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The temperature dependence of the magnetization for Fe88Zr7B4Cu1 amorphous alloy has been measured. M(T) has been fit using a Handrich–Kobe model with a modified Brillouin function with an additional exchange fluctuation term. Here for the first time, an asymmetrical distribution of the exchange interactions is proposed based on empirical knowledge of the Bethe–Slater curve. A two-parameter exchange fluctuation is shown to give significantly better fits to M(T) for these amorphous alloys.

The equimolar alloy FeCoCrNi, a high-entropy alloy, forms in the face-centered-cubic crystal structure and has a ferromagnetic Curie temperature of 130 K. In this study, we explore the effects of Cr concentration, cold-rolling, and subsequent heat treatments on the magnetic properties of FeCoCrxNi alloys. Cr reductions result in an increase of the Curie temperature, and may be used to tune the TC over a very large temperature range. The magnetic entropy change for a change in applied field of 2T is ΔSm = −0.35 J/(kg K) for cold-rolled FeCoCrNi. Cold-rolling results in a broadening of ΔSm, where subsequent heat treatment at 1073 K sharpens the magnetic entropy curve. In all of the alloys, we find that upon heating (after cold-rolling) there is a re-entrant magnetic moment near 730 K. This feature is much less pronounced in the as-cast samples (without cold-rolling) and in the Cr-rich samples, and is no longer observed after annealing at 1073 K. Possible origins of this behavior are discussed.

In previously reported work FexCo1−x[C] (x=0.0, 0.2, 0.4, 0.5, 0.6, and 0.8 nominally) nanoparticles were prepared by a Kratschmer–Huffman carbon-arc method. Fe0.5Co0.5[C] exhibited the largest magnetizations heretofore observed in similarly produced nanoparticles. Here we present a more detailed study of the magnetic properties of Fe0.5Co0.5[C] nanocrystals. Magnetic hysteresis loops have been measured to temperatures exceeding 1050 K. This is attributed to rotational processes in monodomain particles and is shown to be sensitive to ordering of the particles. Low-field thermomagnetic data clearly show features which we attribute to the α→α′ disorder–order and α→γ phase transformations, respectively.

The Krätschmer–Huffman carbon-arc method of preparing fullerenes has been used to generate carbon-coated transition metal (TM) and TM-carbide nanocrystallites. The magnetic nanocrystallites were extracted from the soot with a magnetic gradient field technique. For TM=Co the majority of nanocrystals exist as nominally spherical particles, 0.5–5 nm in radius. Hysteretic and temperature-dependent magnetic response, in randomly and magnetically aligned powder samples frozen in epoxy, correspond to fine particle magnetism associated with monodomain TM particles. The magnetization exhibits a unique functional dependence on H/T, and hysteresis below a blocking temperature TB. Below TB, the temperature dependence of the coercivity can be expressed as Hc=Hc0[1−(T/TB)1/2], where Hc0 is the 0 K coercivity.