Structure And Magnetic Properties Of Co And Co-Fe,Co-Cu Nanowire Arrays

In areas of so many studies on nanomaterials, the nanowire has been paid much attention and widely studied. Especially the researches of magnetic nanowires have made large process. On the aspect of application, the magnetic nanowires could be made small magnetic devices;Due to the characteristic of one dimension, the magnetic nanowires could have large values of both the coercivity (H_c) and squareness ratio (S_q). It will be a much promising magnetic material for perpendicular magnetic recording with large density which can reach 100Gb/in~2.This paper is mainly focused on the crystal textures and magnetism of cobalt nanowire arrays as well as the magnetism of the cobalt alloy including Co-Fe and Co-Cu nanowire arrays. All the samples are prepared with the method of electrochemical deposition into anodic alumina oxide templates. Main points are as follows:1. The research attempted to change depositing voltage to observe its effects on the crystal texture of cobalt nanowire arrays with diameters of 20 run. The results of X-ray diffraction show a Hcp structure with strong (100) texture. By raising the depositing voltage another (110)texture was induced.2. The research attempted to change the pH value of depositing solution to observe its effects on the cobalt nanowire arrays. The results of X-ray diffraction show that the cobalt nanowire arrays with diameters of 20 nm form (100) texture , a mixture of (100) and (002) textures for 50 nm, and the (002) texture for 120 nm in the case of all pH values at 4.5. At a pH value of 6.7, the texture for 20 nm changed to (101) and (100) textures, a (002) texture for 50 nm, and a mixture of (100) and (101) textures for 120 nm. The magnetism of cobalt nanowire arrays also changes obviously for different textures. Especially for 50 nm, the H_c and S_g along the wire axes of nanowire arrays have a great increase because of the appearance of (002) texture.3. The research attempted to change the temperature of depositing solution to observe its effects on cobalt nanowire arrays. It is found that the temperature has no influence on the samples for 20 nm, but has a great effect on samples for 50 nm and 120 nm. The samples for 50 and 120 nm prefer forming (100) texture. Though the textures of samples for 20 nm don't change, the Hc increases obviously with raising temperatures. Due to the disappearance of (002) texture of samples for 50 nm, the Hc and Sq along the wire axes decrease when the temperature rises. However, the magnetism for 120 nm almost doesn't change with the changes of textures.4. Co(OAc)2 was chosen as the solution to deposit cobalt-molecular nanowirearrays. We chose templates with pore diameters of 120 nm which were anodized at the voltage of 80 V to deposit cobalt-molecular nanowire arrays. The XRD results showed an amorphous structure of all the samples. The SQUID measurements shows a different result compared to crystal cobalt nanowire arrays. When the temperature decreases, Ms increases obviously which is different with the T3/2 law. The Hc increases gradually in first step, and then decreases abruptly after the temperature decreases below about 50 K. The Hc at 5 K is smaller than at room temperature.5. Coi.xFex nanowire arrays with diameters of 20 nm were successfully prepared. SQUID measurements for samples (x=3.2%,5.5%, 8%) showed abnormal relations of Hc and Sq to the temperature. For the Co96.8Fe3.2 sample, the Hc and Sq decrease with decreasing the temperature. For the Co94.5Fe5.5 sample, the Hc and Sq don't change with decreasing the temperature.6. Coi.xCux nanowire arrays with diameters of 20 nm were successfully prepared, in which the x are 4 and 6.5%. SQUID measurements also showed abnormal relations of Hc and Sq to the temperature. For two samples, the Sq decreases with decreasing temperature and the Hc doesn't change.