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In 3 d − 4 f intermetallic compounds, a Co substitution for Fe usually strengthens the exchange interactions due to a shift of the Fermi energy to a region of the 3 d band with higher density of states. Here, we study the influence of Co on the magnetism of ferrimagnetic DyFe 5 Al 7 using magnetization measurements in static (up to 14 T) and pulsed (up to 58 T) magnetic fields. We find that the homogeneity range of DyFe 5− x Co x Al 7 is limited to x ≤ 2.5 . The Co substitution for Fe produces a strong detrimental effect on the 3 d − 3 d intrasublattice exchange interactions, which leads to a pronounced decrease of the Curie temperature and of the 3 d − 4 f intersublattice exchange field. A reduction of the density of states at the Fermi level might occur due to a broadening of the 3 d band. A decrease of the rare-earth contribution to the magnetic anisotropy energy is also observed with increasing Co content. This is attributed to a competition between the Fe and Co contributions to the crystal electric field at the Dy site. [ABSTRACT FROM AUTHOR]

The study of singularities in the magnetization curve of magnetic materials is since a long time a well known tool to gain insight into the material properties. Such singularities are usually due to discontinuous magnetization processes related to magnetic anisotropy, therefore an ideal investigation scheme would comprise magnetization measurements along the symmetry axis of a single crystal. As a matter of fact, one has to often deal with polycrystalline samples: in that case, however, the singularities can still be detected at the same positions as for the single crystal case. In this paper we focus on ferrimagnetic materials with uniaxial magnetic anisotropy. After recalling how theory allows us to calculate the critical fields at which singularities occur when the magnetic field is applied along a symmetry direction, we show that a new type of singular point not yet reported in the literature can exist. Such new singularity appears only in polycrystalline samples. We derive its analytical expression and we also show that, in spite of the need to overcome the exchange interaction, combinations of the material parameters can occur for which it falls inside experimentally accessible region. [ABSTRACT FROM AUTHOR]

Millimeter wave (MMW) absorption measurements have been conducted on commercial samples of large (micrometer-sized) and small (nanometer-sized) particles of BaFe12O19 and SrFe12O19 using a quasi-optical MMW spectrometer and a series of backwards wave oscillators encompassing the 30–120 GHz range. Effective anisotropy of the particles calculated from the resonant absorption frequency indicates lower overall anisotropy in the nano-particles. Due to their high magnetocrystalline anisotropy, both BaFe12O19 and SrFe12O19 are expected to have spin resonances in the 45–55 GHz range. Several of the sampled BaFe12O19 powders did not have MMW absorptions, so they were further investigated by DC magnetization and x-ray diffraction to assess magnetic behavior and structure. The samples with absent MMW absorption contained primarily iron oxides, suggesting that MMW absorption could be used for quality control in hexaferrite powder manufacture. [ABSTRACT FROM AUTHOR]

Tunability of structural and magnetic properties of Mn 3- x Co x Ga films is presented by Co substitution, where critical behavior emerges 0.37 ≤ x ≤ 0.56 exhibiting a transition from tetragonal hard ferrimagnetic with perpendicular magnetic anisotropy (PMA) to a cubic soft ferrimagnetic phase with in-plane magnetic anisotropy (IMA). In the critical regime, coexisting state of tetragonal and cubic phases possesses significantly low coercive field (H C = 1.9 kOe) with relatively low saturation magnetization (M S = 100~150 emu/cc) while maintaining the PMA. From first-principles calculations, moments of two Mn sites do not change upon Co substitution. However, moments of substituted Co almost vanish in tetragonal while giving around 1 μ B in cubic phase, which agrees with overall M S behaviors of the experimental results. These findings not only uncover the hidden magnetic state in Mn 3- x Co x Ga by altering the parallel and antiparallel coupling between Mn and Co, but also provide an additional degree of freedom for spintronic applications using Mn-based Heusler compounds. • Critical regime during the transition from hard ferrimagnetic tetragonal to soft ferrimagnetic cubic in Co-substituted Mn3Ga. • Dramatic reduction of the coercive field on remaining perpendicular magnetic anisotropy in the critical regime. • Compensation point near this critical regime due to a large reduction of the Co moments when substituted in Mn 3 Ga. [ABSTRACT FROM AUTHOR]