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  • 1
    Digitale Medien
    Digitale Medien
    On the role of Zn in Sm2Fe17Nx permanent magnets : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6044-6046 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Coercivities up to 1.9 T were achieved by bonding micron-size Sm2Fe17Nx particles with zinc. X-ray analysis of Zn-bonded samples indicates the presence of the ZnFe Γ phase and no unreacted Zn, after heat treatment at about 390 °C for 100 min for samples with Zn content varying from 5 to 35 wt. %. The increase of coercivity occurs only for a more intense heat treatment, e.g., at 390 °C for 300 min or 425 °C for 100 min. Differential scanning calorimetry (DSC) shows two exothermic peaks at 388 and 426 °C, but no endothermic peak related to the melting of Zn (at 419.6 °C) was observed. In dilatometric measurements two peaks were observed for the rate of length change near the same temperatures as the DSC peaks. Polarization-versus-field curves point to an additional ferromagnetic phase with (i) a Curie temperature near 180 K and (ii) 2% of the net magnetization at low temperatures. The corresponding dip in low-temperature demagnetization curves, however, is about 10% in depth. Most of the Sm2Fe17Nx grains in the demagnetized Zn-bonded magnets are multidomain. We found γ≈3.4×10−2 J/m2 and Dc≈0.3 μm for the wall energy and for the critical single-domain particle diameter, respectively.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353464
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  • 2
    Digitale Medien
    Digitale Medien
    Magnetic reversal in Sm2Fe17Ny permanent magnets : 37th Annual conference on magnetism and magnetic materials (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 6047-6049 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Coercivity and nucleation fields for three-dimensional inhomogenities are calculated and discussed. For soft spherical inclusions in a hard magnetic matrix a (δ/R)2 dependence of the nucleation field on inclusion radius R and domain wall width δ has been obtained. To calculate propagation fields for spherical inhomogenities, a nonlinear model has been used. The corresponding coercive field can be much higher than the nucleation field, particularly if the magnitude of the anisotropy changes very steeply. Soft inclusions with sharp interfaces are ineffective at producing complete magnetic reversal. For partly nitrided particles coercivity and nucleation field are predicted to be identical, which is confirmed by experiments on high-performance Sm2Fe17N3−δ magnets.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.353465
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  • 3
    Digitale Medien
    Digitale Medien
    Sample size dependence of the critical current density in polycrystalline YBa2Cu3O7−δ (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2964-2968 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The zero-field transport critical current density 〈Jc〉 of polycrystalline YBa2Cu3O7−δ has been measured at 77 K for slabs of different thickness d. It was found that 〈Jc〉 increases as the thickness decreases. The experimental data is in agreement with a field-dependent Jc(H) that decreases with increasing field. However, a clear distinction between a Kim, exponential, and power law model cannot be made.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.351501
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  • 4
    Digitale Medien
    Digitale Medien
    First order magnetization processes in Nd(Fe, M)12Cy compounds (M=V, Ti, Mo) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5278-5280 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetization measurements on Nd(Fe, M)12Cy (M=Ti, V, Mo) with ThMn12-type structure have revealed well developed first order magnetization processes (FOMPs) when an external field is applied perpendicular to the c axis. The FOMPs depend on carbon concentration, temperature, and the type of M element. The FOMPs appear at a certain carbon concentration and at temperatures below 150–100 K. The FOMP fields of NdFe12−xVxCy are independent of the V content in the range x=1.25–2.0, which is due to the small change of the anisotropy field within this range. No FOMP has been found in the nitrides of the same parent alloys. The evaluation of the crystal field (CF) parameters shows that the higher-order CF parameters of the Nd ions play a key role in producing the observed type-II FOMP. The temperature dependence of the FOMPs is due to the thermal evolution of the anisotropy constants Ki (i=1,2,3) of the carbides. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.373320
