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  • 1
    Electronic Resource
    Electronic Resource
    Dependence of media noise on grain size and intergranular coupling in thin-film media : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5339-5341 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The media noise performance is discussed in connection with grain size and intergranular coupling for the Co85.5Cr10.5Ta4, Co78Cr17Ta5, and Co62.5Ni30Cr7.5 thin-film media fabricated under the ultraclean sputtering process (UC process). It is clarified that the value of S/Nm is quantitatively represented as functions of the value of Hc/Hkgrain and the grain size in every kind of media. The value of signal-to-media noise ratio (S/Nm) increases with the increment in Hc/Hkgrain and also with the decrement in grain size. In the media with grains adequately separated by segregated grain boundaries fabricated by the UC process, grain-size reduction, taking account of the decrease in intergranular magnetostatic coupling, is required to obtain even higher S/Nm values. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361371
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  • 2
    Electronic Resource
    Electronic Resource
    Structure and magnetic moment of α″-Fe16N2 compound films: Effect of Co and H on phase formation (invited) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5564-5569 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to determine the intrinsic value of magnetic moment, σs, of α″-Fe16N2 compound, the magnetic moment of (α″+α′)-Fe16N2 films is discussed in connection with the degree of N site ordering in nitrogen–martensite. To establish the more general relation between Fe–N martensite structure and σs, the Fe–N system is expanded to Fe–Co–N and Fe–H–N systems. As a result, it is found that (1) The existence of completely the same structure as bulk α″ phase was reconfirmed even in the film form by the precise structural analysis using x-ray diffraction, transmission electron microscopy and Mössbauer analysis, (2) Fe–H martensite was synthesized by using sputtering under Ar+H2 atmosphere, (3) Stable formation of α″-(Fe100−XCoX)16N2 (X=10–30) phase through N site ordering by postannealing is proposed to be fairly difficult due to the sudden decrement of the phase decomposition temperature, Tp.d., of α′-(Fe100−XCoX)–N (X=0–30). Tp.d. of α′-(Fe100−XCoX)–N (X=0–30) phase decreases from 200 °C to RT with increasing Co and N contents, and (4) The intrinsic value of saturation magnetization of the α″-Fe16N2 phase is convinced to be no more than 240 emu/g (≈2.4 μB per Fe atom on average) at 300 K. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362244
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure and giant magnetoresistance of Co–Cu granular films fabricated under the extremely clean sputtering process : The 7th joint MMM-intermag conference on magnetism and magnetic materials (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7004-7006 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to clarify the influence of the impurities in the sputtering atmosphere on the microstructure and the giant magnetoresistance (GMR) properties of nanogranular thin films, Co–Cu alloy films were prepared on quartz substrates at room temperature under the different purity of the sputtering atmosphere by changing the base pressure, 10−11 Torr extremely clean process (XC) and 10−7 Torr lower grade process (LG). The correlation between the microstructure and the GMR of films after an annealing procedure is discussed. As results, we found that; (1) A Co-rich phase combined with oxygen was formed at grain boundary in the films as deposited under the LG process; (2) the gradual progress of the grain growth of precipitates with increasing annealing temperature was observed in the XC-processed films, while the coarse grain growth of the matrix phase, resulting in the abrupt change of magnetoresistance occurred in the LG-processed films. We conclude that regulated impurity concentration in the films is an essential parameter to control the precipitation process from the supersaturated solid solution and to realize the desirable microstructure of the nanogranular GMR thin films. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367625
