Temperature-Dependent Magnetic Properties of SiO 2 -Coated Ni 75 Fe 25 Nanoparticles
- PDF / 65,791 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 12 Downloads / 179 Views
DD5.17.1
Temperature-Dependent Magnetic Properties of SiO2-Coated Ni75Fe25 Nanoparticles Mingzhong Wu1, Y.D. Zhang*, S. Hui, and Shihui Ge Inframat Corporation, 74 Batterson Park Road, Farmington, CT 06032, U.S.A. 1 Department of Physics and Institute of Materials Science, University of Connecticut, Storrs, CT 06269, U.S.A. ABSTRACT SiO2-coated Ni75Fe25 nanoparticles were prepared using a wet chemical method and their structure and magnetic properties were investigated using x-ray diffraction, high-resolution transmission electron microscopy, and a superconducting quantum interference device magnetometer. The SiO2 material was in an amorphous state. The Ni75Fe25 nanoparticles were in a simple cubic state and contained inner oxide (Ni-oxide and Fe-oxide) cores whose size decreased with increasing calcination temperature. The nanoparticles were basically in the ferromagnetic state. Their saturation magnetization increased with increasing calcination temperature, whereas their coercivity decreased with increasing calcination temperature. The nanoparticles exhibited strong temperature-dependent magnetic behaviors. The Bloch exponent fell from 1.5 for the bulk to smaller values and decreased with increasing oxide content, while the Bloch constant was much bigger than that for bulk and increased significantly with oxide content. The value of coercivity decreased with increasing temperature, and this decrease was more pronounced for the nanoparticles containing high oxide content. The exchange anisotropy arising from the exchange coupling across the Ni75Fe25 /oxide interfaces was examined and was used to interpret the observed temperature-dependent behaviors. INTRODUCTION Studies on insulator-coated ferromagnetic nanoparticles have been and continue to be an area of great interest. From a fundamental perspective, the coated nanoparticles are of interest as the coating prevents the nanoparticles from particle coarsening, surface oxidation, and agglomeration. From an application perspective, the coated nanoparticles have attractive potential application in high frequency soft magnetic materials and clinical drug delivery. In soft magnetic applications, the coating not only works as an insulate phase to achieve high electrical resistivity, but also behaves as a binder to ease the consolidation of the nanoparticles. In drug delivery applications, the coating protects the metal nanoparticles from leaching in an acidic environment. A considerable amount of research has been conducted on the preparation and magnetic properties of insulator-coated ferromagnetic nanoparticles in the recent years, but most of them focused on Fe and Co nanoparticles [1-6]. We have recently synthesized SiO2-coated Ni75Fe25 nanoparticles and examined their structural and magnetic properties. The detailed synthesis procedure and structural properties have been presented elsewhere [7]. Here we present the magnetic properties of SiO2-coated Ni75Fe25 nanoparticles, especially the temperature-dependent saturation magnetization, coercivity, and exchange ani
Data Loading...
