Magnetic core/shell-type composites composed of coarse FePt particles coated with finely powdered iron nitride. (October 2018)

• Record Type: Journal Article
• Authors: Yamauchi, Ryoji; Masubuchi, Yuji; Kikkawa, Shinichi
• Is Part Of: Materials research bulletin. Volume 106(2018)
• Page Start: 124
• Page End: 130
• Publication Date: 2018-10
• Subjects: Fe16N2 -- Magnetic hybrid -- Core-shell -- Hard magnetic material -- FePt; Materials -- Periodicals; Crystal growth -- Periodicals; Matériaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Crystal growth; Materials; Periodicals; 620.11
• DOI: 10.1016/j.materresbull.2018.06.001
• Languages: English
• ISSNs: 0025-5408

Abstract

Graphical abstract: Highlights: Magnetic core/shell-type composites were prepared on α″-Fe16 N2 -like compound with FePt core. α″-Fe16 N2 -like compound grew epitaxially on the FePt core. Magnetic coupling increased the magnetic coercivity of α″-Fe16 N2 -like compound. Abstract: Although α″-Fe16 N2 -like compounds exhibit enhanced magnetization compared to α-Fe, it is important to increase their magnetic coercivity to obtain new hard magnetic materials for electric vehicle application. In the present work, coarse FePt particles were coated with finely powdered Fe3 O4 produced by the hydrolysis of Fe(acac)3 in benzyl alcohol. This Fe3 O4 coating layer was subsequently reduced under hydrogen and then nitrided by ammonolysis at 150 °C to obtain a dual-phase mixture of an α″-Fe16 N2 -like compound (referred to herein as "α″-Fe16 N2 ") and residual α-Fe. The ("α″-Fe16 N2 " + α-Fe)1-x /(FePt)x composite particles for which x = 0.2, 0.4 or 0.6 generated smooth magnetization hysteresis curves, and the magnetic coercivity of these materials increased with increases in the proportion of FePt. Magnetic coupling was clearly evident between the core and shell regions in the composite powder for which x = 0.6, as demonstrated by a plot of the Wohlfarth interaction against the magnetic field. Transmission electron microscopy images confirmed magnetic coupling between the coarse FePt particles (several hundred nm in diameter) and the coating of fine mixed particles (several tens of nm in diameter) of "α″-Fe16 N2 " and α-Fe. The "α″-Fe16 N2 " crystals forming the particle shell were found to grow epitaxially, aligning their c -axes parallel to that of the tetragonal FePt.