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetic moment of α″-Fe16N2 films (invited) : The 6th joint magnetism and magnetic materials (MMM)−intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6642-6647 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to determine the value of the intrinsic magnetic moment of the α ‘ phase, the films of nitrogen-martensite with various N content were fabricated under various reactive sputtering conditions. The magnetic moment of (α ‘+α')-Fe16N2 films is discussed in connection with the change of the unit-cell volume of the bct structure and the degree of N site ordering in nitrogen-martensite. As a result, it is found that (1) the same structure as bulk α ‘-Fe16N2 is realized in the present films, (2) the saturation magnetization σs of the α' phase increases about 4% with increasing unit-cell volume of the α' phase, (3) the degree of N site ordering from α' to α ‘-Fe16N2 does not much affect σs, and (4) the experimentally obtained maximum value of σs for the (α ‘+α')-Fe16N2 film was 232 emu/g. The intrinsic value of σs in the α ‘ phase (in the perfectly ordered state) is proposed to be no more than 240 emu/g at 300 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358431
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  • 5
    Electronic Resource
    Electronic Resource
    Role of oxygen in the film growth and giant magnetoresistance of Co/Cu multilayers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6308-6313 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to clarify the effect of oxygen in the sputtering atmosphere on the microstructure and giant magnetoresistance, Co/Cu multilayers were fabricated under a sputtering atmosphere into which regulated impurity oxygen gas was introduced. After being pumped down the sputtering chamber to the ultimate pressure (less than 1×10−10 Torr), oxygen was introduced into the chamber until its content in processing Ar gas was about 0.1 ppm to 0.1%. The magnetoresistance (MR) ratio drastically increased from less than 20% to 54% when the content of impurity oxygen was slightly increased from 20 to 80 ppm, then nearly vanished when the content became more than 200 ppm. In the former region where the MR ratio steeply increased, the root mean square roughness of the multilayers decreased from 6.5 to 4.5 Å accompanied by a reduction in grain size as the oxygen content was increased. The partial oxidation of the multilayers is the most probable mechanism by which the flattening of the interfaces in the multilayer can be explained. We conclude that the impurity oxygen in the sputtering atmosphere serves as an obstruction of grain growth in the multilayer, not as a surfactant for the film growth. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1367877
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  • 6
    Electronic Resource
    Electronic Resource
    Enhancement of exchange bias in Mn–Ir/Co–Fe based spin valves with an ultrathin Cu underlayer and in situ Mn–Ir surface modification (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6609-6611 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Enhancement of exchange bias induced at the interface of the antiferromagnetic (AF)/ferromagnetic (F) layers was studied using the bottom "spin-valve films" (SVs) with the Mn–Ir/Co–Fe exchange coupled films. Exchange bias increased using an ultrathin Cu underlayer. Meanwhile, both exchange bias field, Hex, and blocking temperature, TB, increased intensively by heating specimens after depositing Mn–Ir film in a high vacuum. These two enhancement effects worked in an additive. As a result, an unidirectional anisotropy constant, JK, of 0.39 erg/cm2 (Hex of 1.3 kOe) and TB of ∼325 °C were obtained for the bottom SVs with a total thickness of 233 Å including an AF layer of 68 Å Mn74Ir26 and a pinned layer of 20 Å Co90Fe10, where the SVs were field annealed at 320 °C. A microstructural analysis using x-ray diffraction revealed that Hex did not depend on the diffraction intensity from Mn–Ir (111) for the SVs with various underlayers, and no remarkable changes occurred in the microstructure of the SVs with the heating treatment in a vacuum. Therefore, the enhancement effects might result from some changes in the microstructure and/or the morphology of the interface of AF/F layers. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1357146
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  • 7
    Electronic Resource
    Electronic Resource
    Grain size reduction by utilizing a very thin CrW seedlayer and dry-etching process in CoCrTaNiPt longitudinal media (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6860-6862 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To decrease grain size and grain size distribution in CoCr15Ta3.5Ni10Pt5/Cr longitudinal thin film media, a very thin CrW54 seedlayer combined with a dry-etching process were utilized. In the media dry etched after CrW54 deposition, utilization of 1.5 nm CrW54 reduces the grain diameter and σ to 9.4 and 2.2 nm, respectively. By optimizing CrW54 seedlayer thickness and dry-etching process, grain diameter and σ of the magnetic layer can be reduced while maintaining coercivity, longitudinal orientation of magnetic grains, and magnetic interactions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372866
