T. Magn. Soc. Jpn. (Special Issues)., 1, 30-33 (2017)<Paper>Fabrication and magnetic properties of L 1 0 -MnGa highlyoriented thin films
Y. Takahashi, H. Makuta, T. Shima and M. Doi

Graduate School of Engineering, Tohoku Gakuin University, Tagajo 980-8573, Japan

L10-Mn-Ga highly oriented thin films were prepared on MgO (100) single crystalline substrates with a Cr buffer
layer using an ultra-high-vacuum electron beam vapor deposition system. All growths are monitored in real-timeusing reflection high-energy electron diffraction (RHEED). The RHEED pattern shows clear oriented growth. In
addition, XRD patterns for a fundamental (002) peak and (001) and (003) superlattice peaks were clearly observed.
Large magnetic anisotropy (Ku) of 10.5 Merg/cm3 and saturation magnetization (Ms) of 470 emu/cm3 were observedfor L10-Mn-Ga film (100 nm) at Ts = 300 ℃. When the thickness of L10-Mn-Ga decreased from 100nm to 5nm, Ku (=6.01 Merg/cm3), Ms (= 302 emu/cm3) and Ra (= 1.45 nm) were decreased, respectively.
Keywords: L10-Mn-Ga, magnetic anisotropy, saturation magnetization, electron beam evaporation method, thinfilm
1. Introduction
Mn-Ga alloy thin film is known to exhibit asaturation magnetization; Ms ~ 200-600 emu/cm3 [1, 2,5], a high magnetic anisotropy; Ku ~ 10-23.5 Merg/cm3[1], a high spin polarization; P ~ 88 % (it wastheoretically predicted to be a half-metallic-like
ferrimagnet) [3] and 58 % experimentally [4], and a low
Gilbert damping constant; α ~ 0.008-0.015 [1]. It has
been attractive attention as a new material for spinelectronics device [5-12]. Recently, thin films of ordered
Mn-Ga alloy is one of the most intensively studiedmaterials for a magnetic tunnel junction (MTJ) for thesuper gigabit (Gbit) class magnetic random accessmemory operated by spin transfer torque (STT-MRAM)[14-20]. The primary issue to be addressed in MRAM
applications is to reduce the critical current (Ic) required
for STT-induced magnetization switching. Therefore,
MTJ films should have a low Ms ~ 100 emu/cm3, a low α≦ 0.01, a high Ku ≧ 10 Merg/cm3, and a high P ≧70 %, Mn-Ga alloy thin film is very attractive to satisfy
these required properties [13]. In addition, the thicknessof the magnetic free layer in such STT device is required
to be below 5nm in general [10]. At the moment, little
has been reported on L10-MnGa thin film having a highperpendicular magnetic anisotropy (PMA) oriented
perpendicular to the substrate by using an ultra highvacuum electron beam (UHV-EB) vapor deposition
system.
In this paper, L10-MnGa highly oriented thin films
have been fabricated by using an UHV-EB vapor
deposition system and their magnetic properties ware
investigated.
2. Experimental procedure
Prior to film deposition, Mn1.0Ga target alloys wereprepared from high purity manganese (99.999 %) andgallium (99.9999 %) by arc melting method in argon
atmosphere. The base pressure of arc melting was less30

than 10-3 Pa. Mn-Ga thin films were prepared on MgO(100) single crystalline substrates with a Cr buffer layerusing an ultra-high-vacuum electron beam evaporation
system with a base pressure below 8.9×10-7	
  Pa. The
stacking structure of sample was follows: MgO (100)substrate/ Cr (5 nm)/ Mn-Ga (100-5 nm)/ Cr (10 nm).
The substrate was heated to Ta = 300 ℃ during
deposition and annealed at 300 ℃ (3 h) for improve thequality of crystal. The compositions of the films were
determined by an energy dispersive X-ray spectroscopy(EDX) and X = 77.8 (1st depo.), 71.5 (2nd depo.), 62.0
(3rd depo.), 69.9 (4th depo.), 59.3 (5th depo.) and 44.6
(6th depo.) for MnXGa100-X (at. %) are confirmed. All
growths are monitored in real-time using reflection
high-energy electron diffraction (RHEED). The crystal
structure of the samples was characterized by X-ray
diffraction (XRD) with the Cu Kα radiation line(a) MgO (100) sub.