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  • 5
    Digitale Medien
    Digitale Medien
    Magnetization processes in two different types of anisotropic, fully dense NdFeB hydrogenation, disproportionation, desorption, and recombination magnets (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6119-6121 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Two types of textured, fully dense NdFeB hydrogenation, disproportionation, desorption, and recombination (HDDR) magnets were produced. The first type was produced by hot pressing isotropic HDDR powder followed by die upsetting; the second, by hot pressing prealigned, anisotropic HDDR powder (MQA-T). Studies of the magnetization processes revealed that for isotropic HDDR powder and its hot pressed and die-upset magnets a much larger initial susceptibility is found after thermal demagnetization than after reverse dc-field demagnetization. Prealigned, hot pressed magnets made from MQA-T material showed a different virgin magnetization curve, indicating a unique coercivity mechanism. Interaction domains larger than the average grain size can be observed in both cases by Kerr microscopy, with the MQA-T type showing significantly broader interaction domains. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372628
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  • 6
    Digitale Medien
    Digitale Medien
    Highly coercive SmCo5 magnets prepared by a modified hydrogenation-disproportionation-desorption-recombination process (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5666-5668 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The hydrogenation-disproportionation-desorption-recombination (HDDR) process was applied to SmCo5 using extreme conditions, namely high hydrogen pressures and reactive milling under hydrogen. Investigations on the hydrogen absorption behavior of SmCo5 by differential scanning calorimetry under hydrogen pressures between 1 and 7 MPa showed absorption events due to an interstitial absorption at about 100 °C and a disproportionation reaction at about 600 °C. X-ray diffraction showed the disproportionation of SmCo5 into Sm hydride and fcc-Co. A favorable effect of high hydrogen pressures on the disproportionation reaction was observed which can be explained by a decrease of the free enthalpy of the samarium hydride for increasing hydrogen pressures. Reactively milled SmCo5 showed also the products of the disproportionation reaction. The recombination to the original SmCo5 phase on hydrogen desorption in a subsequent heat treatment in vacuum was successful for both methods. However, Sm2O3, Sm2Co17, and Sm2Co7 were detected as minor phases. Maximum coercivities μ0JHC of 2.1 and 4.7 T were achieved for high pressure and reactively milled HDDR powders, respectively. The high coercivities originate from the high anisotropy field of the SmCo5 phase in combination with the grain refinement due to the HDDR treatment. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.369834
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  • 7
    Digitale Medien
    Digitale Medien
    Magnetoresistance of polycrystalline layered manganites La2−2xSr1+2xMn2O7 (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 85 (1999), S. 5420-5422 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Polycrystalline bulk samples of the layered manganites La2−2xSr1+2xMn2O7 showing a colossal magnetoresistance (CMR) effect were prepared for doping levels of x=0.4 and 0.5 by a solid-state reaction route. Temperature and field dependences of magnetization and of electrical resistivity have been measured between 5 K and room temperature. Ferromagnetic behavior with a Curie temperature of TC=135 K and a high value of spontaneous magnetization (64 emu g−1) was found for x=0.4. The x=0.5 compound orders antiferromagnetically near TN=215 K, showing a resistivity enhancement there. The resistivity of the x=0.4 compound shows a field dependence at low temperatures similar to that found for polycrystalline La0.7Sr0.3MnO3. The resemblance includes the presence of both a low-field and a high-field contribution to the magnetoresistance, as well as the magnitude of the low-field MR (−23% at 20 K and −15% at 77 K for H=1 kOe). The low-field MR is attributed to the effect of grain boundaries. In contrast to the grain-boundary MR of La0.7Sr0.3MnO3, it was also observed at temperatures far above the TC of the layered manganite. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.369962
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  • 8
    Digitale Medien
    Digitale Medien
