Magnetization Characteristics of Oriented Single-Crystalline NiFe-Cu Nanocubes Precipitated in a Cu-Rich Matrix.

In this study, we evaluated the magnetization properties of a magnetic alloy with single-crystalline cubic nanostructures, in order to clarify its magnetocrystalline anisotropy. Upon applying a specific annealing treatment to the CuNiFe base material, the precipitated magnetic particles grew into cubic granules, resulting in the formation of nanometric cubic single crystals of magnetic CuNiFe in a nonmagnetic Cu-rich matrix. The cubic nanostructures of CuNiFe were oriented along their crystallographic axis, in the <100> direction of the face-centered-cubic structure. We evaluated the static magnetization properties of the sample, which originated primarily from the CuNiFe nanocubes precipitated in the Cu-rich matrix, under an applied DC magnetic field. The magnetocrystalline anisotropy was readily observed in the magnetization curves. The <111> axis of the CuNiFe was observed to be the easy axis of magnetization. We also investigated the dynamic magnetization properties of the sample under an AC magnetic field. By subtracting the magnetic signal induced by the eddy current from the magnetization curves of the sample, we could obtain the intrinsic AC magnetization properties of the CuNiFe nanocubes.

Study on the microstructures and the magnetic properties of precipitates in a Cu75-Fe5-Ni20 alloy.

The microstructural evolutions of precipitates formed in a Cu75-Fe5-Ni20 alloy on isothermal annealing at 873 K and 1073 K have been investigated by means of transmission electron microscopy (TEM). Nano-scale magnetic particles were formed randomly in the Cu-rich matrix after receiving a short annealing due to phase decomposition in the alloy. With increasing the isothermal annealing time, however, the striking features that two or more nano-scale particles with a cubic shape and a rod shape were aligned linearly along (100) directions were observed on isothermal annealing at 873 K and 1073 K, respectively. To investigate electro-magnetic properties of precipitates in a Cu-Fe-Ni alloy, the superconducting quantum interference device (SQUID) magnetometer and physical property measurement system (PPMS) were also complemented. The present study revealed significant influences that the magnetic properties of the specimens were closely related to the microstructures in the Cu-Fe-Ni alloy, which microstructures significantly depend on the isothermal annealing temperature.

Nano-scale precipitates formed in Cu-Co based alloys and their magnetic properties.

The microstructural evolutions of nano-scale magnetic Co particles formed in Cu-Co base alloys have been investigated on isothermal annealing at 973 K, using transmission electron microscopy (TEM). After the solution treatment and short annealing, nano-scale magnetic particles appeared randomly in the Cu-rich matrix. With increasing the isothermal annealing time, however, pairs and sometimes more than two of Co precipitates were linearly arranged along <100> directions in Cu-Co alloys. On the other hand, such linear arrangements of precipitates were extended in Cu-Ni-Co alloys. Co precipitates were cubic in the coherent stage and octahedral in incoherent stage of precipitation in binary alloys, while the precipitates rendered rectangular shapes even in the incoherent stage in Cu-Ni-Co. The magnetic properties of the specimens have also been measured at the similar conditions, with the superconducting quantum interference device (SQUID) magnetometer. The present study revealed that coersive forces of the specimens were correlated with the microstructural evolution occurring during the isothermal annealing.

TEM study and magnetic measurements of precipitates formed in Cu-Fe-Ni alloys.

The precipitation behavior of Cu-Fe alloys with Ni addition on isothermal annealing at 878 K was investigated by means of transmission electron microscopy (TEM), electron dispersive X-ray spectroscopy (EDS), and field-emission scanning electron microscopy (FE-SEM). Magnetic element atoms were segregated from the solid solution in supersaturated state, and nano-scale magnetic particles were randomly formed in the copper matrix at the initial stage of annealing at 873 K. With increasing the isothermal annealing time, however, the striking feature that two or more nano-scale magnetic particles with a cubic shape aligned linearly along (100) directions were observed upon the isothermal annealing at 873 K. To investigate the relationship between micro-structures and magnetic properties of the heterogeneous Cu-Fe-Ni alloys, magnetic measurements such as M-H measurements were also carried out, using a superconducting quantum interference device (SQUID) magnetometer. In this study, it was revealed that the magnetic properties of the specimen presented the ferromagnetic behavior, during the precipitation process in a Cu-Fe-Ni alloy.