Permanent Magnet Nanoflakes Jinfang Liu llaborators: ozhi Cui and Melania Marinescu, Electron Energy Corporation ex Gabay and George Hadjipanayis, University of Delaware Electron Energy Corporation, Landisville, PA, USA [email protected]presentation for Workshop on Amorphous and Nanostructured Magnetic Materials Iasi, Romania September 2011
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Permanent Magnet Nanoflakes
Jinfang Liu
Collaborators: Baozhi Cui and Melania Marinescu, Electron Energy CorporationAlex Gabay and George Hadjipanayis, University of Delaware
Room-temperature intrinsic magnetic properties of bulk RCo5 (R = Sm, Y), Sm2Co17 and Nd2Fe14B
High HA High Tc High Ms
11 IntroductionIntroduction
●Microparticles, nanoparticles, ribbons, thin films of the Sm-Co, Pr-Co and Nd-Fe-B compounds have been produced by ball-milling, melt-spinning, and magnetron sputtering.
●The use of surfactants during ball milling influences not only the size of the particles, but also their shape. Flakes of malleable metals and alloys like Ni, Cu, Fe-Co, Fe-Co-Zr, Fe-Si-Al, Sn-Ag-Cu, have been fabricated by surfactant-assisted ball milling.
●However, SmCo5 and Nd2Fe14B magnetic materials are brittle in nature and, therefore, they are not expected to "flake" during ball milling.
●This talk will report on the unusual formation mechanism, optimization and the role of surfactants to form textured SmCo5 and Nd2Fe14B flakes by surfactant-assisted high energy ball milling (HEBM).
Shapes of rare-earth-based magnetic materials
Sm17Co83 or Nd15.5Fe78.5B6 (at.%) ingots
One-step high energy ball milling (HEBM)
SmCo5 or Nd2Fe14B flakes
XRD, SEM, TEM, VSM
SmCo5 or Nd2Fe14Bnanoparticles(after HEBM with OA for 4 - 8 h); < 1 wt.%
Flake thickness and length, values of intensity ratio I002/I111 and average grain size
of the SmCo5 phase for the as-milled SmCo5 flakes.
Effect of milling time on flake dimension, grain size and texture
isotropic: 0.19HEBM in heptane with 15 wt.% OA
Nan
ofla
kes
● As the milling time increases, the flake thickness becomes smaller and the texture of the flakes decreases.
SEM images of magnetically aligned SmCo5 single-crystal submicron flakes and
textured nanoflakes prepared by HEBM in heptane with 15 wt.% OA for (a) 3, and (b) 6 h. The arrow bars show the applied magnetic field directions.
Alignment in magnetic field of SmCo5 flakes
Milling time
(a) 3 h
(b) 6 h
Effect of milling time on texture
● Distribution intensities of [001] out-of-plane texture component of SmCo5 are 19.0, 6.0, and 4.1 times the random value, in magnetically aligned SmCo5 submicron flakes and nanoflakes prepared by HEBM in heptane with 15 wt.% OA for (a) 3, (b) 5, and (c) 8 h. (a) non- aligned, (b) aligned in 1.9 T
(a) Single-crystal SmCo5 flake (t ≤ 3 h);
(b) Polycrystalline flake with small-angle grain boundaries (t = 3–4 h). The dashed lines marked the orientations (~6.5o) and the arrows reveal the grain boundary. Grain size ~ 20 nm.
Anisotropic magnetic behavior As-milled samples aligned in 1.9 T
●Morphology of the SmCo5 nanoflakes can be efficiently controlled by the amount of surfactant (oleic acid) : “kebab-like” morphology and well-separated flakes are observed.
●SEM images are obtained after HEBM in heptane + OA for 5 h.
0 wt.% OA 15 wt.% OA 150 wt.% OA40 wt.% OA
Effect of amount of oleic acid on sample morphology
B.Z. Cui, A.M. Gabay, W. F. Li, M. Marinescu, J. F. Liu, and G.C. Hadjipanayis,
J. Appl. Phys. 107, 09A721 (2010).
●Variation of the amount of OA between 15 and 150 wt.% has little effect on the magnetic properties those are distinctly anisotropic. Coercivities: ~ 17-18 kOe.
