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  • Articles: DFG German National Licenses  (52)
  • Electronic Resource  (52)
  • 1
    Electronic Resource
    Electronic Resource
    Two spin-freezing behavior in concentrated amorphous ferrite oxides : 35th annual conference on magnetism and magnetic materials San Diego, California (USA) 29 Oct − 1 Nov 1990 (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 5072-5074 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Amorphous CoFe2O4 with metal ions coordinated in a manner similar to the spinal crystal was prepared by the ion-beam sputter deposition method. The study of magnetic properties was carried out by dc- and ac-susceptibility measurements and Mössbauer spectroscopy. The strong spin-freezing behavior was observed in 80-Hz, 1-Oe ac susceptibility at two spin-freezing temperatures: 284 K (Tf1), which is considered to be caused by a random anisotropy of Co ions coordinated in distorted octahedral sites, and 86 K (Tf2), which might be caused by the frustration of antiferromagnetic interactions due to the amorphous structure. The dc susceptibility showed irreversibility below Tf1 which decreased with increasing applied field. However, a distinct change was not observed at Tf2. The Mössbauer spectrum revealed that some of the paramagnetic Fe ions were frozen below Tf1, with relaxation phenomena, and that the residual paramagnetic ions were frozen at Tf2. The time decay of the thermoremanent magnetization observed below Tf1 showed different behavior compared to that above and below Tf2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.348126
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  • 2
    Electronic Resource
    Electronic Resource
    Magnetic and magnetoresistance properties in Ni80Fe20/Cu multilayers with in-plane uniaxial magnetic anisotropy (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 4096-4101 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic properties and magnetoresistance were investigated for Ni80Fe20/Cu multilayers with different Ni80Fe20 and Cu thicknesses that were prepared on an MgO (110) substrate using ion beam sputtering with different Ar ion acceleration voltage (VB). The structure of Ni80Fe20 is epitaxial distorted face centered tetragonal with (110) orientation, as was determined by x-ray and electron diffraction measurements. Thus, the induced in-plane uniaxial magnetic anisotropy depends on the VB and the Ni80Fe20 layer thickness. A giant magnetoresistance at room temperature was obtained up to 20% for (15 A(ring) Ni80Fe20/10 A(ring) Cu)60 multilayers, and oscillated for Cu layer thickness with 12 A(ring) period. The saturation field Hs for the giant magnetoresistance (GMR) is in good agreement with 2J/dMs, where J, d, and Ms are layer exchange coupling, magnetic layer thickness, and saturation magnetization, respectively. The small field changes ΔH of 20 and 8 Oe needed for GMR were attained for n=16 (MR=12%) and 2 (MR=6.5%), respectively, in (70 A(ring) Ni80Fe20/10 A(ring) Cu)n with in-plane uniaxial anisotropy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354455
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of a large amount of Co substitution on the magnetic properties of NdFeCoGaB magnets (abstract) (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4777-4777 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have found that a NdFeCoGaB sintered magnet containing 30 at. % Co still shows high coercive force in spite of such a large amount of Co substitution. The Curie temperature of the magnet is higher than that of the ternary NdFeB magnet by 280 °C. As a result, the following magnetic properties have been attained for Nd14.5Fe46Co30Ga1B8.5: Tc=590 °C, Br =11.7 kG, Hci =14.3 kOe, and (BH)max=32 MG Oe. Furthermore, in this magnet there exists an additional phase, Nd1(FeCoGa)4B1 with Ce1Co4B1 structure, which, as far as authors know, has not been reported to exist in the NdFeB-based magnets. In this study we investigated the magnetic properties and microstructure of Nd14.5Fe76−xCoxGa1B8.5 (x=16–50) sintered magnets. The high coercive force can be obtained in the Co-content region from 16 to 30 at. %. In particular, the magnet with 30 at. % Co shows coercive force as high as 14.3 kOe. However, further substitution of Co drastically deteriorates the magnetic properties. The coercive force of the magnet with 50 at. % Co is less than 1 kOe. From the metallographical point of view, the above-mentioned Nd1(FeCoGa)4B1 phase is not observed in the magnets containing less than 30 at. % Co. This phase abruptly appears in the magnet with 30 at. % Co and its amount increases with increasing Co content. The strongest x-ray-diffraction peak observed in the magnet with 50 at. % Co comes from the Nd1(FeCoGa)4B1 phase. The demagnetization-curve measurements suggest that reverse magnetic domains are nucleated in the Nd1(FeCoGa)4B1 phase at a low reverse magnetic field. It is noteworthy that the magnet with 30 at. % Co maintains the high coercive force in spite of the existence of such a soft magnetic phase. Details will be discussed in the coming session.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344784