[1] azimuth(e) X = 69.9

[11] azimuth

(b) Cr buffer[1] azimuth[11] azimuth(c) X = 77.8

[11] azimuth

[1] azimuth[11] azimuth(g) X = 59.3

[1] azimuth[11] azimuth

[1] azimuth[11] azimuth(d) X = 71.5

[1] azimuth

(f) X = 62.0

[1] azimuth[11] azimuth

[10 azimuth[11] azimuth(h) X = 44.6

Fig. 1. RHEED patterns for the substrate, bufferand MnXGa100-X thin films at Ts = 300 ℃. (a) MgO(100) sub., (b) Cr buffer, (c) 77.8, (d) 71.5, (e) 69.9, (f)62.0, (g) 59.3, (h) 44.6 with the electron beam azimuth[10] and [11] of MgO (100) substrate.

Transaction of the Magnetics Society of Japan (Special Issues) Vol.1, No.1, 2017

3

(a)

M (emu/cm )

Magnetization (emu/cm)
3

γ – Mn3Ga (003)



22 - Mn3Ga

(006)

 (112)



 D0

Cr 200(004) (002)

MgO snb.!

 (111)

(002)
 (110)

 (001)

Intensity (log. scale) L10 - MnGa

(b)
(c)
(d)
(e)
(f)

20

30

40

50

60

2 Theta (deg.)

70

80

90

Fig. 2.
XRD patterns for MnGa thin films
prepared on MgO (100) substrate at Ts = 300 ℃.
The Mn content X for MnXGa100-X films (100 nm) are(a) 77.8, (b) 71.5, (c) 69.9, (d) 62.0, (e) 59.3 and (f)44.6 (at. %).
(wavelength equal to 0.15418 nm). The surface
roughness of the film was investigated by atomic force
microscopy (AFM). The magnetic properties were
measured by using a superconducting quantum
interference device (SQUID) magnetometer in the field
up to ±70 kOe, and Ms and Ku for each thin film were
evaluated from magnetization curves.
3. Results and discussion
RHEED patterns of Cr buffer and the growth of
MnXGa100-X films (100 nm) with various Mn content
prepared on MgO (100) substrate are shown in Fig.1.
The Mn content was varied as follows: X = (a) 77.8, (b)71.5, (c) 69.9, (d) 62.0, (e) 59.3 and (f) 44.6 (at. %). The
MnXGa100-X films were fabricated from only Mn1.0Ga
target alloy. The RHEED pattern shows clear oriented
growth in c-plane, and the surface reconstruction
structure in Mn-Ga layer was clearly observed. It
should be noted that this oriented thin film exhibits aflat surface at the atomic level.
Since the composition is different by number ofdeposition by vapor pressure difference, Mn-Ga films
were confirmed that it is a L10 structure by using XRD.
XRD patterns for MnXGa100-X films with various Mn
content prepared on MgO (100) substrate are shown in
Fig. 2. The Mn content was varied as follows: X = (a)77.8, (b) 71.5, (c) 69.9, (d) 62.0, (e) 59.3 and (f) 44.6
(at. %). The intense peak from Cr buffer layer and MgOsubstrate ware clearly observed for all sample. In
addition, a fundamental (002) peak, (001) and (003)superlattice peaks of the L10-MnGa phase were clearlyobserved for X = 62.0 (at. %) (d) and X = 59.3 (at. %) (e).
Furthermore, both fundamental (004) and superlattice(002) and (006) peaks of the D022-Mn3Ga phase wereconfirmed at the X = 71.5 (at. %) (b). The chemical order

400
200
0
-200
-400
400
200
0
-200
-400
400
200
0
-200
-400

(a)

(d)

//

//
(e)

(b)

//

(c)

//

(f)