15 wt.% OA
Effect of amount of oleic acid on magnetic properties
SmCo5 nanoflakes milled in heptane with OA and OY
30 wt.% OA, 5 h 30 wt.% OY, 5 h
There is little difference in morphology between the flakes prepared by HEBM for 5 h in heptane with 30 wt.% oleic acid (OA) and oleylamine (OY).SmCo5 nanoflakes have a length of about 0.5-10 μm and a thickness of 8 to 80 nm.
Effect of different surfactants on morphology of SmCo5 nanoflakes
SmCo5 powders milled in heptane with TOA (Trioctylamine)
30 wt.%, 5 h
100 wt.%, 5 h60 wt.%, 2.5 h
SmCo5 textured nanoflakes with thickness of 80-200 nm SmCo5 irregular particles
(nearly isotropic)
SmCo5 textured nanoflakes with thickness of 50-150 nm
Effect of different surfactants on morphology of SmCo5 nanoflakes
A higher amount of TOA ( ≥ 40 wt.%) is required to obtain textured SmCo5 nanoflakes, compared with OA and OY.
The flakes preserve SmCo5 structure and have a [001] texture. With increasing the milling time from 3 to 6 h, the average grain size decreased from 21 to 15 nm.
Coercivity of the as-milled SmCo5 flakes increased first and then decreased after reaching a maximum value of 16 kOe after milling for 5 h.
Structure and magnetic properties of SmCo5 nanoflakes by HEBM in heptane with 30 wt.% OA
Structure and magnetic properties of SmCo5 nanoflakes by HEBM in heptane with 30 wt.% OY
The flakes preserve SmCo5 structure and have a [001] texture. With increasing the milling time from 3 to 6 h, the average grain size decreased from 21 to 10 nm
Coercivity of the as-milled SmCo5 flakes increased first and then decreased after reaching a maximum value of 15.0 kOe after milling for 5 h.
When the amount of TOA was 100 wt.%, both the texture and coercivity decreased with milling time from 2.5 to 6.5 h.
iHc = 15.8 kOe after milled for 2 h.
Structure and magnetic properties of SmCo5 nanoflakes by HEBM in heptane with 100 wt.% TOA
(a) 0.25,
(b) 1 h,
(c) 2 h,
(d) 3 h,
(e) 5 h
Sample morphology for different milling time in heptane with 40 wt.% OA
● The effects of OA and OY were found to be very similar.
● DyF3 was markedly less efficient to providing formation of thin anisotropic Nd2Fe14B flakes. We did not observe any additional magnetic hardening after using the DyF3 additive.
►The effect of different surfactants, such as OA, OY and DyF3 (which is expected to inhibit cold-welding similarly to the "true" surfactants)
OA OY DyF3
Thickness (nm) 80 - 160 80 - 180 800 - 6000
Length (μm) 0.5 – 10.0 0.5 – 10.0 1 - 40
Hc (kOe) 3.5 3.7 3.2
40% OA, 5 h HEBM 40% DyF3, 5 h HEBM20% OY, 5 h HEBM
Ball-milling
time (h)
Flake
thickness
(nm)
Flake length
(mm)
I006/I105Average grain
size
(nm)
0 - 1 - 100*-
-
0.25 2000 - 4000 1 - 3340
-
0.5 600 - 1800 1 - 3039
-
1 300 - 1650 1 - 1636
-
2 250 - 980 1 - 1434
-
3 200 - 440 1 - 1413
-
4 90 - 360 1 - 1314
14
5 80 - 180 0.5 - 108
10
6 40 - 110 0.5 - 106
10
Flake thickness and length, intensity ratio of I006/I105 and average grain sizes of
the Nd2Fe14B hard phase for the as-milled Nd2Fe14B flakes. *: particle size.
HEBM in heptane + 40 wt.% OA
isotropic: 0.5
Effect of milling time on flake dimension, grain size and textureN
●The crystalline anisotropy weakens after prolonged milling.
