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Migaku Takahashi - One of the best experts on this subject based on the ideXlab platform.
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compositional modulated atomic layer stacking and uniaxial Magnetocrystalline Anisotropy of copt alloy sputtered films with close packed plane orientation
Journal of Applied Physics, 2015Co-Authors: Shin Saito, Naoki Nozawa, Shintaro Hinata, Migaku Takahashi, Kazunari Shibuya, Kazuya Hoshino, Satoru AwayaAbstract:An atomic layer stacking structure in hexagonal close packed (hcp) Co100−xPtx alloy films with c-plane sheet texture was directly observed by a high-angle annular dark-field imaging scanning transmission electron microscopy. The analysis of sequential and/or compositional atomic layer stacking structure and uniaxial Magnetocrystalline Anisotropy (Ku = Ku1 + Ku2) revealed that (1) integrated intensity of the superlattice diffraction takes the maximum at x = 20 at. % and shows broadening feature against x for the film fabricated under the substrate temperature (Tsub) of 400 °C. (2) Compositional separation structure in atomic layers is formed for the films fabricated under Tsub = 400 °C. A sequential alternative stacking of atomic layers with different compositions is hardly formed in the film with x = 50 at. %, whereas easily formed in the film with x = 20 at. %. This peculiar atomic layer stacking structure consists of in-plane-disordered Pt-rich and Pt-poor layers, which is completely different from the ...
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effect of co replacement with fe on uniaxial Magnetocrystalline Anisotropy in disordered hcp coptrh alloy films
IEEE Transactions on Magnetics, 2013Co-Authors: Naoki Nozawa, Shin Saito, Shintaro Hinata, Migaku TakahashiAbstract:The effect of replacing Co with Fe in disordered CoPtRh alloy films was investigated with the aim to increase the spin magnetic moment. The addition of Fe into a pure Co film produced a Co98Fe2 film with maximum uniaxial Magnetocrystalline Anisotropy (Ku), because the magnetic moment is increased with the same degree of stacking faults (SFs) induced into the hcp grains as that for a pure Co film. (Co0.98Fe0.02)PtRh films were compared with CoPtRh films with the same Pt and Rh contents, which revealed that: 1) the degree of SFs were increased; 2) the magnetic moment was increased; and 3) Ku was decreased for all compositions in the (Co0.98Fe0.02)PtRh films. In particular, the (Co0.98Fe0.02)PtRh and CoPtRh films with a larger Rh content than Pt have a greater range for increase of the Ku magnitude by enhancement of the magnetic moment with the retention of or further decrease in the degree of SFs.
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large uniaxial Magnetocrystalline Anisotropy for co50pt50 disordered alloy films with hexagonal close packed stacking structure by substituting pt with rh
Journal of Physics D, 2013Co-Authors: Naoki Nozawa, Shin Saito, Shintaro Hinata, Migaku TakahashiAbstract:In order to increase the uniaxial Magnetocrystalline Anisotropy constant (Ku) of a Co50Pt50 film, CoM(M = Pt, Pd, Rh) disordered films are investigated with respect to stacking faults (SFs) in hexagonal-close-packed (hcp) grains. The Co50Rh50 film was revealed to have nearly perfect hcp stacking, while the Co50Pt50 and Co50Pd50 films contain SFs. Therefore, Pt atoms in the Co50Pt50 films were replaced by Rh atoms to enhance Ku by decreasing the density of SFs. The Co50(Pt1−rRhr)50 film with r = 0.5 showed a maximum Ku of nearly 1 × 107 erg cm−3, which is around 10 times larger than that for the Co50Pt50 film.
