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  • 1
    Electronic Resource
    Electronic Resource
    The absence of giant magnetoresistance on antiferromagnetically coupled NiFe/Cr multilayers : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 5518-5520 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To further investigate the relationship between the giant magnetoresistance (GMR), anisotropic magnetoresistance (AMR), and antiferromagnetic (AFM) coupling found in magnetic multilayers we have deposited NiFe/Cr multilayers onto rectangular Corning 7059 glass substrates at ambient temperatures. Uniaxial anisotropy was induced by applying a 90 Oe field along the length of the substrate strips during deposition and in all cases a 50–100-A(ring)-thick Cr underlayer was used. For Cr interfilms 9–12-A(ring) thick, the multilayers were found to have hard axis saturation fields of 90–200 Oe and easy axis hysteresis loops which exhibit a complex behavior dependent on whether the multilayer is composed of an even or an odd number of NiFe films. Both of these effects result from AFM coupling of the NiFe films. The magnetoresistive (MR) behavior was also found to be complex and dependent on the number of NiFe films in the multilayer. A theoretical model based on coherent rotation and including AFM coupling between the NiFe films has been developed and both the hysteresis loops and MR of the multilayers calculated. From these calculations it has been found that, despite the existence of AFM coupling, the experimentally observed magnetoresistive behavior can be described using only AMR. Thus the existence of AFM coupling does not result in GMR NiFe/Cr multilayers. This is discussed in terms of spin filtering at the multilayer interfaces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353688
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  • 2
    Electronic Resource
    Electronic Resource
    First principles study of direct exchange coupling between the grains in NiMn antiferromagnets (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7940-7942 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Exchange coupling between antiferromagnetic regions of tetragonal NiMn through a separation at a boundary was evaluated by first principles calculation to study the coupling between antiferromagnetic grains. It was assumed that the crystallographic orientation was assumed not to change across the boundary. The layer version of the Korringa–Kohn–Rostoker method was employed to calculate the total energy of the coupled system. The exchange coupling strength was estimated as the total energy difference between the two spin configurations of the two body system, parallel and antiparallel to each other. For the grains without any atomic lattice shift parallel to the plane (100) across the boundary, it was found that the coupling strength decreases more rapidly than that for ferromagnetic hexagonal cobalt with the increase of the separation and that it changes its sign at a separation length of a little greater than a half of the lattice constant. For the case with a boundary across which the lattice shifts by an atomic distance diagonally, the exchange coupling is reduced to about 1/3 of the original value and decreases rather slowly with the increase of the separation compared to the previous case. Those results are consistent with our previous report which predicted the existence of a weak exchange coupling between the grains in an antiferromagnetic polycrystalline layer based on the analysis of a characteristic feature often observed in torque curves for ferro/antiferromagnetic coupled layer systems. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1371945
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  • 3
    Electronic Resource
    Electronic Resource
    Biquadratic coupling effect on magnetoresistance response curves of spin valves with a synthetic antiferromagnet (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6814-6816 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both normal and inverse magnetoresistance (MR) response curves were observed for synthetic spin valves with the structure of Si(100)/Ru/Co(t1)/Ru(0.7 nm)/Co(t2)/Cu(3 nm)/Co(t3)/Ru. Under the assumption of a coherent rotation of the magnetization in the three Co layers, the hysteresis loops, magnetization response, and MR response curves were calculated as a function of the parameters of the system. The parameters include antiferromagnetic coupling of Co(t1) and Co(t2) through Ru layer, a weak ferromagnetic coupling of Co(t2) and Co(t3) through Cu spacer, giant magnetoresistance of the Co/Cu/Co and Co/Ru/Co systems, and AMR contribution of each Co layer. The uniaxial anisotropy of each Co layer and a distribution of the coupling strength of Co(t1)/Ru/Co(t2) were also included. To fit the experimental data well, it was necessary to include a biquadratic coupling in the Co(t1)/Ru/Co(t2) trilayer. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1360679
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  • 4
    Electronic Resource
    Electronic Resource