Basal cleavage planes: (001) SmCo5 or (110) Nd2Fe14B
XRD patterns and M-H curves of Nd2Fe14B (a) single-crystal submicron flakes and (b) textured poly-nanocrystalline flakes prepared by HEBM in heptane with 40 wt.% OA for (a) 2 h, and(b) 5 h.
Crystallographically and magnetically anisotropic behaviorof Nd2Fe14B flakes
Evolution of coercivity and texture in Nd2Fe14B flakes via surfactant-assisted HEBM
For the as-milled textured Nd2Fe14B flakes, the major problem was the low iHc ≤ 3.7 kOe. Efforts to increase iHc :
►Introduction of low melting-point Nd70Cu30 and Pr68Cu32 additives (eutectic alloys) during the surfactant-assisted HEBM process.
►Post-annealing of the as-milled Nd2Fe14B flakes.
►Nd14Dy1.5Fe78.5B6 rather than the Nd15.5Fe78.5B6 alloys
● When milled together with Nd70Cu30 or Pr68Cu32 powders (Tmelt = 520 or 472oC ), the as-milled Nd15.5Fe78.5B6 nanoflakes exhibited an increase in Hc, from 3.7 to 4.7 kOe by an addition of extra 20 wt% of Nd70Cu30.
● The Hc can be further increased to 6.8 kOe by annealing at 450oC for 30 min.
● The additives of Nd70Cu30 and Pr68Cu32
have very similar effect on morphology and magnetic properties for both as-milled and annealed Nd2Fe14B flakes.
Effect of additives and annealing on magnetic properties of Nd2Fe14B flakes
-20 -10 0 10 20
-100
-50
0
50
100 // aligned
7.0 kOe
Nd14
Dy1.5
Fe78.5
B6
+ 20 wt.% Nd70
Cu30
Nd14
Dy1.5
Fe78.5
B6
+ 20 wt.% Pr68
Cu32
HEBM for 5 h in
heptane + 20 wt.% OY
then, annealed at 450oC
for 30 min7.0 kOe
M (
emu/
g)
H (kOe)
Nd15.5Fe78.5B6 + extra 20 wt.% Nd70Cu30 ingot powders, HEBM for 5 h in heptane + 20 wt.% OY
-20 -10 0 10 20-90
-60
-30
0
30
60
90 Magnetic AnisotropyAnnealed at 450oC for 30 min
Nd15.5
Fe78.5
B6
+ 20 wt.% Nd70
Cu30
flakes by HEBM for 5 h inheptane + 20 wt.% OY
M (
emu/
g)
H (kOe)
//, 6.8 kOe
, 6.9 kOe
-20 -10 0 10 20-100
-50
0
50
100 Magnetic Anisotropy
3.9 kOe
//
4.7 kOe
M (
emu/
g)
H (kOe)
Annealed at 450oC for 30 min
A mixture of nanocrystalline Nd2Fe14B and disordered Nd-(Cu) rich phases at grain boundary in one annealed flake
One flake of Nd2Fe14B+Nd70Cu30 (EDS)Element Weight % Atomic %---------------------------------------------- NdL 52.1 29.9 FeK 43.0 63.7 CuK 4.9 6.4 Total 100.0 100.0
● SmCo5 and Nd2Fe14B single-crystal submicron flakes and textured poly-nanocrystalline nanoflakes were fabricated by one-step surfactant-assisted HEBM.
● Surfactants play an essential role in the formation of anisotropic flakes by a decrease of cold welding and agglomeration of the flakes. OA and OY have similar effects on the formation of anisotropic flakes. A higher amount of TOA is required to obtain nanoflakes.
● Both the addition of a low melting-point Nd70Cu30 or Pr68Cu32 alloys and a proper post-annealing treatment can increase the coercivity of Nd2Fe14B nanoflakes.
● These novel flakes have unique properties, including a high degree of texture, a high stability in air and a unique shape that can be easily coated.
● Possible applications of the hard magnetic flakes include anisotropic nanocomposite magnets with high energy product, laminated magnets with reduced eddy current loss, etc.