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A comparative study of the structure and magnetic properties of Ni nanoparticles (20–80 nm) prepared by the chemical reduction of NiCl2 solution of four different concentrations is reported. The concentration of the NiCl2 solution has a profound influence on the room temperature (300 K) magnetic state of the resulting Ni nanoparticles, even though all four samples show the same x-ray diffraction (XRD) pattern, i.e., have the same crystal structure (tetragonal, as proposed by us). It is found that samples obtained from lower concentration solutions (0.1 and 0.5M) show a linear response with magnetic field while those obtained from higher concentration ones (1 and 2M) have a ferromagnetic component at 300 K. This difference in magnetic behavior has been attributed to the possible presence of fcc (face centered cubic) Ni cores in the particles of higher molarity samples, which therefore leads to strong interparticle dipolar interactions in them. The strong interactions, together with the magnetocrystalline anisotropy of the cores, present a significant barrier to the relaxation of core moments in these samples, giving rise to their blocked state even above 300 K, as evident from the irreversibility in the field cooled (FC) and zero field cooled (ZFC) curves, which starts right from the measuring temperature of 390 K. Intriguing features in the form of a sharp peak at 20 K and a hump at 12 K are observed in the ZFC curve of all samples, signaling magnetic transitions at these temperatures. Appreciably high magnetization values are also seen in the M-H plots at 5 K. The presence of these low temperature features irrespective of sample molarity indicates that the low temperature magnetic states of the samples, in contrast to their room temperature states, are independent of the concentration of the NiCl2 solution. [ABSTRACT FROM AUTHOR]

We report the direct epitaxial growth of equiatomic ordered antiferromagnetic PtMn layers by molecular beam epitaxy. Such layers are used in giant magnetoresistance spin valve sensors as the antiferromagnetic pinning layer. Structural characterization and phase identification confirmed the spontaneous formation of the chemically ordered face-centered-tetragonal (L10) phase of PtMn with about 87.4% ordering. Based on the antiferromagnetic PtMn layer, we prepared exchange-biased PtMn/NiFe bilayers with various PtMn thicknesses. The exchange anisotropy field of the bilayer with NiFe grown on PtMn stabilizes at about 50 Oe beyond a PtMn thickness of 15 nm. Although the exchange anisotropy field is small compared to that of the polycrystalline system, the antiferromagnetic domain structure is stable over repetitive external magnetic field cycling and no training effect is observed. [ABSTRACT FROM AUTHOR]

Provides information on a study that determined scattering length density profile in amorphous, diamondlike, hydrocarbon films by specular reflectivity of neutrons and x-rays. Methodology of the study; Results and discussion on the study; Conclusion.

Epitaxial Fe/Co bilayers were grown on MgO (001) substrates by molecular beam epitaxy, characterized in situ by reflection high-energy electron diffraction and ex situ by x-ray diffraction (XRD), as well as high-resolution transmission electron microscopy (HRTEM). The hexagonal close packed (hcp) structure in two perpendicular domains was identified for the Co layer using XRD and HRTEM techniques. Co is found to grow in the (11-20) orientation with the c axis in plane, parallel either to Fe[110] or Fe[1-10] The magnetic properties as a function of Co thickness in Fe (10 nm)/Co (t) (t=5–20 nm) bilayers were investigated. The Fe/Co bilayers exhibit in plane magnetization with easy axes parallel to Fe[100] and Fe[010] axes. The magnetic behavior is consistent with the orientation relationship between the Fe and Co layers. [ABSTRACT FROM AUTHOR]

The combination of Mössbauer spectroscopy and magnetization measurements is demonstrated to be efficient in the determination of the phases responsible for the glassy magnetic dynamics of the highly disordered alloy Fe[sub 35]Al[sub 50]B[sub 15] produced by mechanical alloying. Its spin-glass behavior is apparent from the FC-ZFC magnetization irreversibility, the thermoremanent magnetization, and the slightly frequency-dependent peak in the temperature dependence of the ac susceptibility. Furthermore, the maximum at T[sub p] ≈ 22 K in the real component of the ac susceptibility is accompanied by a sudden onset of the imaginary component. The fit of the frequency dependence of T[sub p] to the critical slowing down law yielded a critical exponent z v = 8 ± 1. However, Mössbauer spectroscopy uncovered the existence of two different Fe environments, of which only the minor one freezes at low temperatures into a distribution of magnetic sextets. This result, combined with the superparamagnetic behavior detected at moderate fields, allowed us to ascribe the spin glass behavior to the presence of interacting, very fine, ferromagnetic clusters (estimated size ∼ 1 nm). The origin of this nanoscale compositional heterogeneity is argued to be related to regions of partially unalloyed Fe. The conclusions are contrasted with other mechanically alloyed systems with reported spin glass behavior or compositional inhomogeneity. [ABSTRACT FROM AUTHOR]