Author
Osamu Kitakami
Other affiliations: Nagoya University, Hitachi
Bio: Osamu Kitakami is an academic researcher from Tohoku University. The author has contributed to research in topics: Magnetic anisotropy & Magnetization. The author has an hindex of 38, co-authored 307 publications receiving 7456 citations. Previous affiliations of Osamu Kitakami include Nagoya University & Hitachi.
Topics: Magnetic anisotropy, Magnetization, Coercivity, Thin film, Anisotropy
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 size dependence of the crystal phase of the Co fine particles was investigated, and it was shown that the stabilization of crystal phase is the intrinsic effect caused by the small dimensionality of fine particles.
Abstract: We have synthesized Co fine particles with the average diameter $(D)$ of less than 500 \AA{} by sputtering Co in a somewhat high inert-gas pressure. It has been found that there is a close relationship between the particle size and the crystal phase; that is, pure fcc (\ensuremath{\beta}) phase for $Dl~200\AA{},$ a mixture of hcp (\ensuremath{\alpha}) and \ensuremath{\beta} phases for $D\ensuremath{\sim}300\AA{},$ and \ensuremath{\alpha} phase with inclusion of a very small amount of \ensuremath{\beta} phase for $Dg~400\AA{}.$ Precise structural characterizations have revealed that the \ensuremath{\beta} particles are multiply twinned icosahedrons and the \ensuremath{\alpha} particles are perfect single crystals with external shape of a Wulff polyhedron. In order to explain the size effect on the crystal phase of Co fine particles, we have performed theoretical calculations for total free energies of an \ensuremath{\alpha} single crystal, a \ensuremath{\beta} single crystal, and a multiply twinned \ensuremath{\beta} icosahedron. The present calculations well explain the size dependence of the crystal phase of the Co fine particles, and have revealed that the stabilization of \ensuremath{\beta} phase, confirmed by previous studies, is the intrinsic effect caused by the small dimensionality of fine particles. Moreover, the phase transformations that occurred in annealing experiments can also be explained by the theory.
452 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
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TL;DR: A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements that arises through the quantum mechanical phenomenon of exchange.
Abstract: A ferroelectric crystal exhibits a stable and switchable electrical polarization that is manifested in the form of cooperative atomic displacements. A ferromagnetic crystal exhibits a stable and switchable magnetization that arises through the quantum mechanical phenomenon of exchange. There are very few 'multiferroic' materials that exhibit both of these properties, but the 'magnetoelectric' coupling of magnetic and electrical properties is a more general and widespread phenomenon. Although work in this area can be traced back to pioneering research in the 1950s and 1960s, there has been a recent resurgence of interest driven by long-term technological aspirations.
6,813 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
TL;DR: The most important members of the hexaferrite family are shown below, where Me = a small 2+ ion such as cobalt, nickel, or zinc, and Ba can be substituted by Sr: • M-type ferrites, such as BaFe12O19 (BaM or barium ferrite), SrFe 12O19(SrM or strontium ferite), and cobalt-titanium substituted M ferrite, Sr- or BaFe 12−2xCoxTixO19, or CoTiM as discussed by the authors.
1,855 citations
TL;DR: The phenomenology of exchange bias and related effects in nanostructures is reviewed in this paper, where the main applications of exchange biased nanostructure are summarized and the implications of the nanometer dimensions on some of the existing exchange bias theories are briefly discussed.
1,721 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