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giant negative uniaxial Magnetocrystalline Anisotropy of co80ir20 sputtered films with perfect hexagonal close packed and composition modulated atomic layer stacking
Applied Physics Letters, 2013Co-Authors: Naoki Nozawa, Shin Saito, Shintaro Hinata, Takuya Kimura, Kazunari Shibuya, Kazuya Hoshino, Migaku TakahashiAbstract:Co80Ir20 films with negative uniaxial Magnetocrystalline Anisotropy (Ku) are investigated with respect to the regularity of the stacking sequence and atomic site arrangement. Substrate heating at 600 °C enhances the negative Ku of Co80Ir20 to −9.6 × 106 erg/cm3. X-ray diffraction analysis and scanning transmission electron microscopy of the Co80Ir20 film fabricated at 600 °C indicate (1) a near perfect hexagonal-close-packed (hcp) stacking structure and (2) an atomic layered structure that consists of randomly sequenced Ir-rich and Ir-poor layers. These hcp and composition-modulated atomic layer stacking structures are considered to be the reason for the enhancement of the negative Ku.
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uniaxial Magnetocrystalline Anisotropy for c plane oriented co100 xmx m cr mo w film with stacking faults
Journal of Applied Physics, 2009Co-Authors: Shintaro Hinata, Shin Saito, Ryuichi Yanagisawa, Migaku TakahashiAbstract:Stacking faults (SFs) in Co-based alloy grains in a Co100−xMx (M: Cr, Mo, and W) film are evaluated by means of in-plane x-ray diffraction. Moreover, the correlation between SFs and uniaxial Magnetocrystalline Anisotropy Ku is discussed in connection with the spin-orbit interaction. The ratio of the integrated intensities of the (10.0) to (11.0) diffractions corrected by Lorentz and atomic scattering factors has been proposed as an index for SFs in hcp films with a c-plane sheet texture. This ratio is equal to 0.25 for perfect hcp stacking, while it is 0 for perfect fcc specific stacking. It has a one-to-one correspondence with the probability of -A-B-C- atomic-layer stacking Pfcc. Using this index, pure sputtered Co films are found to have a Pfcc of 10%. The addition of only 5 at. % of Mo or W into the Co grains reduces Pfcc to 2%. Ku was found to increase with the addition of material (e.g., Ku was 4.0×106 ergs/cm3 for 5 at. % Mo), although the atomic magnetic moment of Co decreases monotonously. A Pfcc...
Kazuaki Fukamichi - One of the best experts on this subject based on the ideXlab platform.
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Magnetocrystalline Anisotropy in single-crystal Co-Ni-Al ferromagnetic shape-memory alloy
2020Co-Authors: Asaya Fujita, Haruhiko Morito, Ryosuke Kainuma, Kazuaki Fukamichi, K Ishida, Takao Kudo, Katsunari OikawaAbstract:The single-variant state and the Magnetocrystalline Anisotropy in a single crystal Co 41 Ni 32 Al 27 ferromagnetic shape memory alloy (FSMA) have been investigated. After applying compressive stress, the single-variant state was confirmed by optical micrograph and linear thermal expansion measurements. In the heating process for the single-variant martensite phase, the shrinkage of about 7% takes place at the reverse transformation temperature. From the magnetization curves along the c-, a-axes and the [110] M directions in the single-variant state, the c-axis is determined to be the hard axis and the Magnetocrystalline Anisotropy constant in the single crystal Co 41 Ni 32 Al 27 0 martensite phase is evaluated to be 3:2 Â 10 5 J/m 3 at 5 K
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Temperature dependence of Magnetocrystalline Anisotropy constants in the single variant state of L10-type FePt bulk single crystal
Applied Physics Letters, 2006Co-Authors: K. Inoue, K Ishida, H Shima, Asaya Fujita, Katsunari Oikawa, Kazuaki FukamichiAbstract:The temperature dependence of Magnetocrystalline Anisotropy constants and the saturation magnetization in a single variant state have been investigated for L10-type Fe60Pt40 bulk single crystal prepared under compressive stress. The uniaxial Magnetocrystalline Anisotropy constant Ku evaluated from the magnetization curve is 6.9×107ergcm−3 at 5K. The values of the second- and fourth-order Magnetocrystalline Anisotropy constants K1 and K2 at 5K determined by the Sucksmith–Thompson method are 7.4 and 0.13×107ergcm−3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio c∕a due to the thermal expansion.
