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Notes: A new low-field resonance technique for determining the initial hard-axis permeability (μ') of materials used in thin film and magnetoresistive heads has been developed. The initial μ' is found to be less than 4πM/Hk due to the internal effective magnetostatic field caused by magnetization ripple, in agreement with the theory and transverse biased initial susceptibility measurements of Hoffmann and others.1 A proper consideration of the in-plane susceptibility for real films includes the Stoner–Wohlfarth anisotropy field (Hk)−1 dependence, modified by the factors due to ripple (B) and skew (E) as defined by Hoffmann. The latter produce internal fields that shift the Kittel resonance versus field plots (fr2 vs H) leftward from their ideal symmetric positions for angles of 0° and 90° between bias field and preferred axis. When resonance data from both orientations are computer-fit simultaneously, we determine the parameters B and E as well as Hk and Ms. The coefficients are believed to have more consistency than those obtained using Hk found from hard-axis magnetization curves. The reduction of the hard-axis μ' is by the factor (1+B+E)−1. The high frequency properties (300 kHz–3 GHz) were measured using a test jig consisting of a shorted-shield strip-line section with a one-turn inductively coupled loop containing the sample and located at the shorted end. Bias fields from zero to 100 Oe were employed. We measure fR reproducibly with an uncertainty of less than 1%. This analysis determines the parameters of interest from measurements under dynamic conditions. Results include Permalloy and amorphous TM-metalloid films. When annealed to reduce Hk, their B parameters increase in accord with theory, assuming invariant structure constants, S. Beyond head applications, the method relates to thin film microwave devices operating near fr in zero field.2

Notes: The ternary alloy system Fe-Co-Al exhibits a little-noticed anomaly in that some alloys containing Al have higher Curie points than their undiluted counterparts. New results present the evolution of Curie point and saturation magnetization as a function of Al content, especially below 7 wt % (∼13.5 at. %) in the midrange of the Fe-Co composition field. Maxima of Tc in the range of 1000–1025 °C are found for Al contents of about 2–5 wt % (4–10 at. %) for alloy series with 30- , 40- , and 50-wt % Co (∼27- , 37- , and 47-at. % Co). These values are some 25–45 °C higher than the corresponding zero-Al alloys. Correlation of low-field thermal hysteresis and saturation-field thermomagnetic curves indicate first-order Curie point behavior at low-Al content, followed by classical second-order transitions at and above the Al content corresponding to Tc maxima. The former follow the α-bcc to the γ-fcc phase transition. For the latter class the α phase has been stabilized to higher temperatures with a relatively uncommon Curie point enhancement behavior.

Notes: Disordered suspensions of conducting particles exhibit substantial permittivity enhancements beyond the predictions of the Clausius–Mossotti equation and other purely dipolar approximations. The magnitude of the enhancement depends upon the shape of the particles. A recently developed effective cluster model for spherical particles [Phys. Rev. B 42, 9319 (1990)] that treats a disordered suspension as a mixture, or mesosuspension, of isolated spheres and close-packed spherical clusters of arbitrary size is in excellent agreement with experiments on well-stirred suspensions of spheres over the entire accessible range of volume loading. In this paper, the effective cluster model is extended to be applicable to disordered suspensions of arbitrarily shaped conducting particles. Two physical parameters are used to characterize a general suspension: the angular average polarizability of an isolated particle, and the volume loading at closest packing of the suspension. Multipole interactions within the clusters are treated exactly. External particle-shape-dependent interactions between clusters and isolated particles are treated in the dipole approximation in two ways: explicitly, using the Clausius–Mossotti equation, and implicitly, using the Wiener equation. Both versions of the model are used to find the permittivity of a monodisperse suspension of conducting spheroids, for which the model parameters can be determined independently. The two versions are in good agreement when the axial ratio of the particles is not extreme.The Clausius–Mossotti version of the model yields a mesoscopic analogue of the dielectric virial expansion. It is limited to small volume loadings when the particles have an extremely nonspherical shape. The Wiener equation version of the model holds at all volume loadings for particles of arbitrary shape. Comparison of the two versions of the model leads to a simple physical interpretation of Wiener's equation. The models are compared with experiments of Kelly, Stenoien, and Isbell [J. Appl. Phys. 24, 258 (1953)] on aluminum and zinc particles in paraffin, with Nasuhoglu's experiments on iron particles in oil [Commun. Fac. Sci. Univ. Ankara 4, 108 (1952)], and with new X-band and Kα-band permittivity measurements on Ni-Cr alloy particles in a polyurethane binder.

Notes: The ternary alloy family Fe–Co–Al is studied in the body-centered cubic (α) phase for the behavior of structure-insensitive magnetic parameters, out to compositions of 13 wt. % Al and 50 wt. % Co. Interest in this family on the potentially practical side derives from the properties of its separate iron binary systems. Iron–aluminum alloys have been investigated since before the turn of the century and there have been several efforts at commercialization as soft magnetic material. Iron–cobalt alloys have received special attention because of their high saturation magnetization (exceeding that the Fe), as well as for their very high Curie temperatures. However, the ternary system has received only sporadic attention, starting with the phase diagram and Curie point work of Köster one-half century ago and resumed largely for scientific interest in the electronic properties of transition metal alloys. Room-temperature magnetizations on a mass basis and on the more practical volume basis are presented. These expand upon earlier low temperature results. The presence of a broad maximum in magnetization in the Fe–Co binary does not persist beyond about 5 wt. % Al in the ternary family. Curie point results add to the data base and confirm those of Köster including an anomalous increase of Curie point with Al dilution for a certain range of composition. This feature is explained in terms of the bcc–fcc (α–γ) structure transition and the stabilization of the α-phase by Al additions.