The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Migaku Takahashi - One of the best experts on this subject based on the ideXlab platform.
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soft x ray magnetic circular dichroism study of mn ir co fe bilayers with giant Exchange Anisotropy
Applied Physics Letters, 2006Co-Authors: Masakiyo Tsunoda, M Naka, Tetsuya Nakamura, S Yoshitaki, Chiharu Mitsumata, Migaku TakahashiAbstract:Soft x-ray magnetic circular dichroism (XMCD) and element-specific magnetic hysteresis (ESMH) measurements were performed in transmission mode on Mn73Ir27 10nm∕Co70Fe30 2nm bilayers with different chemical orderings of the Mn–Ir layer.The unidirectional Anisotropy constant was 0.55erg∕cm2 for the disordered Mn–Ir layer and 1.18erg∕cm2 for the ordered Mn–Ir layer. The XMCD signal of Mn was observed, which means the induced ferromagnetic component of Mn spins through the Exchange coupling at the interface. No vertical offset of the Mn ESMH loops was observed for either the disordered or the ordered bilayers, which means that insignificant uncompensated Mn spin was pinned at the interface to induce Exchange bias on the Co–Fe layer.
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l12 phase formation and giant Exchange Anisotropy in mn3ir co fe bilayers
Journal of Magnetism and Magnetic Materials, 2006Co-Authors: Masakiyo Tsunoda, Ken Ichi Imakita, M Naka, Migaku TakahashiAbstract:Abstract The degree of order S of Mn–Ir layers and the Exchange Anisotropy of Mn–Ir/Co–Fe bilayers were investigated for various chemical compositions of Mn–Ir layers, underlayer materials, and underlayer thicknesses. It was found that: (1) The compositional range over which L1 2 -phase Mn 3 Ir could be formed is 22–32 at% Ir and giant Exchange Anisotropy is obtained in this range. (2) Ru is favorable as an underlayer material for avoiding interdiffusion with the Mn–Ir layer during deposition on the temperature elevated substrate. (3) The underlayer thickness could be reduced to 5 nm while maintaining a giant Exchange Anisotropy in excess of 1 erg/cm 2 .
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thickness dependence of Exchange Anisotropy of polycrystalline mn3ir co fe bilayers
Journal of Applied Physics, 2005Co-Authors: Ken Ichi Imakita, Masakiyo Tsunoda, Migaku TakahashiAbstract:The dependence of Exchange Anisotropy of polycrystalline Mn3Ir∕Co70Fe30 bilayers on the antiferromagnetic layer thickness (dAF) was investigated. The degree of order of a Mn–Ir layer in the examined bilayers was almost constant of 0.45, regardless of dAF. The findings are stated as follows. A maximum unidirectional Anisotropy constant (JK) of 1.3erg∕cm2 is obtained at dAF=10nm. The critical thickness of dAF, where JK becomes half of its maximum value, is less than 5 nm and comparable to that of the bilayer with disordered Mn–Ir. The blocking temperature (TB) is enhanced in several-ten degrees with ordering of the Mn–Ir layer.
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effect of underlayer on formation of l1 sub 2 phase and resultant giant Exchange Anisotropy in mn ir co fe bilayers
IEEE International Magnetics Conference, 2005Co-Authors: Masakiyo Tsunoda, Ken Ichi Imakita, Migaku TakahashiAbstract:The effect of a 5 nm thick Cu underlayer on the formation of Mn/sub 3/Ir (L1/sub 2/) phase is investigated in Mn-Ir/Co-Fe bilayers. The multilayers are deposited on thermally oxidized Si wafers by magnetron sputtering. The microstructure and magnetic properties of the films are examined at room temperature by X-ray diffraction and grazing incident X-ray diffraction, and with a vibrating sample magnetometer, respectively. The unidirectional Anisotropy constant, J/sub K/, is then calculated with the equation of J/sub K/ = M/sub s//spl middot/d/sub F//spl middot/H/sub ex/, where M/sub s//spl middot/d/sub F/ is the areal saturation magnetization of Co-Fe layer, and H/sub ex/ is the Exchange biasing field determined as a shift of the center of MH-loop along the field axis. An enhancement on J/sub K/ is observed with a maximum value of 1.15 erg/cm/sup 2/ at T/sub sub/ = 130/spl deg/C and T/sub a/ = 320/spl deg/C.