//

-60

-30

0

30

//

60 -60

-30

0

30

60

H (kOe)
Magnetic
field (kOe)
Fig. 3. Magnetization curves for MnGa thin films
prepared on MgO (100) substrate at Ts = 300 ℃. The
Mn content X for MnXGa100-X films (100 nm) are (a)77.8, (b) 71.5, (c) 69.9, (d) 62.0, (e) 59.3 and (f) 44.6
(at. %).
parameter S of X = 62.0 (at. %) (d) and X = 59.3 (at. %)(e) were shown S = 0.79 and 0.86. However, Mn-Ga thinfilm of X = 59.3 (at. %) (e) show decrease of (003)superlattice peak of the L10-MnGa phase. Therefore, the
Mn-Ga thin film of X = 62.0 (at. %) (d) shows best
preferred orientation of L10 structure.
Magnetization curves for the MnXGa100-X films
prepared on MgO (100) substrate are shown in Fig. 3.
All measurements were preformed at room temperature.
A magnetic field was applied perpendicular to the film
plane direction for the curves indicated by ⊥, and it wasapplied along the in-plane direction for those indicatedby //. Magnetization curve for X = 71.5 (at. %) (b) shows
the curve of the case of a typical D022 structure [2,12].
Moreover, Mn-Ga films of X = 62.0 (at. %) (d) and X =59.3 (at. %) (e) had relatively high Ms and low Hc. To
evaluate the PMA properties quantitatively, the Ku was(d) t = 20 nm

(a) MgO (100) sub.

[1] azimuth[11] azimuth

[1] azimuth[11] azimuth(c) t = 100 nm

[1] azimuth

[1] azimuth[11] azimuth(e) t = 10 nm

(b) Cr buffer[1] azimuth[11] azimuth

(f) t = 5 nm

[11] azimuth

[1] azimuth[11] azimuthFig. 4. RHEED patterns for the substrate, bufferand Mn62.0Ga38.0 (at %) thin films of different
thickness (tMn-Ga nm) at Ts = 300 ℃. (a) MgO (100)sub., (b) Cr buffer, (c) 100, (d)20, (e)10, (f)5 with theelectron beam azimuth [10] and [11] of MgO (100)substrate.

Transaction of the Magnetics Society of Japan (Special Issues) Vol.1, No.1, 201731 (002)

 (003)

(c)

70

80

(d)

(b)

200

//

//

0

-400
-60

90

Fig. 5. XRD patterns for Mn62.0Ga38.0 (at %)thin films of different thickness (tMn-Ga nm)
prepared on MgO (100) substrate. tMn-Ga of (a) 100,(b) 20, (c) 10 and (d) 5 at Ts = 300 ℃ and Ta =300 ℃ (3 h).
estimated using the relations Ku = Ms×Hkeff / 2 + 2πMs2.
Here, the effective anisotropy field (Hkeff) was defined as
the extrapolated intersection of the in-plane M-H curves
with the saturation magnetization value of out-of-plane
M-H curves. In Mn-Ga films of X = 71.5 (at. %) (b), X =62.0 (at. %) (d) and X = 59.3 (at. %) (e), Mn-Ga films
with high Ku ≧ 10 Merg/cm3 were obtained. Highest
Ms of 470 emu/cm3 and Ku of 10.5 Merg/cm3 wereconfirmed by epitaxial Mn-Ga film of X = 62.0 (at. %)(d).
RHEED patterns of Cr buffer and the growth of
Mn62.0Ga38.0 (at %) films of different thickness (tMn-Ganm) on MgO (100) substrate are shown in Fig.4, tMn-Ga is(c) 100, (b) 20, (c) 10 and (d) 5. The observed RHEED
patterns remain somehow bright and streaky. This
indicates that the films are highly crystalline and haverough surfaces except surfaces of tMn-Ga = 5 nm.
XRD patterns for Mn62.0Ga38.0 (at %) film of different
thickness (tMn-Ga nm) on MgO (100) substrate are shownin Fig.5. A fundamental peak, and superlattice peaks of
the L10-MnGa phase were clearly observed for the tMn-Ga= 100 nm. The tMn-Ga = 20 nm film shows clear
L10-MnGa (001), (002), (110) and (112) peaks (notshown (003)). The tMn-Ga = 10 and 5 nm films show
relatively small Mn-Ga (002), (110) and (112) peaks (notshown (001)). With decreasing thickness (100-5 nm), the
Mn-Ga films show shift of diffraction angle (superlattice
peaks are small). In addition, the chemical orderparameter S of the tMn-Ga = 20 nm film was shown S =0.57, it shows a significant decrease in the S comparedto the tMn-Ga = 100 nm (S = 0.78).
Magnetization curves for Mn62.0Ga38.0 (at %) thin filmsof different thickness (tMn-Ga nm) prepared on MgO (100)substrate are shown in Fig. 6. All measurements werepreformed at room temperature. The magnetic field was

32

//

-200

-30

0

30

60 -60-30

H (kOe)
Magnetic
field (kOe)

0

30

60

Fig. 6.
Magnetization curves for Mn62.0Ga38.0(at %) thin films of different thickness (tMn-Ga nm)
prepared on MgO (100) substrate. tMn-Ga of (a) 100,(b) 20, (c) 10 and (d) 5 at Ts = 300 ℃ and Ta =300 ℃ (3 h).
(a)!   