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  • 4
    Electronic Resource
    Electronic Resource
    Double tunnel junctions for magnetic random access memory devices (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6064-6066 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Optimum junction resistance and minimum tunnel magnetoresistance (TMR) ratio required for high density and high performance magnetoresistive random access memory (MRAM) devices with a TMR cell plus field effect transistor (FET) switch architecture are discussed by taking into account the variation of FET resistance causing noise. This implies that a TMR ratio over 25% at a 400 mV bias voltage and junction resistance of several tens of kilo-ohms for TMR cells are required with a signal voltage of 30 mV and a sense current of 10 μA, which leads to about 10 ns read time. This large magnetoresistance ratio at the elevated bias voltage requires low bias voltage dependence of TMR for the MRAM devices. In order to try to meet this requirement, double tunnel junctions were fabricated which possess the central ferromagnetic layer consisting of a thin discontinuous layer of hard ferromagnetic Co80Pt20 nanoparticles and insulating Al2O3 prepared by alternate sputtering of Co80Pt20 and Al2O3 targets. The maximum TMR obtained was 20.5% at room temperature for FeCo top and bottom electrodes without annealing. Bias voltage dependence of the (NiFe/CoFe)/1.5 nm Al2O3/discontinuous CoPt/2.6 nm Al2O3/(CoFe/NiFe) double tunnel junctions were revealed to be small compared to that of single junctions, the barrier of which was also fabricated by sputtering of an Al2O3 target. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372613
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  • 5
    Electronic Resource
    Electronic Resource
    Reduction of saturation magnetic field in superlattices by addition of subsidiary ferromagnetic layers (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 1662-1666 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The saturation magnetic field along the hard axis, Hsh for the giant magnetoresistance is studied theoretically within the continuum approximation in a composite magnetic film consisting of a conventional magnetic sandwich film and subsidiary soft ferromagnetic layers epitaxially grown on both sides of it. The Hsh is given as a solution of an equation, which describes the interplay between dimensions and the magnetic properties of the subsidiary layers and the conventional magnetic sandwich film. By analyzing the effect due to the subsidiary layers, a drastic reduction of the Hsh is shown. Since the subsidiary layer is coupled ferromagnetically to the ferromagnetic layer of the sandwich structure, the rotation of the magnetization in a subsidiary layer in an external magnetic field can easily induce the rotation of the magnetization in an adjacent magnetic layer. The calculated results for the Hsh are in good agreement with the experimental results. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358854
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  • 6
    Electronic Resource
    Electronic Resource
    Correlation between giant magnetoresistance and the antiferromagnetic volume fraction in superlattices (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8598-8602 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We investigated the giant magnetoresistance (GMR) of metallic magnetic superlattices and its correlation to the volume fraction of antiferromagnetically aligned magnetic layers. It is assumed that the superlattices are composed of a mixture of regions having, respectively, antiferromagnetic and ferromagnetic alignments. The calculated correlation curves for Co/Cu and FeNiCo/Cu superlattices show good agreement with the experimental results. The upper limits of the GMR in these superlattices are predicted in the case of a perfect antiferromagnetic alignment. It is shown that the observed nonlinear behavior of correlations is attributed to the film quality of superlattices. By assuming the existence of different regions of ferromagnetic but antiparallel alignment, it is understood that the observed results of no GMR for small volume fraction are due to an apparent phenomenon. The GMR is analyzed from the point of view of the preparation conditions of superlattices. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362456