    Magnetotransport of La0.7Sr0.3MnO3/SrTiO3 multilayers with ultrathin manganite layers (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 89 (2001), S. 6973-6975 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The thickness dependence of electrical transport and magnetization of ultrathin La0.7Sr0.3MnO3 films has been investigated using epitaxial La0.7Sr0.3MnO3(LSMO)/SrTiO3 multilayers prepared by pulsed laser deposition. Layer thicknesses range from 1.9 to 10 nm for both constituents. Microstructural characterization by x-ray diffraction and transmission electron microscopy has confirmed a well-defined superlattice structure, coherent growth, and fairly smooth interfaces of the samples. Magnetization measurements show a pronounced drop of the ferromagnetic Curie temperature below a LSMO thickness of d=3 nm, accompanied by a strong rise of the coercive field. The in-plane electrical transport changes from metallic (dρ/dT〉0) to insulating at d∼2.3 nm. Three different types of magnetoresistance (MR) have been observed for d〈3 nm. In the sequence of decreasing d, the first resembles the grain boundary MR of polycrystalline LSMO, the second is positive, and the third is associated with a magnetic field-induced insulator-to-metal transition. Magnetic and transport results are discussed in the framework of a mixed-phase state of ferromagnetic metallic and less magnetically ordered insulating clusters in the ultrathin LSMO films. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1362649
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  • 9
    Digitale Medien
    Digitale Medien
    Hard magnetic properties of melt-spun R(Fe,M)12 nitrides (R=Nd or Pr; M=Mo or V) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 988-992 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The hard magnetic properties of nitrided melt-spun R(Fe,M)12 (R=Pr and Nd, M=V and Mo) ribbons have been investigated. Hard magnetic powders were prepared by vacuum annealing of ground ribbons in the temperature range from 700 to 950 °C and subsequent nitrogenation. For NdFe10.5Mo1.5Nx and PrFe10.5Mo1.5Nx powders, coercivities as high as 10.4 and 4.5 kOe at room temperature, respectively, were achieved by carefully controlling the nitrogenation process. The coercivity strongly depends on the preparation route, i.e., annealing temperature as well as nitrogenation temperature and time. By the detailed investigation of the influence of these conditions, the optimum process parameters were determined. The coercivity mechanism of melt-spun NdFe10.5Mo1.5Nx powders shows characteristics of a randomly oriented single domain particle system. Poor coercivities have been obtained for Nd(Fe,V)12 and Pr(Fe,V)12. In these cases as well as for not optimally nitrogenated Nd(Fe,Mo)12, the low coercivity of the nitrided powders is related to (i) too large grain sizes, (ii) the presence of α-Fe additional to the ThMn12-type phase, or (iii) a nonhomogeneous nitrogenation of the powder. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.373766
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  • 10
    Digitale Medien
    Digitale Medien
    Influence of Fe and Co additions on magnetization and magnetoresistivity of MnAu2 melt-spun alloys (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 5789-5791 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Melt-spun MnAu2 ribbons modified by ternary magnetic additions (Fe and Co) show a large giant magnetoresistance (GMR) effect up to a magnetoresistance ratio MR={[R(H=7T)−R(0)/R(0)]} of the order of −10% at room temperature. Pure MnAu2 samples show a transition from positive magnetoresistance at low temperatures (e.g., MR=+23% at 10 K and μ0H=5 T) to a GMR behavior with values of about −8% at 295 K and 5 T. At 135 K the resistivity is nearly independent of the applied magnetic field. The strong increase of |MR| at room temperature is only found with applied fields larger than a threshold field, where a metamagnetic transition occurs. Alloying the compound with Co or Fe this threshold field can be reduced or suppressed. This effect is due to softening of the antiferromagnetic behavior of the (Mn; Co or Fe)Au2 samples. For an alloy with 5 at. % Fe as substitutes for Mn, no metamagnetic transition is observed in the temperature range between 10 and 300 K. For both 5 at. % Co or Fe additions a GMR behavior is observed in this temperature range with higher sensitivity at low fields, e.g., (Mn0.95Fe0.05)Au2 has values of MR=−12% and −1% in a field of 1 T at 10 and 295 K, respectively. At low temperatures, an anomalous increase of resistance at higher fields (above 1–2 T) is observed for these alloys. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.372523
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