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  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Accurate measurements of the electrical resistivity (ρ,dρ/dT) and of the thermoelectric power (S,dS/dT) were performed in the ternary compounds U2Ni2In and Nd2Ni2Sn from 4 K to 250 K, and the results are compared with those previously obtained in U2Ni2Sn. The pair U2Ni2In/U2Ni2Sn enables us to study the influence of the p-electron character (and other band effects related to the elements In/Sn) on the transport properties, whereas the pair Nd2Ni2Sn/U2Ni2Sn provides direct information on the role played by the 4f/5f electrons. All these compounds order initially in the antiferromagnetic state, exhibiting a characteristic minimum in dρ/dT at TN. In the U2Ni2In compound a drastic reduction is observed in ρ(T) slightly below TN, suggesting the coexistence of the antiferromagnetic state with a coherent Kondo effect when T≤0.8 TN. In Nd2Ni2Sn we observe two distinct phase transitions below TN, of first-order character and likely associated with order-order magnetic transitions. The anomalous behavior of ρ(T) in the paramagnetic phase of the Nd2Ni2Sn compound can be satisfactorily described in terms of crystal field effects associated with the 4f-electron levels. © 1996 American Institute of Physics.
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetization, magnetic susceptibility, electrical resistivity, and specific heat measurements of UNiAl point to antiferromagnetic ordering below 19.3 K, which is confirmed by neutron-diffraction experiments. The enhanced γ value of 167 mJ/mol K2 is reflecting pronounced presence of magnetic fluctuations, which influence also the other electronic properties down to low temperatures. The thermal expansion of UNiAl was measured in the temperature range 1.5–210 K on a single crystal along the a and c axis. Similar to other bulk properties, also the thermal expansion of UNiAl is highly anisotropic. The a axis is monotonously expanding with increasing temperature in the whole temperature range. Along the c axis, the lattice first collapses with increasing temperature up to 35 K. Around this temperature, the thermal expansion coefficient αc changes sign and continuous expansion with further increasing temperature is then observed. The sharp anomaly of α near 19.3 K present in both directions is consistent with the magnetic phase transition. The results are discussed in terms of the presence of anisotropic magnetic fluctuations. © 1996 American Institute of Physics.
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: U2Pt2Sn is crystallizing in an ordered version (space group P42/mnm) of the tetragonal U3Si2 type of structure. Clear anomalies in the magnetic susceptibility, specific heat, and electrical resistivity around 15 K indicate that U2Pt2Sn orders antiferromagnetically below this temperature. As expected for an antiferromagnet, the susceptibility and specific heat anomalies are shifted to lower temperatures upon application of external magnetic field. The specific-heat coefficient γ=327 mJ/mol f.u. K2 remains unchanged in fields up to 5 T. The antiferromagnetic ground state of U2Pt2Sn can be concluded also from the metamagnetic transition around 22 T in the magnetization at 4.2 K and from magnetic reflections in the neutron-diffraction pattern at low temperatures. © 1996 American Institute of Physics.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed a detailed study of the magnetization of Y0.6U0.4Pd3 (Tf∼10 K), which shows thermal, transport, and magnetic properties typical of a spin-glass system. Strong irreversibility is observed among our zero-field-cooled and field-cooled measurements in fields as large as 30 kOe. Thus, the freezing temperature displays an unusual weak dependence with field. We observe a very slow temporal dependence of the magnetization below the freezing temperature. The nonlinear susceptibility coefficients extracted from our data show an increase by a factor of approximately 20 when approaching the freezing temperature from above, but do not show a true divergence at Tf, and a scaling analysis does not seem to be possible. We compare these results with those expected for classical spin glasses, and propose a possible mechanism for the onset of frustration below x=0.45 in Y1−xUxPd3. © 1996 American Institute of Physics.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The compounds CeRhSb and CeNiSn show hybridization gap in the electronic density of states. It is of interest to look for a similar gap in a related compound, CeNiSb. We present here the results of the structural, magnetic, and transport studies on CeNiSb. Rietveld analysis of the room-temperature neutron diffraction data reveals that this compound crystallizes in the hexagonal structure (space group P63/mmc). Magnetization measurements show that this compound is ferromagnetically ordered with a transition temperature of ∼4 K. The magnetic susceptibility of CeNiSb follows Curie–Weiss behavior between 10 and 300 K with effective paramagnetic moment close to that of Ce3+ ion. The heat capacity of CeNiSb shows a rise at about 4 K due to the ferromagnetic ordering and a moderately large value of γ is obtained. Its electrical resistivity shows a weak shallow minima at 15 K which is a characteristic feature of Kondo lattice systems. However, no rise in the resistivity at low temperatures, as seen in CeRhSb and CeNiSn, is observed in CeNiSb. © 1996 American Institute of Physics.
