Tunable Magnetic Properties in Metal Ceramic Composite Thin Films
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TUNABLE MAGNETIC PROPERTIES IN METAL CERAMIC COMPOSITE THIN FILMS D. Kumar*, J. Narayan**, A.K. Sharma**, A. Kvit**, C. Jin**, and J. Sankar *Center for Advanced Materials and Smart Structures, Department of Mechanical Engineering, North Carolina A & T State University, Greensboro, NC 27411. **Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695. ABSTRACT We have developed a novel thin film processing method based upon pulsed laser deposition to process nanocrystalline magnetic materials with accurate size and interface control. Using this method, single domain nanocrystalline Fe and Ni particles in 5-10 nm size range embedded in amorphous as well as crystalline alumina have been produced. Magnetization measurements of these layered thin films as function of field and temperature were carried out using a superconducting quantum interference device magnetometer. Hysteresis below blocking temperature have been found to be consistent with the Stoner-Wohlfarth type behavior. The size of Fe and Ni nanodots measured using transmission electron microscopy and calculated using magnetic data are in excellent agreement with each other.
INTRODUCTION Nanoscale magnetism currently provides a wealth of scientific interest and of potential applications.1-12 When the size of magnetic particles is reduced to a few tens of nanometers, they exhibit a number of outstanding physical properties such as giant magnetoresistance, superparamagentism, large coercivties, high Curie temperature, and low saturation magnetization as compared to the corresponding bulk values. For many magnetic applications, especially for high-density recording, the amplitude and the width are proportional to √MrHc and 1/Hc, respectively, where Hc is the coercivity and Mr is the remnant magnetization. Thus, larger Hc and Mr result in better recording
The coercivity characteristics.9-26 exhibits a strong dependence on the size of magnetic materials.10, 11, 25 Typically, the coercivity is zero up to a critical size and then it goes through a maximum. Absence of coercivity and remanence is associated with superparamagnetic behavior. Up to the coercivity maximum, nanocrystals behave as single domains and above this size there is a multi-domain behavior where coercivity decreases as the size increases. Therefore, the synthesis of magnetic systems with characteristic nanoscale dimension has attracted a lot of research attention. Inert gas condensation, sputtering, mechanical attrition, aerosol, ball milling, etc. are some of the common methods adopted to synthesize
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ultafine magnetic particles.4-6, 12-17 While most of these methods have met with considerable success, producing heterogeneous magnetic materials in a controlled compositional, structural and reproducible manner is still not satisfactory. It is in this context that we have developed a laser-assisted method to uniquely produce nanocrystalline materials in an amorphous insulating matrix. The method is generic in nature and can be applied to the synthes
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