Microstructure and Damping in FeTiN and CoFe films · resonance field. A plot for a sample with...

Microstructure and Damping inFeTiN and CoFe films

James Rantschler, Yunfei Ding, Soon-Cheon Byeon and Chester Alexander, Jr.,

Department of Physics and Astronomy and the Center for Materials for Information Technology, University of Alabama, 35487-0209.

This work was sponsored in part by the National Institute of Standards and Technology’s Nanotechnology Initiative, Contract # 43RANB1B1604, from Seagate Research, and from the University of Alabama MINT Center. We also acknowledge the CoFe samples supplied to us by Hong- Sik Jung.

Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering Center

Introduction

This study was carried out to look for relationships between damping in ferromagnetic films and magnetostriction or microstructure. Sputtered films of FeTiN, CoFe and CuCoFe were prepared and characterized by FMR, XRD, XPS, and magnetostriction measurements, to examine these possible relationships. The FMR studies have been carried out at multiplefrequencies to determine the intrinsic damping constant, α, and the extrinsic damping constant, ∆H0, as well as values of the anisotropy field Hk, the gyromagnetic ratio, γ, and the saturation magnetization value 4πMs.


Ferromagnetic resonance (FMR) studies were used to determine the values of Hk, 4πMs and the gyromagnetic ratio, γ, by rotating the sample in the plane of the films to determine the Hk value ((HHA – HEA)/2), and then finding the 4πMs and γ values from a fit to

for a plot of the square of the resonance frequency against the resonance field. A plot for a sample with 6.1% N is shown in Fig. 1.Values of Hk, 4πMs and γ, determined for a range of films with different N content are given in Table I.

.

))(4( ksk HHMHHf +++= πγ


FMR Determination of 4πMs, Hk and γ

The frequency dependent part is a good measure of the intrinsic or viscous damping described by α in the Landau-Lifshitz-Gilbert equation, whereas the extrinsic term ∆H0 is thought to be related to magnetic inhomogeneties (2). A graph of the FMR linewidthversus frequency for a sample with 6% nitrogen is shown in Fig. 2.Values of ∆H0 and α were determined by fits to these data and the results for FeTiN films with a range of nitrogen content areshown in Table I.

FMR Determination of α and ∆H0Previous investigators (1)have shown that the FMR linewidth∆H can be related to the damping and can be expressed as

γαfHH 20 +∆=∆


0

20

40

60

80

100

120

140

0 5 109 1 10101.5 10102 10102.5 10103 10103.5 1010

Line

wid

th ∆

H1/

2 (Oe)

Frequency (Hz)

FMR Data for FeTiN with 6% N

4πMs = 16371 Oeγ = 2.95 MHz/OeHk = 11 Oe

0

2 1020

4 1020

6 1020

8 1020

1 1021

1.2 1021

0 1000 2000 3000 4000 5000 6000 7000Fr

eque

ncy2 (H

z 2 )

Field (Oe)

∆H0 = 16 Oeα = 0.0047

Figure 1. Figure 2. Center For Materials For Information Technology

An NSF Materials Research Science and Engineering Center

TEM and Grain Size for FeTiN

Glass/FeTiN 50nm

0% N2

1cm scale=87nm

22.2 ± 6 nm

Glass/FeTiN 50nm

6% N2

1cm scale=87nm

9.6 ± 2.5 nm


5

10

15

20

25

30

-1 0 1 2 3 4 5 6 7

Gra

in S

ize

(nm

)

at. %NCenter For Materials For Information Technology

An NSF Materials Research Science and Engineering Center

Grain Size and Nitrogen Content in FeTiN Films

Exchange length calculations for FeTiN and CoFe, using

22 sex M

ALπ

=

give Lex = 4 nm for FeTiN

and Lex = 3 nm for CoFe

∆H0 values versus Grain Size for FeTiN and Cu/CoFe

0

50

100

150

200

0

100

200

300

400

500

600

0 10 20 30 40 50 60

∆ H0 (O

e)∆H

0 (Oe)

Grain Size (nm)

CoFe

FeTiN



Linewidths and ∆H0 for CoFe and Cu/CoFe

0

20

40

60

80

100

120

500

520

540

560

580

600

0 5 10 9 1 10 101.5 10 102 10 102.5 10 103 10 103.5 10 10

Lin

ewid

th ∆ H

1/2 (

Oe)

Frequency (Hz)

Lin

ewid

th ∆ H

1/2 (

Oe)Cu/CoFe

CoFe


%Nitrogen 4πMs (Oe)

Hk(Oe)

γ ( MHz/Oe)

∆H0( Oe)

α λ(x 10-6)

Grain size(nm)

0 19523 0 2.90 164 .005 -7 28

1.5 16951 7 3.05 53 .007 3 20

4.2 16800 10 2.99 32 .005 12 15

6.1 16371 11 2.95 16 .005 15 9

CoFe 23250 3.1 525 90 50

Cu/CoFe 23210 28 2.93 28 0.004 90 9

Microstructure and Magnetic Properties of FeTiN and CoFe

We observe no variation in the intrinsic damping constant α as a function of microstructure in FeTiN samples, but we do find that the parameter ∆H0 depends strongly on the size of grains relative to the exchange length: as the grain size approaches the exchange length, ∆H0 decreases. In CoFe samples we find the same ∆H0 vs. grain size relationship, but no observation of an α and microstructure relationship was possible because the intrinsic damping was obscured by the extrinsic linewidth for the CoFe sample. Our results are consistent with the results of Celinski and Henrich for amorphous and ultrathin samples (3). We observe no plausible relationship between magnetostriction and either the intrinsic or extrinsic damping parameters in either FeTiN or Cu/CoFe films.

Conclusions


References1. For example, see: T. D. Rossing, J. Appl. Phys. 34, 995 (1963); M. L. Spano,

et. al., J. Magn.Magn. Mater. 24,143 (1881); L. Kraus, et. al. Phys. Status Solidi 64, 449 (1981), J. F. Cochran, et. al. J. Appl. Phys. 53, 2261 (1982),

2. B. Henrich, J.F. Cochran, and R. Hasegawa, J. Appl. Phys. 57, 3690 (1985).

3. Z. Celinski and B. Henrich, J. Appl. Phys. 70, 5935 (1991).


Microstructure and Damping in FeTiN and CoFe films · resonance field. A plot for a sample with...

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