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giant Exchange Anisotropy observed in mn ir co fe bilayers containing ordered mn3ir phase
Applied Physics Letters, 2004Co-Authors: Ken Ichi Imakita, Masakiyo Tsunoda, Migaku TakahashiAbstract:Exchange Anisotropy of Mn73Ir27∕Co70Fe30 bilayers fabricated on a 50-nm-thick Cu under layer by changing the substrate temperature (Tsub) during the deposition of Mn–Ir layer was investigated, correlating with the crystallographic structure of Mn–Ir layer. The unidirectional Anisotropy constant (JK) of the bilayers remarkably varied as a function of Tsub. After the thermal annealing of bilayers at 320 °C in a magnetic field of 1 kOe, JK steeply increased from 0.3 to 1.3erg∕cm2, as Tsub was raised from room temperature to 170 °C. The blocking temperature was enhanced from 270 to 360 °C, simultaneously. The JK of 1.3erg∕cm2 is nearly ten times larger than the values reported in Mn–Ir∕Co–Fe bilayers early in the research of them. The x-ray diffraction profiles showed that the ordered Mn3Ir phase was formed in the antiferromagnetic layer with increasing Tsub. From the coincidence of enhancing JK and increasing peak intensity of superlattice diffraction lines, the Mn3Ir phase was suggested to be an origin of t...
Pinaki Sengupta - One of the best experts on this subject based on the ideXlab platform.
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finite temperature phase transition to the m 1 2 plateau phase in the spin 1 2 xxz model on the shastry sutherland lattices
Physical Review B, 2010Co-Authors: Takanori Suzuki, Yusuke Tomita, Naoki Kawashima, Pinaki SenguptaAbstract:We study the finite-temperature transition to the $m=1/2$ magnetization plateau in a model of interacting $S=1/2$ spins with longer-range interactions and strong Exchange Anisotropy on the geometrically frustrated Shastry-Sutherland lattice. This model was shown to capture the qualitative features of the field-induced magnetization plateaus in the rare-earth tetraboride, ${\text{TmB}}_{4}$. Our results show that the transition to the plateau state occurs via two successive transitions with the two-dimensional Ising universality class, when the quantum Exchange interactions are finite, whereas a single phase transition takes place in the purely Ising limit. To better understand these behaviors, we perform Monte Carlo simulations of the classical generalized four-state chiral clock model and compare the phase diagrams of the two models. Finally, we estimate a parameter set that can explain the magnetization curves observed in ${\text{TmB}}_{4}$. The magnetic properties and critical behavior of the finite-temperature transition to the $m=1/2$ plateau state are also discussed.
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finite temperature phase transition to m 1 2 plateau phase in a s 1 2 xxz model on shastry sutherland lattices
Physical Review B, 2010Co-Authors: Takafumi Suzuki, Yusuke Tomita, Pinaki Sengupta, Naoki KawashimaAbstract:We study the finite-temperature transition to the $m=1/2$ magnetization plateau in a model of interacting $S=1/2$ spins with longer range interactions and strong Exchange Anisotropy on the geometrically frustrated Shastry-Sutherland lattice. This model was shown to capture the qualitative features of the field-induced magnetization plateaus in the rare-earth tetraboride, ${\rm TmB_4}$. Our results show that the transition to the plateau state occurs via two successive transitions with the two-dimensional Ising universality class, when the quantum Exchange interactions are finite, whereas a single phase transition takes place in the purely Ising limit. To better understand these behaviors, we perform Monte Carlo simulations of the classical generalized four-state chiral clock model and compare the phase diagrams of the two models. Finally, we estimate a parameter set that can explain the magnetization curves observed in ${\rm TmB_4}$. The magnetic properties and critical behavior of the finite-temperature transition to the $m=1/2$ plateau state are also discussed.
A E Berkowitz - One of the best experts on this subject based on the ideXlab platform.
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Exchange Anisotropy a review
Journal of Magnetism and Magnetic Materials, 1999Co-Authors: A E Berkowitz, K TakanoAbstract:Abstract Exchange Anisotropy refers to the magnetic manifestations of an Exchange coupling at the interface between two different magnetically ordered systems. Of particular current technological interest is the unidirectional Anisotropy, or `Exchange-bias’ field produced in a ferromagnetic film that is coupled to an appropriate antiferromagnetic film. Experimental characterization and theoretical models are discussed for these types of bilayers for a variety of metallic and oxide film couples.
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coo nio superlattices interlayer interactions and Exchange Anisotropy with ni81fe19 invited
Journal of Applied Physics, 1993Co-Authors: M J Carey, A E BerkowitzAbstract:A strong interlayer Exchange interaction is observed in polycrystallineantiferromagnetic CoO‐NiO thin‐film superlattices. This was determined by measuring the Exchange field H e resulting from coupling these superlattices with Ni81Fe19. The temperature above which H e is zero (the blocking temperature) is taken as a measure of the ordering temperature of the superlattice. In CoO‐NiO superlattices with short repeat distances the CoO and NiO layers order at a single temperature that is between the ordering temperatures of bulk CoO and NiO. These ordering temperatures are the same as for Co x Ni1−x O alloy films with the same overall composition. The temperature dependence of H e in some of the superlattice Exchange couples deviates from the linear behavior expected for cubic antiferromagnets. In addition, the Exchange Anisotropy induced by some CoO‐NiO superlattices is greater than that induced by Co x Ni1−x O. The higher H e and nonlinear temperature dependence suggest that the interlayer coupling has a strong effect on the magnetocrystalline Anisotropy of the layers within the superlattice. Thick‐NiO/thin‐CoO/Ni81Fe19trilayers were produced to investigate the thickness dependence of the oxide‐oxide interaction. When the CoO layers are sufficiently thin (≤20 A), the CoO ordering temperature approximates the NiO value, indicating quite strong coupling throughout the CoO layer. The effect of the coupling is much weaker for thicker CoO layers (≥30 A).