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetic and structural properties of CoCrTaNiPt longitudinal thin-film media (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6866-6868 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of Ni addition on magnetic and structural properties of CoCrTaNiPt/Cr longitudinal media fabricated under the UC process have been investigated. It is found that the addition of Ni up to 13 at. % increases the magnetocrystalline anisotropy field of grain Hkgrain by 10%, and decreases the saturation magnetization Ms by 20%. As a result, coercivity Hc increases by 10%–15% and the ratio of the saturation flux density to anisotropy field 4πMs/Hkgrain decreases by 30%. Further addition of Ni from 13 to 19 at. % results in a decrease of Hc by 7% and a decrease of Hc/Hkgrain from 0.38 to 0.36. This is due to the degraded grain-boundary structure and the increase of the stacking fault density. The addition of Ni up to 13 at. % is effective in increasing Hkgrain and decreasing 4πMs/Hkgrain, while retaining a high Hc/Hkgrain value of about 0.38. As a result, Hc as high as 3.2 kOe is obtained even when using an isotropic NiP/Al substrate. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372868
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  • 9
    Electronic Resource
    Electronic Resource
    Single spin ensemble model for the change of unidirectional anisotropy constant by annealing on polycrystalline ferromagnetic/ antiferromagnetic bilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4957-4959 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A model for the exchange coupled polycrystalline ferromagnetic/antiferromagnetic (F/AF) bilayers is proposed in order to discuss the mechanism of the change of the unidirectional anisotropy constant (JK) of the bilayers by thermal annealing. The AF layer is treated as an aggregation of the AF grains whose magnetic anisotropy axes lay in the film plane with two-dimensionally random distribution. Two stable states concerning the direction of the AF spins are calculated for the AF grain. Determining the populations of the AF grains in each state in thermal equilibrium, total energy of the system is obtained, which provides the magnetization curves and the magnetic torque curves of the F/AF bilayers. The calculated results show the reduction of JK with increasing the equilibrium temperature, which is due to the changes of the probability functions for the respective spin alignments of the AF grain. We conclude that the changes in JK do not necessarily need any changes of the microstructure and the intrinsic physical quantities of the F/AF bilayers. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373214
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic anisotropy in antiferromagnetic layers affecting exchange bias of Ni–Fe/Mn–Ir bilayers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4930-4932 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic anisotropy of antiferromagnetic layers (KAF) was estimated for Ni–Fe 50 Å/Mn–Ir dAF bilayers using Mauri's method (dAFcr=JKs/KAF), where JKs is the saturation value of the unidirectional anisotropy constant (JK). The critical thickness of the antiferromagnetic layers (dAFcr), at which JK took half the value of JKs, was determined from the dependence of JK on dAF. The dAFcr was found to be almost constant (35±2 Å) independent of JKs. Thus, the relation of JKs∝KAF was derived, suggesting that the variation in JKs is due to a change in the value of KAF. JKs, however, was found to vary considerably for various Mn–Ir films possessing an almost identical Ir content, and thus probably the same value of KAF. In addition, studies by x-ray diffraction, transmission electron microscopy, and electron diffraction revealed that the change in JKs was independent of the microstructure and phase of the antiferromagnetic (AF) Mn–Ir films, both of which control KAF. Thus, JKs was found to be independent of KAF contradicting the relation, JKs∝KAF. This contradiction results from the assumption by Mauri that the coupling energy (J) is equal to JKs even in the polycrystalline exchange-coupled bilayers. A model that took account of the distribution of KAF axes of AF grains in the plane of the AF film successfully explained the behavior of JK. JKs was found to change independent of both J and KAF, and furthermore, it has been shown that the dependence of JKs on the sputtering conditions for Mn–Ir films is probably due to the effective temperature of the films during deposition. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373206
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