Abstract
The magnetic properties of single crystalline hcp Co nanowire (NW) assemblies with different packing densities are investigated. The compacted assemblies exhibit an unusual increase in coercivity (HC) from 5.5 kOe to 6.1 kOe with the increase of the packing density from 2.1 to 4.5 g/cm3. While Hc decreases with further increase in packing density. A similar trend in Hc value variation with density has also been noticed at different temperatures. The initial increase in HC values is ascribed to magnetostatic interaction between the nanowires, which became stronger with the increased packing density. However, above the density of 4.5 g/cm3, the Hc decreases due to the proximity effect as shown in the δM plot. The δM plot shows a negative peak at high field and it becomes prominent with the increased density. Moreover, it has been found that the variation of HC with the packing density is also related to diameter of Co NWs. A larger diameter of the nanowires gives a negative dependence of the Hc value with the density in the whole investigated region.
Highlights
The magnetocrystalline anisotropy field (HA) is considered to be the theoretical upper limit of the coercivity in a ferromagnetic material and HA value of hcp Co is 7.6 kOe.7. Both the theoretical and experimental investigations have shown that the coercivity exceeding 10 kOe can be achieved in aligned Co NW assemblies, which is mainly ascribed to cooperating magnetocrystalline anisotropy and shape anisotropy contributions
The high coercivity in Co NWs is a very strong evidence for the formation of the hcp Co phase, X-ray diffraction (XRD) measurement was performed to examine the phase of as-prepared Co NWs before and after the compaction
We have shown that the magnetic properties of Co NW assemblies are strongly dependent on the packing density and diameter of the NWs
Summary
Magnetic nanowires have attracted substantial interests in recent years because of their potential applications in the ultrahighdensity magnetic recording media and future permanent magnets. the magnetic properties, the coercivity of NWs, can be tailored by precise control of the geometry and morphology, especially the mean diameter and aspect ratio. A typical example is hcp-structured Co NWs, which exhibit a giant shape anisotropy. In general, the magnetocrystalline anisotropy field (HA) is considered to be the theoretical upper limit of the coercivity in a ferromagnetic material and HA value of hcp Co is 7.6 kOe. both the theoretical and experimental investigations have shown that the coercivity exceeding 10 kOe can be achieved in aligned Co NW assemblies, which is mainly ascribed to cooperating magnetocrystalline anisotropy and shape anisotropy contributions. The above mentioned studies are mainly focused on the low-density NW assemblies, in which the effective magnetostastic interactions among the NWs are negligible. The magnetocrystalline anisotropy field (HA) is considered to be the theoretical upper limit of the coercivity in a ferromagnetic material and HA value of hcp Co is 7.6 kOe.. The magnetocrystalline anisotropy field (HA) is considered to be the theoretical upper limit of the coercivity in a ferromagnetic material and HA value of hcp Co is 7.6 kOe.7 Both the theoretical and experimental investigations have shown that the coercivity exceeding 10 kOe can be achieved in aligned Co NW assemblies, which is mainly ascribed to cooperating magnetocrystalline anisotropy and shape anisotropy contributions.. Note that the magnetostastic interactions may have a strong influence on the macroscopic magnetic behavior of the NW assembly and on the coercivity, which has not been thoroughly investigated in experiments
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