A microstructural and crystallographic investigation of the precipitation behaviour of a primary Al3Zr phase under a high magnetic field
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The effects of a high magnetic field on the precipitation behaviour of the primary Al 3 Zr phase are investigated. With and without the field, the primary Al 3 Zr crystals possess three morphologies – small tabular crystals in the deposit layer, long bars and dendritic crystals. The dendritic crystals are probably those surviving from the initial material. The tabular crystals in the deposit layer are those surviving from the heating stage, whereas the long bars are those formed during cooling. With the field, the tabular crystals in the deposit layer and the long bars tend to orient with the 〈110〉 direction parallel to the field direction, but the orientation of the dendritic crystals is less affected. The orientation of the crystals in the deposit layer arises from their magnetocrystalline anisotropy, but that of the long bars and dendritic crystals is disturbed by gravity and the formation of compound twins, respectively. Increased Zr content raises the precipitation amount of the primary Al 3 Zr crystals but weakens the alignment tendency of the tabular ones in the deposit layer. The weakness of the alignment arises from interaction between the crystals.Keywords:
Magnetocrystalline anisotropy
We investigate magnetic coercivity in double perovskite related oxides, based on first principles calculations of the magnetic properties and magnetocrystalline anisotropy. The Re-based materials studied have large magnetic moments on Re (nearly 1 μB in Sr2CrReO6) and relatively large magnetocrystalline anisotropy energies. This is unexpected considering the octahedral coordination. Based on this, we studied an intergrowth of double perovskite Sr2CrReO6-like and SrTiO3-like blocks. We obtain a very high predicted coercive field in excess of 90 T. This shows that it is possible to have large coercive fields arising from magnetocrystalline anisotropy associated with transition elements in nearly cubic local environments.
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Using single crystal spheres of less than 1·5 mm diameter changes of anisotropy field of the order of 0·1 Oe may be determined; hence the induced anisotropy constants F and G. If necessary the measurement may be made in the presence of the very large anisotropy fields associated with the ordinary, typically cubic, magnetocrystalline anisotropy. Changes of about 0·01 Oe may be detected and the apparatus is stable to this degree over periods of some hours.
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Induced magnetic anisotropy is important in numerous technical applications. An in-plane easy axis may be induced in an electrodeposited alloy film by deposition in an applied field. The origin of this anisotropy is thought to be preferential alignment of pairs of atoms of the same species, and the effect is generally small compared to magnetocrystalline anisotropy or surface anisotropy. Despite the phenomenon being well established, many open questions remain, including what happens to the induced anisotropy as the film thickness is reduced, or what the minimum applied field required to induce anisotropy is. We have studied the induced anisotropy in electrodeposited Fe-Co-Ni(Cu)/Cu multilayers, and find that induced anisotropy is still observed for layer thicknesses down to 2nm. We have also shown that the field required to induce anisotropy in this system is extremely low. Furthermore, it is possible to engineer the anisotropy of the film as a whole by changing the direction of the applied field during growth.
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The Sm-Co permanent magnets have received intensive interests in the electromechanical and micro-electromechanical industry due to the high energy product and the high Curie temperature. The magnetocrystalline anisotropy affects the coercivity thus influences the energy product. Hence the magnetocrystalline anisotropy constant is an important parameter in practical utility. The anisotropy field (Ha) was determined by measuring the easy and hard axis magnetization on powder aligned in a field and fixed in epoxy. But it is difficult to get the powder of single domain and the metastable materials decompose during the powdering process. As a result, simulation is a good method to obtain the magnetocrystalline anisotropy constant. SmCo5, SmCo7, SmCo6.7Zr0.3 and SmCo6.7V0.3 are discussed in this study. TEM and X-ray diffraction are used to analysis the microstructure. First-principles density functional calculation is used for discussing the influence of atomic environment on microstructure, magnetization, and magnetocrystalline anisotropy. The total energy calculations show the third element doping (Zr or V) can stabilize the TbCu7 structure. The Zr or V atoms replace the 2e Co atoms. The calculated magnetic moment agreed with experiments within 6% difference. The calculated magnetocrystalline anisotropy constants are about 3~4 times smaller than the measured value. The trends are anisotropy (SmCo5) > anisotropy (SmCo7), anisotropy (SmCo6.7Zr0.3) > anisotropy (SmCo7), anisotropy (SmCo6.7V0.3) > anisotropy (SmCo7) which can be explained by the symmetry of atoms.
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A simplified form of the theoretical single‐ion, crystal field contribution to the magnetocrystalline anisotropy of RE2TM17 compounds is given. Through an evaluation of this contribution in Sm2(Co1−xFex)17 compounds, two methods of favourably altering their anisotropy were suggested. The first involves substitution of Sm by Tb in order to compensate the adverse influence of Fe beyond x?0.2. The expected effect is observed. Substitution of Co by Mn or Cr was used in an attempt to avoid the consequences of structural features of the Fe‐containing alloys upon the anisotropy. These new compounds yield up to 40% improvement in the anisotropy, and at high magnetizations, compared to Sm2Co17.
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Abstract The magnetocrystalline anisotropy of Co x Ni 1− x Fe 2 O 4 ± γ is measured at room temperature by torque measurements. It is found that an additional couple caused by the anisodropy of the magnetization must be taken into account in the determination of the magnetocrystalline constants. For the (100)‐plane is found that the magnetocrystalline anisotropy increases nearly linearly with the Co‐content. The constants k 1 of the anisotropy of the magnetization also increase linearly at low Co‐additions, but at higher Co‐concentrations the increase is less than linear. Measurements in the (111)‐plane show a marked dependence of L max on the magnetic field strength. Attempts to find the values of the constants by extrapolation prove unsuccesful.
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The temperature dependence of magnetocrystalline anisotropy constants and the saturation magnetization in a single variant state have been investigated for L10-type Fe60Pt40 bulk single crystal prepared under compressive stress. The uniaxial magnetocrystalline anisotropy constant Ku evaluated from the magnetization curve is 6.9×107ergcm−3 at 5K. The values of the second- and fourth-order magnetocrystalline anisotropy constants K1 and K2 at 5K determined by the Sucksmith–Thompson method are 7.4 and 0.13×107ergcm−3, respectively. Both the values of Ku and K1 decrease with increasing temperature T, while K2 is almost independent of T. The difference between the power law of the Callen and Callen model is described by the dimensionality and the thermal variation of the axial ratio c∕a due to the thermal expansion.
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The magnetic anisotropy of pure and Co/Ti-doped Ba ferrite particles is analyzed through the evaluation of the dependence on temperature of the constants of magnetocrystalline and shape anisotropy, which both are present in the platelet-like Ba ferrite particles with hexagonal structure. In undoped Ba ferrite, the magnetocrystalline anisotropy constant is predominant on the conflicting shape anisotropy constant at all temperatures, which indicates that the magnetic anisotropy is uniaxial, with preferred direction for the magnetization along the c axis of the hexagonal particles. In doped particles, where the magnetocrystalline anisotropy is weakened by the ionic substitutions, while at high temperatures the magnetic anisotropy is substantially uniaxial with c as axis of easy magnetization, when the temperature decreases, the shape anisotropy constant becomes larger than the magnetocrystalline anisotropy constant, and consequently, the magnetic anisotropy is not uniaxial, but it presents multiple preferred directions for the magnetization
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