 (b)!    (c)!   

 (d)!  

1 μm

1 μm

1 μm

1 μm



Fig. 7. AFM images for Mn62.0Ga38.0 (at %) thinfilms of different thickness (tMn-Ga nm) prepared on
MgO (100) substrate. tMn-Ga of (a) 100, (b) 20, (c) 10
and (d) 5 at Ts = 300 ℃ and Ta = 300 ℃ (3 h).
M (emu/cm3)

60

400

500
400
300

Ku (Merg/cm3)

50

2 Theta (deg.)010

Ra (nm)

40

//

-400

(a)
(b)

30

(c)

-200

(d)

20

(a)

200

3

3) cm )Magnetization(emu/
M (emu/cm

 (112)
Cr 200

MgO snb.!
 (110)

 (001)

Intensity (log. scale)400

 L10 - MnGa

8
6
6
4
2
0

0

20

40

60

tMn-Ga (nm)

80

100

Fig. 8. Ms, Ku and Ra as function of tMn-Ga (nm)for Mn62.0Ga38.0 (at %) thin films prepared on MgO(100) substrate at Ts = 300 ℃, Ta = 300 ℃ (3 h).

Transaction of the Magnetics Society of Japan (Special Issues) Vol.1, No.1, 2017

applied in the perpendicular (⊥) and in-plane (//)
directions to the film. The easy magnetization axis isaligned perpendicular to the film plane for all thesamples. With decreasing thickness (100-5 nm), Ms (=520-302 emu/cm3) and Ku (10.0-6.01 Merg/cm3) weredecreased. It can be considered that decreasing Ms and
Ku originated primary from the decreased of chemicalorder parameter S. Furthermore, AFM images for
Mn62.0Ga38.0 (at %) thin films of different thickness(tMn-Ga nm) prepared on MgO (100) substrate are shownin Fig. 7. The average roughness (Ra) for the Mn-Ga
surfaces (tMn-Ga = 100, 20, 10 and 5 nm) was found to be
Ra = 5.25, 4.74, 2.52 and 1.33 nm, respectively. Withdecreasing thickness (100-5 nm), Ra (= 5.25-1.33 nm)
was decreased. The Ms, Ku and Ra as function of tMn-Ga(nm) for Mn-Ga thin films are summarized in Fig.8.
Considering that the growth temperature of PMA film
should be as low possible for practical applications in
spintronic devices, the L10-Mn-Ga highly oriented thinfilm is very promising because high PMA can beobtained at relative low growth temperature at Ts =300 ℃ and Ta = 300 ℃ in this study.
4. Summary
Mn-Ga thin films have been fabricated by using
UHV-EB vapor deposition and their magnetic properties
were investigated. Variation of Mn composition has
been confirmed by number of deposition. The clear
oriented growth of Mn-Ga films has been confirmed on
MgO (001) substrate by using RHEED in real time.
Large Ms of 470 emu/cm3 and Ku of 10.5 Merg/cm3 wereobtained for L10-Mn-Ga highly oriented thin film. Withdecreasing the thickness (100-5 nm), Ms (= 302
emu/cm3), Ku (= 6.01 Merg/cm3) and Ra (= 1.45 nm) weredecreased. The L10-Mn-Ga highly oriented thin film is
considered to be promising because relative high Ku andlow Ms can be obtained at relatively low growthtemperature at Ts = Ta = 300 ℃.
Acknowledgements This work was supported inpart by the Ministry of Education, Culture, Sports,
Science and Technology project for the “Hi-TechResearch Center Preparation Program” and performedat the Hi-tech Research Center of Tohoku Gakuin
University. Part of this work was supported by“Collaborative Research Based on Industrial Demand”
program from Japan Science and technology Agency.

