The magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy is reported, attributing this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase in the Ni45Co5Mn36.7In13.3 single crystal.
Abstract: Large magnetic-field-induced strains1 have been observed in Heusler alloys with a body-centred cubic ordered structure and have been explained by the rearrangement of martensite structural variants due to an external magnetic field1,2,3. These materials have attracted considerable attention as potential magnetic actuator materials. Here we report the magnetic-field-induced shape recovery of a compressively deformed NiCoMnIn alloy. Stresses of over 100 MPa are generated in the material on the application of a magnetic field of 70 kOe; such stress levels are approximately 50 times larger than that generated in a previous ferromagnetic shape-memory alloy4. We observed 3 per cent deformation and almost full recovery of the original shape of the alloy. We attribute this deformation behaviour to a reverse transformation from the antiferromagnetic (or paramagnetic) martensitic to the ferromagnetic parent phase at 298 K in the Ni45Co5Mn36.7In13.3 single crystal.
1,581 citations
TL;DR: In this paper, the magnetic anisotropy of FePt films has been determined with high accuracy by analyzing the magnetization curves obtained from the Hall voltage measurement, implying that the Curie temperature weakly depends on S.
Abstract: Anomalous Hall voltage was measured for FePt ${L1}_{0}$ films having very high magnetic anisotropy. The magnetic anisotropy ${K}_{1}$ and ${K}_{2}$ were determined with high accuracy by analyzing the magnetization curves obtained from the Hall voltage measurement. The saturation magnetization ${M}_{s}$ of the samples with different chemical-order parameter (S) exhibits a different temperature dependence, implying that the Curie temperature weakly depends on S. The first-order anisotropy ${K}_{1}$ gradually increases with S, while the second-order anisotropy ${K}_{2}$ remains almost constant of about $5\ifmmode\times\else\texttimes\fi{}{10}^{6}\mathrm{e}\mathrm{r}\mathrm{g}/\mathrm{c}\mathrm{c}.$ The temperature dependence of ${K}_{1}$ is correlated with S, that is, ${K}_{1}$ with a small S is more temperature dependent than that with a large S. These behaviors are quite similar to the temperature dependence of ${M}_{s}$ with different S, and can be explained by the conventional model based on thermal spin fluctuations. The domain wall energy ${\ensuremath{\sigma}}_{w}$ evaluated by the theoretical analysis of the stripe-domain structure tends to increase linearly with S, in a similar manner as that of ${K}_{1},$ whereas the exchange stiffness constant A of about $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\mathrm{e}\mathrm{r}\mathrm{g}/\mathrm{c}\mathrm{m}$ deduced from ${\ensuremath{\sigma}}_{w}$ and ${K}_{u}{(=K}_{1}{+K}_{2})$ hardly depends on S.
402 citations
TL;DR: In this article, shape memory and magnetic properties of a Ni43Co7Mn39Sn11 Heusler polycrystalline alloy were investigated by differential scanning calorimetry, the sample extraction method, and the three-terminal capacitance method.
Abstract: Shape memory and magnetic properties of a Ni43Co7Mn39Sn11 Heusler polycrystalline alloy were investigated by differential scanning calorimetry, the sample extraction method, and the three-terminal capacitance method. A unique martensitic transformation from the ferromagnetic parent phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced “reverse” transition was confirmed in a high magnetic field. In addition, a large magnetic-field-induced shape recovery strain of about 1.0% was observed to accompany reverse martensitic transformation, and the metamagnetic shape memory effect, which was firstly reported in a Ni45Co5Mn36.7In13.3 Heusler single crystal, was confirmed in a polycrystalline specimen.
357 citations
TL;DR: In this article, a unique martensitic transition from the ferromagnetic austenite phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced reverse transition was confirmed in a high magnetic field.
Abstract: Magnetic and martensitic transition behaviors of a Ni46Mn41In13 Heusler alloy were investigated by differential scanning calorimetry and vibrating sample magnetometry. A unique martensitic transition from the ferromagnetic austenite phase to the antiferromagneticlike martensite phase was detected and magnetic-field-induced “reverse” transition was confirmed in a high magnetic field. In addition, a large positive magnetic entropy change, which reached 13J∕kgK at 9T, was observed to accompany reverse martensitic transition. This alloy shows promise as a metamagnetic shape memory alloy with magnetic-field-induced shape memory effect and as a magnetocaloric material.