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of Ga addition to NdFeCoB on their magnetic properties (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 1043-1045 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It was found that the Ga addition to NdFeCoB magnets was very effective for improving their magnetic properties. Magnets with high boron concentration had a high coercive force and magnets with low boron concentration had a high-energy product. The following magnetic properties were obtained: (1) Nd14.5FebalCo16Ga1B9.5:Br=12.0 kG, IHc=15.3 kOe, (BH)max=34 MGOe, Tc=500 °C (2) Nd14.5FebalCo16Ga1B5.5:Br=13.1 kG, IHc=12.2 kOe, (BH)max=40 MGOe, Tc=500 °C. It was also found that NdFeCoGaB magnets with very low boron concentration still had a relatively high coercive force.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98773
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of large boron additions to magnetically hard Fe-Pt alloys (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2537-2540 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic properties were investigated for the ternary (Fe0.6Pt0.4)100−xBx and (Fe1−yPty)83B17 alloy ribbons prepared by the twin roll technique. Boron changes the compositions of the ordered FePt (γ1) phase, which coexists with Fe2B at various alloy compositions so that the actual Pt content of γ1 in the ternary alloy goes up with increasing boron content. Coercive force increase due to boron addition is remarkable, in particular at low Pt concentration. Annealing time to get high coercivity becomes much shorter by boron addition. iHc=5.6 kOe and 4πMs=7.8 kG were obtained in the (Fe0.65Pt0.35)83B17 ribbon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341638
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  • 9
    Electronic Resource
    Electronic Resource
    Very low loss ultrathin Co-based amorphous ribbon cores (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6050-6052 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ultrathin Co-based amorphous ribbons with a thickness of 6–10 μm were fabricated by a single roller quenching method in vacuum. The compositions of the alloys were zero magnetostrictive: Fe4.7Co70.3Si15B10 and (Fe0.05Co0.95)71(Si0.5B0.5)29. The ribbons obtained had good smoothness and dimensional uniformity. The core loss of toroidal samples 15 mm in diameter was measured after annealing. The loss decreased with decreasing ribbon thickness. In the case of 6.4-μm-thick (Fe,Co)71(Si,B)29 amorphous ribbon, the values at 100 kHz and 1 MHz were 40 mW/cm3 and 1.8 W/cm3 for Bm=0.1 T, respectively. The former was 1/4 that of Mn-Zn ferrites or 1/2 that of 5-μm-thick Supermalloy tape wound core loss. The latter was (2)/(3) that of 5-μm Supermalloy tape wound core loss. In addition, the initial permeability beyond 100 kHz was also markedly improved by thickness reduction. The values of 6.4-μm-thick (Fe,Co)71(Si,B)29 ribbon measured at 1 and 10 MHz were about 7000 and 1000 for Hm=2 mOe, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342151
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  • 10
    Electronic Resource
    Electronic Resource
    New application of complex magnetic materials to the magnetic refrigerant in an Ericsson magnetic refrigerator (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 3873-3878 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A complex new magnetic refrigerant, suitable for the ideal Ericsson cycle, has been investigated. Above ∼15 K it is necessary to use ferromagnets as a magnetic refrigerant. However, temperature variation for the magnetic entropy change in a homogeneous ferromagnet is not suitable for the Ericsson cycle. The present paper verifies, from theoretical analysis, that a complex ferromagnetic material, for instance, (ErAl2)0.312(HoAl2)0.198 (Ho0.5Dy0.5Al2)0.490, has the most suitable characteristics for the ideal Ericsson cycle, including two kinds of isomagnetic field processes. On the basis of the above consideration, a sintered layer structural complex has been prepared, composed of three kinds of RAl2.15 layers, where R's are rare-earth atoms. From specific heat measurements made on this complex, its entropy and entropy change have been determined. It has been concluded that the complex magnetic material is the most hopeful refrigerant for the Ericsson cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339232
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