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Exchange Anisotropy in coupled films of ni81fe19 with nio and coxni1 xo
Applied Physics Letters, 1992Co-Authors: M J Carey, A E BerkowitzAbstract:Shifted hysteresis loops were used to investigate Exchange Anisotropy in 500 A CoxNi1−xO/300 A Ni81Fe19 polycrystalline bilayer couples. Bilayers of Ni81Fe19 with NiO have a room‐temperature Exchange field, He, of 30 Oe in the as‐deposited state. A maximum in the Exchange field at room temperature was observed near x=0.4, indicating an optimal alloying of the properties of the high Anisotropy CoO and the high Neel temperature NiO. The blocking temperatures of the Exchange couples vary linearly with x, suggesting a linear dependence of the oxide Neel temperature with x.
Naoki Kawashima - One of the best experts on this subject based on the ideXlab platform.
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finite temperature phase transition to the m 1 2 plateau phase in the spin 1 2 xxz model on the shastry sutherland lattices
Physical Review B, 2010Co-Authors: Takanori Suzuki, Yusuke Tomita, Naoki Kawashima, Pinaki SenguptaAbstract:We study the finite-temperature transition to the $m=1/2$ magnetization plateau in a model of interacting $S=1/2$ spins with longer-range interactions and strong Exchange Anisotropy on the geometrically frustrated Shastry-Sutherland lattice. This model was shown to capture the qualitative features of the field-induced magnetization plateaus in the rare-earth tetraboride, ${\text{TmB}}_{4}$. Our results show that the transition to the plateau state occurs via two successive transitions with the two-dimensional Ising universality class, when the quantum Exchange interactions are finite, whereas a single phase transition takes place in the purely Ising limit. To better understand these behaviors, we perform Monte Carlo simulations of the classical generalized four-state chiral clock model and compare the phase diagrams of the two models. Finally, we estimate a parameter set that can explain the magnetization curves observed in ${\text{TmB}}_{4}$. The magnetic properties and critical behavior of the finite-temperature transition to the $m=1/2$ plateau state are also discussed.
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finite temperature phase transition to m 1 2 plateau phase in a s 1 2 xxz model on shastry sutherland lattices
Physical Review B, 2010Co-Authors: Takafumi Suzuki, Yusuke Tomita, Pinaki Sengupta, Naoki KawashimaAbstract:We study the finite-temperature transition to the $m=1/2$ magnetization plateau in a model of interacting $S=1/2$ spins with longer range interactions and strong Exchange Anisotropy on the geometrically frustrated Shastry-Sutherland lattice. This model was shown to capture the qualitative features of the field-induced magnetization plateaus in the rare-earth tetraboride, ${\rm TmB_4}$. Our results show that the transition to the plateau state occurs via two successive transitions with the two-dimensional Ising universality class, when the quantum Exchange interactions are finite, whereas a single phase transition takes place in the purely Ising limit. To better understand these behaviors, we perform Monte Carlo simulations of the classical generalized four-state chiral clock model and compare the phase diagrams of the two models. Finally, we estimate a parameter set that can explain the magnetization curves observed in ${\rm TmB_4}$. The magnetic properties and critical behavior of the finite-temperature transition to the $m=1/2$ plateau state are also discussed.
Masakiyo Tsunoda - One of the best experts on this subject based on the ideXlab platform.
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soft x ray magnetic circular dichroism study of mn ir co fe bilayers with giant Exchange Anisotropy
Applied Physics Letters, 2006Co-Authors: Masakiyo Tsunoda, M Naka, Tetsuya Nakamura, S Yoshitaki, Chiharu Mitsumata, Migaku TakahashiAbstract:Soft x-ray magnetic circular dichroism (XMCD) and element-specific magnetic hysteresis (ESMH) measurements were performed in transmission mode on Mn73Ir27 10nm∕Co70Fe30 2nm bilayers with different chemical orderings of the Mn–Ir layer.The unidirectional Anisotropy constant was 0.55erg∕cm2 for the disordered Mn–Ir layer and 1.18erg∕cm2 for the ordered Mn–Ir layer. The XMCD signal of Mn was observed, which means the induced ferromagnetic component of Mn spins through the Exchange coupling at the interface. No vertical offset of the Mn ESMH loops was observed for either the disordered or the ordered bilayers, which means that insignificant uncompensated Mn spin was pinned at the interface to induce Exchange bias on the Co–Fe layer.