244 citations
TL;DR: In this paper, the orbital degree of freedom in the metal-insulator transition in lightly doped manganites has been investigated and it has been shown that the key parameter in the transition is the orbital degrees of freedom of the electrons.
Abstract: A lightly doped manganite ${\mathrm{La}}_{0.88}{\mathrm{Sr}}_{0.12}{\mathrm{MnO}}_{3}$ exhibits a phase transition at ${T}_{\mathrm{OO}}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}145\phantom{\rule{0ex}{0ex}}\mathrm{K}$ from a ferromagnetic metal ( ${T}_{C}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}172\phantom{\rule{0ex}{0ex}}\mathrm{K}$) to a novel ferromagnetic insulator. We identify that the key parameter in the transition is the orbital degree of freedom in ${e}_{g}$ electrons. By utilizing the resonant x-ray scattering, orbital ordering is directly detected below ${T}_{\mathrm{OO}}$, in spite of a significant diminution of the cooperative Jahn-Teller distortion. The experimental features are well described by a theory treating the orbital degree of freedom under strong electron correlation. The present studies uncover a crucial role of the orbital degree of freedom in the metal-insulator transition in lightly doped manganites.
161 citations
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TL;DR: In this paper, a large variety of experiments reviewed in detail here contain results compatible with the theoretical predictions, including phase diagrams of manganite models, the stabilization of the charge/orbital/spin ordered half-doped correlated electronics (CE)-states, the importance of the naively small Heisenberg coupling among localized spins, the setup of accurate mean-field approximations, and the existence of a new temperature scale T∗ where clusters start forming above the Curie temperature, the presence of stripes in the system, and many others.
2,927 citations
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TL;DR: Lipson and Steeple as mentioned in this paper interpreted X-ray powder diffraction patterns and found that powder-diffraction patterns can be represented by a set of 3-dimensional planes.
Abstract: Interpretation of X-ray Powder Diffraction Patterns . By H. Lipson and H. Steeple. Pp. viii + 335 + 3 plates. (Mac-millan: London; St Martins Press: New York, May 1970.) £4.
1,867 citations
IBM1
TL;DR: Heusler compounds as discussed by the authors are a remarkable class of intermetallic materials with 1:1:1 or 2:1-1 composition comprising more than 1500 members, and their properties can easily be predicted by the valence electron count.
1,675 citations
TL;DR: A phenomenological model is established that reveals the parameters essential for such a large adiabatic temperature change ΔT(ad), and it is demonstrated that obstacles to the application of Heusler alloys can be overcome by using the multi-response to different external stimuli and/or fine-tuning the lattice parameters.
Abstract: Magnetic cooling could be a radically different energy solution that could replace conventional vapour compression refrigeration in the future. It is now shown that a Heusler-type magnetocaloric alloy exhibits a remarkable cooling capability due to the effect of a sharp structural transformation at a specific temperature. The finding may be of relevance beyond Heusler alloys and represents an important step towards the implementation of cooling systems based on magnetocaloric materials.
1,233 citations
TL;DR: In this paper, the phase separation phenomenon on various time-scales (from static to dynamic) and the enhanced phase fluctuation with anomalous reduction in the transition temperatures of the competing phases (and hence in the bicritical-point temperature).
Abstract: Colossal magnetoresistance (CMR) phenomena are observed in the perovskite-type hole-doped manganites in which the double-exchange ferromagnetic metal phase and the charge–orbital ordered antiferromagnetic phase compete with each other. The quenched disorder arising from the inherent chemical randomness or the intentional impurity doping may cause major modifications in the electronic phase diagram as well as in the magnetoelectronic properties near the bicritical point that is formed by such a competition of the two phases. One is the phase separation phenomenon on various time-scales (from static to dynamic) and on various length-scales (from glass-like nano to grain-like micron). The other is the enhanced phase fluctuation with anomalous reduction in the transition temperatures of the competing phases (and hence in the bicritical-point temperature). The highly effective suppression of such a phase fluctuation by an external magnetic field is assigned here to the most essential ingredient of the CMR physics. Such profound and dramatic features as appearing in the bicritical region are extensively discussed in this paper with ample examples of the material systems specially designed for this purpose. The unconventional phase-controls over the competing phases in terms of magnetic/electric fields and photo-excitations are also exemplified.
1,166 citations