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lattice axial ratio and large uniaxial Magnetocrystalline Anisotropy in l 1 0 type fepd single crystals prepared under compressive stress
Physical Review B, 2004Co-Authors: H Shima, Kazuaki Fukamichi, K Ishida, K Oikawa, A Fujita, Akimasa SakumaAbstract:$L{1}_{0}$-type FePd single crystals with a high order degree were prepared by ordering under compressive stress. Experimental and theoretical investigations on the relation among the axial ratio, $d$ electron number and Magnetocrystalline Anisotropy energy (MAE) in $L{1}_{0}$-type FePd single crystals have been carried out. In the concentration dependence of the lattice constants, the $a$ axis exhibits a strong dependence, compared with that of the $c$ axis. As a result, the ratio of $c∕a$ decreases with increasing Pd concentration. The uniaxial Magnetocrystalline Anisotropy constant ${K}_{U}$ at the equiatomic composition is evaluated to be $2.1\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $1.7\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The MAE becomes weaker as the ratio of $c∕a$ is apart from unity at higher Pd compositions. The calculated results by the first principles calculations with the LMTO-ASA including the spin-orbit coupling for the MAE of $L{1}_{0}$-type ${\mathrm{Fe}}_{50}{\mathrm{Pd}}_{50}$ are in accord with the present experimental results. The increase in the $d$ electron number due to the increase of the Pd concentration facilitates the decrease of the MAE, cooperating with the decrease in the axial ratio $c∕a$.
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Magnetocrystalline Anisotropy in single crystal co ni al ferromagnetic shape memory alloy
Applied Physics Letters, 2002Co-Authors: Haruhiko Morito, Ryosuke Kainuma, Kazuaki Fukamichi, Koichi OikawaAbstract:The Magnetocrystalline Anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the Magnetocrystalline Anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.The Magnetocrystalline Anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the Magnetocrystalline Anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.
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Magnetocrystalline Anisotropy in single crystal co ni al ferromagnetic shape memory alloy
Applied Physics Letters, 2002Co-Authors: Haruhiko Morito, Ryosuke Kainuma, Kazuaki Fukamichi, K Ishida, Koichi OikawaAbstract:The Magnetocrystalline Anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the Magnetocrystalline Anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.
K Ishida - One of the best experts on this subject based on the ideXlab platform.
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Magnetocrystalline Anisotropy in single-crystal Co-Ni-Al ferromagnetic shape-memory alloy
2020Co-Authors: Asaya Fujita, Haruhiko Morito, Ryosuke Kainuma, Kazuaki Fukamichi, K Ishida, Takao Kudo, Katsunari OikawaAbstract:The single-variant state and the Magnetocrystalline Anisotropy in a single crystal Co 41 Ni 32 Al 27 ferromagnetic shape memory alloy (FSMA) have been investigated. After applying compressive stress, the single-variant state was confirmed by optical micrograph and linear thermal expansion measurements. In the heating process for the single-variant martensite phase, the shrinkage of about 7% takes place at the reverse transformation temperature. From the magnetization curves along the c-, a-axes and the [110] M directions in the single-variant state, the c-axis is determined to be the hard axis and the Magnetocrystalline Anisotropy constant in the single crystal Co 41 Ni 32 Al 27 0 martensite phase is evaluated to be 3:2 Â 10 5 J/m 3 at 5 K
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Temperature dependence of Magnetocrystalline Anisotropy constants in the single variant state of L10-type FePt bulk single crystal
Applied Physics Letters, 2006Co-Authors: K. Inoue, K Ishida, H Shima, Asaya Fujita, Katsunari Oikawa, Kazuaki FukamichiAbstract:The temperature dependence of Magnetocrystalline Anisotropy constants and the saturation magnetization in a single variant state have been investigated for L10-type Fe60Pt40 bulk single crystal prepared under compressive stress. The uniaxial Magnetocrystalline Anisotropy constant Ku evaluated from the magnetization curve is 6.9×107ergcm−3 at 5K. The values of the second- and fourth-order Magnetocrystalline Anisotropy constants K1 and K2 at 5K determined by the Sucksmith–Thompson method are 7.4 and 0.13×107ergcm−3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio c∕a due to the thermal expansion.