References
1)
2)
3)
4)
5)
6)
7)

8)
9)
10)
11)
12)
13)

14)
15)
16)

17)
18)
19)
20)

S. Mizukami, T. Kubota, F. Wu, X. Zhang, T. Miyazaki, H.
Naganuma, M. Oogane, A. Sakuma, and Y. Ando: Phys.
Rev. B, 85, 014416 (2012).
F. Wu, S. Mizukami, D. Watanabe, H. Naganuma, M.
Oogane, Y. Ando and T. Miyazaki: Appl. Phys. Lett., 94,
122503 (2009).
B. Balke, G. H. Fecher, J. Winterlik and C. Felser: Appl.
Phys. Lett., 90, 152504 (2007).
H. Kurt, K. Rode, M. Venkatesan, P. Stamenov and J. M.
D. Coey: Phys. Rev. B, 83, 020405R (2011).
A. Köhler, I. Knez, D. Ebke, C. Felser and S. S. P. Parkin:Appl. Phys. Lett., 103, 162406 (2013).
S. Mizukami, A. Sakuma, A. Sugihara, T. Kubota, Y.
Kondo, H. Tsuchiura and T. Miyazaki: Appl. Phys.
Express, 6, 123002 (2013).
A. Sugihara, K. Z. Suzuki, T. Miyazaki and S. Mizukami:
J. Appl. Phys., 117, 17B511 (2015).A. Köhler, I. Knez, D.
Ebke, C. Felser and S. S. P. Parkin: Appl. Phys. Lett., 103,
162406 (2013).
T. Kubota, S, Ouardi, S. Mizukami, G. H. Fecher, C.
Felser, Y. Ando and T. Miyazaki: J. Appl. Phys., 113,
17C723 (2013).
A. Sugihara, S. Mizukami, Y. Yamada, K. Koike and T.
Miyazaki: Appl. Phys. Lett., 104, 132404 (2014).
K. Z. Suzuki, R. Ranjbar, A. Sugihara, T. Miyazaki and S.
Mizukami: Jpn. J. Appl. Phys., 55, 010305 (2016).
Q. L. Ma, T. Kubota, S. Mizukami, X. M. Zhang, H.
Naganuma, M. Oogane, Y. Ando and T. Miyazaki: Appl.
Phys. Lett., 101, 032402 (2012).
W. Y. Zhang, P. Kharel, S. Valloppilly, R. Skomski and D.
J. Sellmyer: J. Appl. Phys., 117, 17E306 (2015).
H. Yoda, T. Kishi, T. Nagase, M. Yoshikawa, K.
Nishiyama, E. Kitagawa, T. Daibou, M. Amano, N.
Shimomura, S. Takahashi, T. Kai, M. Nakayama, H.
Aikawa, S. Ikegawa, M. Nagamine, J. Ozeki, S. Mizukami,
M. Oogane, Y. Ando, S. Yuasa, K. Yakushiji, H. Kubota, Y.
Suzuki, Y. Nakatani, T. Miyazaki, and K. Ando: Curr.
Appl. Phys., 10, e87 (2010).
H. Lee, H. Sukegawa, J. Liu, T. Ohkubo, S. Kasai, S.
Mitani and K. Hoho: Appl. Phys. Lett., 107, 032403(2015).
J. Winterlik, B. Bake, G. H. Fecher, M. C. M. Alves, F.
Bernardi and J. Morais: Phys. Rev. B, 77, 054406 (2008).
S. Mizukami, F. Wu, A. Sakuma, J. Walowski, D.
Watanabe, T. Kubota, X. Zhang, H. Naganuma, M.
Oogane, Y. Ando and T. Miyazaki: Phys. Rev. Lett., 106,
117201 (2011).
Z. Bai, Y. Cai, L. Shen, M. Yang, V. Ko, G. Han and Y.
Feng: Appl. Phys. Lett, 100, 022408 (2012).
M. Glas, D. Ebke, I. M. Imort, P. Thomas and G. Reiss: J.
Magn. Mater., 333, 134 (2013).
M. Li, X. Jiang, M. G. Samant, C. Felser and S. S. P.
Parkin: Appl. Phys. Lett., 103, 032410 (2013).
Y. Miura and M. Shirai: IEEE Trans. Magn., 50, 1400504(2014).

Received Oct. 10, 2016;
Accepted Mar. 06, 2017

RevisedTransaction of the Magnetics Society of Japan (Special Issues) Vol.1, No.1, 2017

Dec.

26,

2016;

33