    Reconstruction of in-plane magnetization distributions from magnetic force microscope images (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7230-7232 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-step method is proposed for reconstructing the in-plane magnetization distribution from a magnetic force microscope (MFM) image. The magnetization distribution is initialized using some assumptions based on our knowledge about domain structures and MFM contrast mechanisms. Then the high-energy moment configurations, which are initialized based on linear variation assumption, are relaxed by performing a micromagnetic calculation using experimentally measured magnetic parameters. A section of a 360° wall in a NiFe/NiO bilayer has been selected to illustrate the reconstruction procedures. It is shown that the method is effective in revealing the wall structure related to the MFM contrast. This method avoids problems caused by noise and nonunique solutions of the micromagnetic equations. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1355338
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  • 5
    Electronic Resource
    Electronic Resource
    Rotational hysteresis of torque curves in polycrystalline ferro/antiferromagnetic systems (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 7546-7548 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Rotational hysteresis of ferromagnetic (F)/antiferromagnetic (AF) exchange coupled systems was studied by using NiFe/IrMn, NiFe/FeMn, and NiFe/NiMn samples sputter deposited under almost the same conditions, although the sample of NiFe/NiMn was annealed later to obtain the antiferromagnetic phase for the NiMn layer. The rotational hysteresis of each sample exhibited quite a different feature from each other, especially in the rotational hysteresis–magnetization angle curves. The NiFe/IrMn bilayer showed a dip at around the antiparallel direction to the applied field direction during sample preparation (pinning direction), while the NiFe/NiMn bilayer exhibited a large peak in that direction. The NiFe/FeMn bilayer did not show any noticeable structure in the rotational hysteresis–magnetization curve. Based on the analysis of those data done by using the model recently proposed by the authors, the following was inferred: (1) The distribution of the anisotropy easy axes of IrMn of the NiFe/IrMn bilayer grains is limited in some range of angles around the pinning direction. Some direct exchange coupling exists between the IrMn grains. (2) The distribution of the anisotropy easy axes of FeMn grains of the NiFe/FeMn bilayer is almost random and the direct exchange coupling between the FeMn grains is negligible. (3) In the NiFe/NiMn bilayer, substantial strength of direct exchange coupling exists between some of the grains which switch and the ones which do not switch with the rotation of the magnetization of the NiFe layer, although the volume fraction of the former is much smaller than the latter. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1358833
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  • 6
    Electronic Resource
    Electronic Resource
    Spin fanning configurations in antiferromagnetic layers with a uniaxial anisotropy and torque transfer characteristics from top to bottom spins (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 4940-4942 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spin configurations along the thickness direction generated in antiferromagnetic (AF) layers with an in-plane uniaxial anisotropy have been calculated by numerical method. It is confirmed that when the bottom-surface anisotropy energy constant is less than 1/4 of 180°-wall energy density, σw, a sudden change or switch of the spin configuration occurs at a critical angle of the top spins when the AF-layer thickness, t, is greater than a critical value, tc. This means that no hysteresis occurs with a rotation of the top spin for t〈tc. Spin configurations with a folded or periodic structure which Néel discussed have been revealed to be unstable without microscopic defects or irregularities which pin the spin angle at some depth from the top surface. It is found that when the bottom-surface anisotropy is lower than 1/4σw, the torque sustainable by the top-surface spins does not exceed 1/2σw. It is also found that the effect of top-spin rotation penetrates substantially down as deeply as a few times the 180°-wall thickness. The effect of the AF-easy axis tilting out of the plane has also been studied. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370052
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical and numerical model for estimating unknown magnetic parameters in studying ferromagnetic and antiferromagnetic coupled films (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 6202-6204 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new method of estimating unknown magnetic parameters for coupled thin films of ferromagnetic and antiferromagnetic materials is introduced. It combines convenient torque and spin angle measurements with strength of mathematical models and numerical techniques. Description of this approach is outlined and test results for several simulated examples are presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370221