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lattice axial ratio and large uniaxial Magnetocrystalline Anisotropy in l 1 0 type fepd single crystals prepared under compressive stress
Physical Review B, 2004Co-Authors: H Shima, Kazuaki Fukamichi, K Ishida, K Oikawa, A Fujita, Akimasa SakumaAbstract:$L{1}_{0}$-type FePd single crystals with a high order degree were prepared by ordering under compressive stress. Experimental and theoretical investigations on the relation among the axial ratio, $d$ electron number and Magnetocrystalline Anisotropy energy (MAE) in $L{1}_{0}$-type FePd single crystals have been carried out. In the concentration dependence of the lattice constants, the $a$ axis exhibits a strong dependence, compared with that of the $c$ axis. As a result, the ratio of $c∕a$ decreases with increasing Pd concentration. The uniaxial Magnetocrystalline Anisotropy constant ${K}_{U}$ at the equiatomic composition is evaluated to be $2.1\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and $1.7\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}\mathrm{erg}∕{\mathrm{cm}}^{3}$ at $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The MAE becomes weaker as the ratio of $c∕a$ is apart from unity at higher Pd compositions. The calculated results by the first principles calculations with the LMTO-ASA including the spin-orbit coupling for the MAE of $L{1}_{0}$-type ${\mathrm{Fe}}_{50}{\mathrm{Pd}}_{50}$ are in accord with the present experimental results. The increase in the $d$ electron number due to the increase of the Pd concentration facilitates the decrease of the MAE, cooperating with the decrease in the axial ratio $c∕a$.
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Magnetocrystalline Anisotropy in single crystal co ni al ferromagnetic shape memory alloy
Applied Physics Letters, 2002Co-Authors: Haruhiko Morito, Ryosuke Kainuma, Kazuaki Fukamichi, K Ishida, Koichi OikawaAbstract:The Magnetocrystalline Anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the Magnetocrystalline Anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.
Koichi Oikawa - One of the best experts on this subject based on the ideXlab platform.
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Magnetocrystalline Anisotropy in single crystal co ni al ferromagnetic shape memory alloy
Applied Physics Letters, 2002Co-Authors: Haruhiko Morito, Ryosuke Kainuma, Kazuaki Fukamichi, Koichi OikawaAbstract:The Magnetocrystalline Anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the Magnetocrystalline Anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.The Magnetocrystalline Anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the Magnetocrystalline Anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.
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Magnetocrystalline Anisotropy in single crystal co ni al ferromagnetic shape memory alloy
Applied Physics Letters, 2002Co-Authors: Haruhiko Morito, Ryosuke Kainuma, Kazuaki Fukamichi, K Ishida, Koichi OikawaAbstract:The Magnetocrystalline Anisotropy in a single-crystal Co37Ni34Al29 ferromagnetic shape-memory alloy has been investigated. The prestrain was applied to the parent phase in order to nucleate the specific variant in the sample cooled down through the martensitic transformation temperature. The applied magnetic field facilitates the growth of variants parallel to the applied magnetic field in analogy with the prestrain. From these results of selective nucleation of variants, the Magnetocrystalline Anisotropy energy in the single crystal Co37Ni34Al29 β′ martensite phase is estimated to be 3.9×106 erg/cm3. In the single crystal, the observed magnitude of the reversible magnetic-field-induced strains is 0.06%.
Arthur J Freeman - One of the best experts on this subject based on the ideXlab platform.
