Abstract
The microstructure and magnetic properties of Nd7Fe67B22Mo3.5-xZr0.5Tix (x = 0, 0.5, 1.0) nanocomposite magnets prepared by annealing the amorphous precursors have been investigated and presented. The Nd7Fe67B22Mo3Zr0.5Ti0.5 alloy exhibits high glass forming ability as well as good hard magnetic properties in magnetic rods of 2 mm in diameter and 40 mm in length. As-cast Nd7Fe67B22Mo3Zr0.5Ti0.5 amorphous rod shows soft magnetic properties. Annealing induces promising hard magnetic properties as Br = 0.55 T, iHc = 965 kA/m and (BH)max = 47.6 kJ/m3. Electron microscopy elucidates a microstructure composed of magnetically soft α-Fe (27 nm), Fe3B (24 nm) and hard Nd2Fe14B (50 nm) magnetic grains. The single phase hard magnetic characteristics of M-H loop and δM curve yield the existence of strong exchange coupling interactions between the magnetically soft and hard phases.
Highlights
Rare earth nanocomposite Nd2Fe14B (Pr2Fe14B)/α-Fe (Fe3B) magnets have attracted considerable attention due to expected high maximum energy product and unique microstructure compared to single-phase Nd2Fe14B magnets.[1,2,3] Nanocomposite Nd2Fe14B (Pr2Fe14B)/α-Fe (Fe3B) magnets can be produced through directly mold casting or annealing the amorphous precursors prepared through copper mold casting technique.[4,5] Copper mold injection casting technique is economical and facile to produce bulk nanocomposite magnets in rods, sheets and foils.[6,7,8] The major challenge with this technique is to enlarge the magnet size with good hard magnetic properties
Studies have shown that large size magnetic rods can be obtained through increasing the glass forming ability (GFA) by element addition to Nd
The Ti-free Nd7Fe67B22Mo3.5Zr0.5 alloy displays a dual phase structure consisting of major amorphous phase and minor crystalline phase, while 0.5 at.% Ti containing alloy shows a broad hump in the XRD pattern representing a single amorphous structure. This implies that proper amount of Ti addition can enhance the glass forming ability (GFA) for the Nd7Fe67B22Mo3.5-xZr0.5Tix alloy system
Summary
Rare earth nanocomposite Nd2Fe14B (Pr2Fe14B)/α-Fe (Fe3B) magnets have attracted considerable attention due to expected high maximum energy product and unique microstructure compared to single-phase Nd2Fe14B magnets.[1,2,3] Nanocomposite Nd2Fe14B (Pr2Fe14B)/α-Fe (Fe3B) magnets can be produced through directly mold casting or annealing the amorphous precursors prepared through copper mold casting technique.[4,5] Copper mold injection casting technique is economical and facile to produce bulk nanocomposite magnets in rods, sheets and foils.[6,7,8] The major challenge with this technique is to enlarge the magnet size with good hard magnetic properties. The magnetic properties of nanocomposite magnets rely on exchange coupled magnetically soft (α-Fe, Fe3B) and hard (Nd2Fe14B) phases present in the microstructure. We have developed Nd-Fe-B-Mo-Zr nanocomposite rod magnets by copper mold casting and subsequent annealing.[15] As a result, it is of interest to find out whether the alloy enriched with Ti element is helpful to improve magnetic properties in large size magnetic rods or not. Based on this expectation, Nd7Fe67B22Mo3.5-xZr0.5Tix (x = 0, 0.5, 1.0 at.%) alloys were selected for the present study by considering previous experimentations and literatures.[16,17,18,19] Nanocomposite Nd7Fe67B22Mo3.5-xZr0.5Tix (x = 0, 0.5, 1.0 at.%) magnetic rods were prepared by copper mold casting and subsequent annealing. The exchange coupling effects between magnetically soft and hard phases were evidenced by the δM curves
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