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  • 8
    Electronic Resource
    Electronic Resource
    Training effect of exchange biased iron–oxide/ferromagnet systems (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6910-6912 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Substantial training effect in hysteresis loops was observed in ferromagnet (F)–antiferromagnet (AF) exchange coupled systems of the structure, Si(100)/iron–oxide(tAF)/F layer (5 nm)/Ta(10 nm), prepared by magnetron sputtering. The exchange bias field and the coercivity decrease with increasing number of loop cycles. The initially asymmetric hysteresis loop becomes more symmetric as the number of loop cycles increases. The effect is more prominent in the descending curve starting from the saturation in the positive (parallel to the pinned direction) direction than in the ascending curve of the hysteresis loop. The value of the ascending curve switching field |Hsw+| is rather unchanged while the switching field |Hsw−| in the descending curve decreases drastically with repeated hysteresis loop cycling as was observed in some CoO/Co and NiO/NiFe systems. Those phenomena can be interpreted by a modification of the extended model of Fulcomer and Charap's: the essential modification being the introduction of positive and negative exchange coupling between AF grains. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1360682
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  • 9
    Electronic Resource
    Electronic Resource
    Disorder dependence of the magnetic moment of the half-metallic ferromagnet NiMnSb from first principles (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5870-5871 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using half-metallic ferromagnets in spin-dependent devices, like spin valves and ferromagnetic tunnel junctions, is expected to increase the device performance. However, using the half-metallic ferromagnet NiMnSb in such devices led to much less than ideal results. One of the possible sources for this behavior is atomic disorder. First-principles calculations of the influence of atomic disorder on the electronic structure of NiMnSb underline the sensitivity of half-metallic properties in NiMnSb to atomic disorder. In this article, we report on the disorder dependence of the total magnetic moment calculated by applying the layer Korringa–Kohn–Rostoker method in conjunction with the coherent potential approximation. We consider the following types of disorder: (1) intermixing of Ni and Mn, (2) partial occupancy of a normally vacant lattice site by Ni and Mn, and (3) partial occupancy of this site by Mn and Sb. In all cases the composition is kept stoichiometric. All three types of disorder decrease the moment monotonically with increasing disorder levels. For the experimentally seen disorder of 5% Mn and 5% Sb on the normally vacant lattice site, the total moment is decreased by 4.1%. The results suggest that precise measurement of the saturation magnetization of NiMnSb thin films can give information on the disorder. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372550
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  • 10
    Electronic Resource
    Electronic Resource
    Optical interference in magneto-optic Kerr-effect measurements of magnetic multilayers (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 1658-1662 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hysteresis loops of exchange-biased permalloy/Fe50Mn50/permalloy trilayers on glass were measured as a function of Fe50Mn50 and permalloy thicknesses with the longitudinal Kerr effect employing a coherent light source. Kerr signals originate from both permalloy layers and give a superposition of hysteresis loops. In vibrating sample magnetometer or looptracer measurements the contribution of a particular layer to a major hysteresis loop cannot be identified. With the Kerr setup presented it is possible to identify the contribution of each layer individually, since the finite optical path through the trilayer gives rise to optical attenuation and interference. For an increasing total thickness of the trilayer, the signal of the buried permalloy layer will become weaker due to attenuation. Kerr measurements of trilayers up to 40 nm show a superposition of two equally oriented loops. Major loops for trilayers of thickness greater than 40 nm show a superposition of two oppositely oriented hysteresis loops. The transition is dependent only on the total thickness of the trilayer, rather than the thickness of each individual layer. This unusual effect can be explained by the phase difference of the two Kerr signals. Additional measurements performed from the glass side of the samples and measurements of a Fe50Mn50/permalloy bilayer confirm that the sense of a hysteresis loop can change for a buried layer due to optical effects. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.369301
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