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role of an interfacial feo layer in the electric field driven switching of Magnetocrystalline Anisotropy at the fe mgo interface
Physical Review B, 2010Co-Authors: Kohji Nakamura, Toru Akiyama, Tomonori Ito, M Weinert, Arthur J FreemanAbstract:The electric-field-induced switching of Magnetocrystalline Anisotropy (MCA) between in-plane and out-of-plane orientations is investigated by first-principles calculations for the prototypical Fe on MgO(001) system. Our results predict that an ideal abrupt Fe/MgO interface gives rise to a large out-of-plane MCA due to weak Fe-O hybridization at the interface, but the MCA switching by an applied electric field is found to be difficult to achieve. Instead, the existence of an interfacial FeO layer plays a key role in demonstrating the MCA switching that accompanies an electric-field-induced displacement of Fe atoms on the interfacial FeO layer.
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giant modification of the Magnetocrystalline Anisotropy in transition metal monolayers by an external electric field
Physical Review Letters, 2009Co-Authors: K Nakamura, Riki Shimabukuro, Toru Akiyama, Tomonori Ito, Yuji Fujiwara, Arthur J FreemanAbstract:Controlling and designing quantum magnetic properties by an external electric field is a key challenge in modern magnetic physics. Here, from first principles, the effects of an external electric field on the Magnetocrystalline Anisotropy (MCA) in ferromagnetic transition-metal monolayers are demonstrated which show that the MCA in an Fe(001) monolayer [but not in Co(001) and Ni(001) monolayers] can be controlled by the electric field through a change in band structure, in which small components of the p orbitals near the Fermi level, which are coupled to the d states by the electric field, play a key role. This prediction obtained opens a way to control the MCA by the electric field and invites experiments.
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torque method for the theoretical determination of Magnetocrystalline Anisotropy
Physical Review B, 1996Co-Authors: Xindong Wang, Ding Sheng Wang, Arthur J FreemanAbstract:We propose a torque method for the theoretical determination of the Magnetocrystalline Anisotropy (MCA) energy for systems with uniaxial symmetry. While the dependence of the total energy on the angle between the magnetization and the normal axis (\ensuremath{\theta}) can be expressed as E(\ensuremath{\theta})=${\mathit{E}}_{0}$+${\mathit{K}}_{2}$${\mathrm{sin}}^{2}$(\ensuremath{\theta})+${\mathit{K}}_{4}$${\mathrm{sin}}^{4}$(\ensuremath{\theta}), we show that the MCA energy [defined as ${\mathit{E}}_{\mathrm{MCA}}$=E(\ensuremath{\theta}=90\ifmmode^\circ\else\textdegree\fi{})-E(\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{})=${\mathit{K}}_{2}$+${\mathit{K}}_{4}$] can be easily evaluated through the expectation value of the angular derivative of the spin-orbit coupling Hamiltonian (torque) at an angle of \ensuremath{\theta}=${45}^{\mathit{o}}$. Unlike other procedures, the proposed method is independent of the validity of the MCA force theorem, or of the absolute accuracy of two total energy calculations. Calculated MCA energies for the free Fe monolayer with different lattice constants are analyzed and compared with results of other ab initio calculations, especially those obtained with our previously reported state tracking method. \textcopyright{} 1996 The American Physical Society.
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first principles theory of surface Magnetocrystalline Anisotropy and the diatomic pair model
Physical Review B, 1993Co-Authors: Ding Sheng Wang, Arthur J FreemanAbstract:The state-tracking method proposed recently is employed for the first-principles determination of the Magnetocrystalline-Anisotropy (MCA) energy. A close relationship of the MCA energy to the band structure is found for transition-metal monolayers that show the change of sign of the MCA with respect to the band filling (atomic species) to be determined mainly by the spin-orbit coupling within the spin-down bands. The Fe monolayer with the \ensuremath{\pi}-bonding band as the highest occupied band exhibits positive MCA (easy axis along the layer normal). However, the effect of strain on the MCA of the Fe monolayer demonstrates the effect of the spin-orbit coupling between opposite-spin states. A model for the electronic origin of the magnetic Anisotropy of this two-dimensional system is presented that explains the first-principles MCA results for iron and cobalt monolayers on the basis of the bonding character between two d atoms, the band broadening due to increase in coordination, and geometry (symmetry).