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  • 6
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The giant magnetoresistance (GMR) of magnetic multilayers is usually considered as isotropic, i.e., independent of the direction of the sensing current with respect to the applied field. In spin-valve samples of the form NiFe/Cu/NiFe/FeMn it is possible to accurately determine the amplitude of the GMR (without any contribution from the usual anisotropic magnetoresistance) for various direction of the current with respect to the direction of the magnetization of the two ferromagnetic layers, both in the parallel and antiparallel magnetic configurations. In three series of spin-valve samples of the composition F tF/Cu tCu/NiFe/FeMn, we have observed that the GMR amplitude is larger when the current is perpendicular to the magnetizations than when it is parallel to it. This intrinsic anisotropy in the GMR shows a pronounced maximum (relative amplitude of the anisotropy of the order of 10% at the maximum) for a thickness of the ferromagnetic layer of the order of 150 A(ring). In contrast, this anisotropy depends very weakly on the nonmagnetic spacer layer thickness. The results are compared with semiclassical calculations of Rijks et al. [Phys. Rev. B 51, 283 (1995)]. On another respect, we have measured the in-plane (CIP) and perpendicular to the plane (CPP) giant magnetoresistance of antiferromagnetically coupled (NiFe/Ag) multilayers. Particular attention has been paid on the variation of resistivity with the angle Δθ between the magnetization in the successive magnetic layers. While the CIP GMR varies almost linearly with cos(Δθ), the CPP GMR shows strong deviations from linearity especially at large NiFe thicknesses. The results are discussed in terms of relative role of s-like and d-like electrons in CIP and CPP transport. © 1996 American Institute of Physics.
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  • 7
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature dependence of the giant magnetoresistance (GMR) for currents parallel and perpendicular to the multilayer plane is discussed by taking account of the random exchange potentials, phonon scatterings, and spin fluctuations. The effect of spin fluctuations, which plays an important role at finite temperatures, is included by means of the static functional-integral method developed previously by the present author. Our model calculations well explain the observed features of the parallel and perpendicular GMR of Fe/Cr and Co/Cu multilayers recently reported by Gijs et al. [Phys. Rev. Lett. 70, 3343 (1993); Phys. Rev. B 50, 16 733 (1994)]. © 1996 American Institute of Physics.
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  • 8
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlocal real-space Kubo approach to electron transport in magnetic multilayers is applied to a new geometry, "oblique transport,'' whose complexity is traced back to a combination of the layering, of the nonlocal character of the linear response, and of the oblique direction transport in this new geometry. The problem is dealt with by applying a condition on the average current density vector or on the average electric-field vector, depending upon the external driving conditions. Its solution exhibits a characteristic anisotropy and it yields the global oblique conductance and magnetoresistance as simple trigonometric expressions in terms of the in-plane and vertical conductances and magnetoresistances, for arbitrary noncollinear-magnetization configurations. © 1996 American Institute of Physics.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new class of corrugated multilayers has been grown on silicon substrates which have (111) faceted grooves etched on their surface. These structures can be probed by conventional means with current at an angle to the plane of layers (CAP) as well as CIP. This angle is fixed by: the depth to width ratio of the grooves (which determines the angle θ), and the angle φ of the current probes with respect to the grooves. We have prepared multilayers of [Co(12 A(ring)) Cu(t)NiFe(12 A(ring)) Cu(t)]y with t=58 and 116 A(ring), and y=167 and 91 repeats, respectively; and have varied φ from 0 and 90° while θ is held fixed at 54.7°. We find the data is very well fit to the theoretical expression for CAP resistivity in terms of the more conventional CIP and CPP resistivities. From measurements of the CIP and CAP–MR's on these corrugated multilayers we are able to predict the CPP–MR for these structures. © 1996 American Institute of Physics.
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  • 10
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effects of magnetostatic interactions on the giant magnetoresistive (GMR) response of NiFe/Cu/NiFe spin valves are studied using an analytical model. The model is applicable to devices small enough for the magnetic layers to exhibit single-domain behavior. Devices having lengths in the track-width direction of 10 μm and interlayer separations of 4.5 nm are studied. Stripe heights are varied from 0.5 to 2 μm. The magnetization of one magnetic layer is pinned by a transverse pinning field that is varied from 0 to 24 kA/m (300 Oe). GMR curves for transverse fields are calculated. At zero external field the magnetization of the layers shows a tendency to align themselves antiparallel in the transverse direction. This results in an offset from the ideal biasing of the device. Broadening of the curves due to shape anisotropy occurs with decreasing stripe height and increasing magnetic layer thickness, and the magnetization in the pinned layer becomes less stable. © 1996 American Institute of Physics.
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