High-Temperature First-Order-Reversal-Curve (FORC) Study of Magnetic Nanoparticle Based Nanocomposite Materials
- PDF / 666,414 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 79 Downloads / 133 Views
High-Temperature First-Order-Reversal-Curve (FORC) Study of Magnetic Nanoparticle Based Nanocomposite Materials B. Dodrill1, P. Ohodnicki2, M. McHenry3, A. Leary3 1
Lake Shore Cryotronics, Inc., 575 McCorkle Blvd., Westerville, OH, USA
2
National Energy Technology Lab, 626 Cochrans Mill Road, Pittsburgh, PA, USA
3
Carnegie Mellon University, Materials Science and Engineering, 5000 Forbes Ave., Pittsburgh, PA, USA ABSTRACT First-order-reversal-curves (FORCs) are an elegant, nondestructive tool for characterizing the magnetic properties of materials comprising fine (micron- or nano-scale) magnetic particles. FORC measurements and analysis have long been the standard protocol used by geophysicists and earth and planetary scientists investigating the magnetic properties of rocks, soils, and sediments. FORC can distinguish between single-domain, multi-domain, and pseudo single-domain behavior, and it can distinguish between different magnetic mineral species [1]. More recently, FORC has been applied to a wider array of magnetic material systems because it yields information regarding magnetic interactions and coercivity distributions that cannot be obtained from major hysteresis loop measurements alone. In this paper, we will discuss this technique and present high-temperature FORC results for two magnetic nanoparticle materials: CoFe nanoparticles dispersed in a SiO 2 matrix, and FeCo-based nanocrystalline amorphous/nanocomposites. INTRODUCTION The most common measurement that is performed to characterize a material’s magnetic properties is measurement of the major hysteresis loop M(H). The parameters that are most commonly extracted from the M(H) loop are: the saturation magnetization M s , the remanence M r , and the coercivity H c . First-order-reversal-curves (FORCs) [2] can give information that is not possible to obtain from the hysteresis loop alone. These curves include the distribution of switching and interaction fields, and identification of multiple phases in composite or hybrid materials containing more than one phase [3,4]. A FORC is measured by saturating a sample in a field H sat , decreasing the field to a reversal field H a , then measuring moment versus field H b as the field is swept back to H sat . This process is repeated for many values of H a , yielding a series of FORCs. The measured magnetization at each step as a function of H a and H b gives M(H a , H b ), which is then plotted as a function of H a and H b in field space. The FORC GLVWULEXWLRQȡ + a , H b ) is the mixed second derivative, LHȡ + a , H b ) = - 2 M(H a , H b + a + b . 7KH)25&GLDJUDPLVD'RU'FRQWRXUSORWRIȡ + a , H b ). It is common to change the coordinates from (H a , H b ) to H c = (H b - H a )/2 and H u = (H b + H a )/2. H u represents the distribution of interaction or reversal fields, and H c represents the distribution of switching or coercive fields. EXPERIMENT To demonstrate the utility of the FORC measurement and analysis protocol for characterizing hightemperature magnetic properties of mater
Data Loading...