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l12 phase formation and giant Exchange Anisotropy in mn3ir co fe bilayers
Journal of Magnetism and Magnetic Materials, 2006Co-Authors: Masakiyo Tsunoda, Ken Ichi Imakita, M Naka, Migaku TakahashiAbstract:Abstract The degree of order S of Mn–Ir layers and the Exchange Anisotropy of Mn–Ir/Co–Fe bilayers were investigated for various chemical compositions of Mn–Ir layers, underlayer materials, and underlayer thicknesses. It was found that: (1) The compositional range over which L1 2 -phase Mn 3 Ir could be formed is 22–32 at% Ir and giant Exchange Anisotropy is obtained in this range. (2) Ru is favorable as an underlayer material for avoiding interdiffusion with the Mn–Ir layer during deposition on the temperature elevated substrate. (3) The underlayer thickness could be reduced to 5 nm while maintaining a giant Exchange Anisotropy in excess of 1 erg/cm 2 .
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thickness dependence of Exchange Anisotropy of polycrystalline mn3ir co fe bilayers
Journal of Applied Physics, 2005Co-Authors: Ken Ichi Imakita, Masakiyo Tsunoda, Migaku TakahashiAbstract:The dependence of Exchange Anisotropy of polycrystalline Mn3Ir∕Co70Fe30 bilayers on the antiferromagnetic layer thickness (dAF) was investigated. The degree of order of a Mn–Ir layer in the examined bilayers was almost constant of 0.45, regardless of dAF. The findings are stated as follows. A maximum unidirectional Anisotropy constant (JK) of 1.3erg∕cm2 is obtained at dAF=10nm. The critical thickness of dAF, where JK becomes half of its maximum value, is less than 5 nm and comparable to that of the bilayer with disordered Mn–Ir. The blocking temperature (TB) is enhanced in several-ten degrees with ordering of the Mn–Ir layer.
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effect of underlayer on formation of l1 sub 2 phase and resultant giant Exchange Anisotropy in mn ir co fe bilayers
IEEE International Magnetics Conference, 2005Co-Authors: Masakiyo Tsunoda, Ken Ichi Imakita, Migaku TakahashiAbstract:The effect of a 5 nm thick Cu underlayer on the formation of Mn/sub 3/Ir (L1/sub 2/) phase is investigated in Mn-Ir/Co-Fe bilayers. The multilayers are deposited on thermally oxidized Si wafers by magnetron sputtering. The microstructure and magnetic properties of the films are examined at room temperature by X-ray diffraction and grazing incident X-ray diffraction, and with a vibrating sample magnetometer, respectively. The unidirectional Anisotropy constant, J/sub K/, is then calculated with the equation of J/sub K/ = M/sub s//spl middot/d/sub F//spl middot/H/sub ex/, where M/sub s//spl middot/d/sub F/ is the areal saturation magnetization of Co-Fe layer, and H/sub ex/ is the Exchange biasing field determined as a shift of the center of MH-loop along the field axis. An enhancement on J/sub K/ is observed with a maximum value of 1.15 erg/cm/sup 2/ at T/sub sub/ = 130/spl deg/C and T/sub a/ = 320/spl deg/C.
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giant Exchange Anisotropy observed in mn ir co fe bilayers containing ordered mn3ir phase
Applied Physics Letters, 2004Co-Authors: Ken Ichi Imakita, Masakiyo Tsunoda, Migaku TakahashiAbstract:Exchange Anisotropy of Mn73Ir27∕Co70Fe30 bilayers fabricated on a 50-nm-thick Cu under layer by changing the substrate temperature (Tsub) during the deposition of Mn–Ir layer was investigated, correlating with the crystallographic structure of Mn–Ir layer. The unidirectional Anisotropy constant (JK) of the bilayers remarkably varied as a function of Tsub. After the thermal annealing of bilayers at 320 °C in a magnetic field of 1 kOe, JK steeply increased from 0.3 to 1.3erg∕cm2, as Tsub was raised from room temperature to 170 °C. The blocking temperature was enhanced from 270 to 360 °C, simultaneously. The JK of 1.3erg∕cm2 is nearly ten times larger than the values reported in Mn–Ir∕Co–Fe bilayers early in the research of them. The x-ray diffraction profiles showed that the ordered Mn3Ir phase was formed in the antiferromagnetic layer with increasing Tsub. From the coincidence of enhancing JK and increasing peak intensity of superlattice diffraction lines, the Mn3Ir phase was suggested to be an origin of t...
