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Magnetic and transport properties of SiMn films with
the high Mn content Aronzon B.A.
Rylkov V.V.Tugushev V.V. Nikolaev S.N..Perov N.S.Semisalova A.
S. Caprara
Podolskii V.V.Lesnikov V.P.
A. Lashkul
RRC “Kurchatov Institute”, Moscow, Russia
NIFTI, N. Novgorod , Russia
Dipartamento di Fisica, Universita di Roma
Lappeenranta University of Technology, Finland
Moscow State University, Russia
PRB, 84, 075209 (2011)
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Outline1 Introduction. What is known about SiMn structures?
2 Transport, AHE
3 Magnetic properties
4 Model
5 Conclusion
The equilibrium solubility of Mn in Si is very low (~1016 cm-3). It is needed to reach higher manganese concentration (1021cm-3). Mn impurities in Si favor interstitial position and act as donors, that results in very weak exchange interaction.
While strong hybridization of Mn 3d states with s,p states in Si occurs if Mn enter substitutional (MnSi) positions as
acceptorsBinary compounds of 3d metals with Si are weak itinerant magnets of helicoidal type with Curie temperature <50K (no hysteresis loop).
MnxSi1-x
Si Si
Mn
Mn
1. Ion beam implantation Mn (х ≈ 0.8 %) : Tc > 400 K (M. Bolduc et al., Phys. Rev. B 71, 033302 (2005)).
Magnetism is due to paramagnetic defects T. Dubroca et al., Appl. Phys. Lett. 88, 182504
(2006); A.F. Orlov, A.B. Granovsky et al. JETP 109, 602 (2009)
2. Magnetron sputtering. (х ~ 5%): ТС ≈ 250К (X.C. Liu, Z.H. Lu et al., J. Appl. Phys. 100, 073903 (2006); 102, 033902 (2007)), p ≈1016cm-3
3. MBE [Si(20Å)/Mn(1 - 2Å)] (х ~ 5-10%):ТС ≈ 300К (S.H. Chiu et al., J. Appl. Phys. 103, 07D110 (2008)). While (х<17,5%):ТС ≈ 3К (L. Zeng, PRB, 77, 073306 (2008)) Magnetiztion; no AHE.
4. Magnetron co-sputtering. Mn-doped amorphous Si:H (х ~ 10 %):Т ≈ 150К (J.H. Yao, S.C. Li et al., Appl. Phys. Lett. 94, 072507 (2009)).
5. Mn –Si complexes (2-3) B/Mn (Q. Liu et al. Phys. Rev. B 77, 245211 (2008)) and self- organized in Si1-xMnx molecular clusters (S. Zhou et al. PRB 75, 085203 (2007); 80, 174423 (2009)) (> 0.2 B/Mn)
Mn4Si7 ТС ≈ 50К (A. Sulpice et al., JMMM. 272-276, 519 (2004)).
What is known about magnetic properties of MnxSi1-x
Method: Anomalous Hall Effect
The Hall resistance RHd= yx = R0B + RsMR0 and Rs are the ordinary and anomalous Hall coefficients.
Anomalous Hall Effect is proportional to magnetization. Two types of mechanisms:
skew –scattering - Rs Rxx and side-jump - Rs R2xx
For both mechanisms AHE depends on the strength of the spin-orbit interaction and spin polarization of carriers. The sign of either of the two contributions can be positive or negative depending on an interplay between the orientations of orbital and spin momenta as well as on the character (repulsive vs. attractive) of scattering potentials.[T. Dietl (2007)]
AHE current arises because the impuritycross-section seen by beam of electronspossesses right-left asymmetry
T. Jungwirth et al.(2006), T. Dietl et al.(2003), S.Y. Liu et al. (2005), V.K. Dugaev et al. (2005)
v(k) = grad [ε(k)]/h + (e/h)E(k)z(k) = 2Im[<u/ky|u/kx>] - does not depend on scattering
Why Anomalous Hall Effect ?
AHE depends on the strength of the spin-orbit interaction and spin polarization of carriers
AHE is not affected by the magnetism of substrate
AHE mainly is not affected by the inclusion of second phase
AHE is not need an expensive equipment and could be measured easily
Samples number/substrate
Rxx(77K)/Rxx(290K)
Growth temperature, Tg °C
d, nm Hc- coercitivity at 80
K (Oe)
AHEsign
Nо1Al2O3
0.94 300 40 2900-
Nо2Al2O3
0.93 300 57 2000-
Nо3Al2O3
0.85 350 55 4200-
№4GaAs
0.85 300 80 0 +
№5GaAs
0.84 300 50 0 +
№6GaAs
0.97 200 75 330+
№7GaAs
0.89 300 300 650-
Parameters of MnxSi1-x samples, x ≈ 0.35
Hole concentration p ≈ (2 – 3)1022 cm-3
2 4 6 80
500
1000
1500
2000C
ount
s
Energy, keV
Mn-L Si-K
Mn-K
GaAs substrate
EDAX ZAF Quantification Standardless SEC Table : Default
Microanalysis Report
-2 0 2-0.04
0.00
0.04
RH,
B,T
5 K100K
77K
The Hall resistance is determined mainly by the anomalous component even at room temperature and has negative sign while normal Hall effect is positive.
Hysteresis is observed up to 230 К.Hole concentration obtained from the normal Hall effect p 21022 cm-3.
Rs 2.410-8 Ohmcm/Gs (10-7 Ohmcm/Gs for GaMnAs with p 1021 cm-
3, S.H. Chun, et al., Phys. Rev. Lett. 98, 026601 (2007) ).
Anomalous Hall effect up to room temperature
-0.7 0.0 0.7
-0.03
0.00
0.03
300K
Ra H,
B, T
77K
230K
AHE ofstrongly doped SiMn.
Maximum Tc of
MnSi silicides not exceed 50 K. Hall resistance
0 50 100 150 200 250 3000.4
0.5
0.6
0.7
0.8
0.9
1.0
3
2
Rxx
(T)/
Rxx
(29
0K
)
T, K
1
The growth temperature:
1, 2, 2', 7, 11 - 300 oC; 3- 350 oC, 12-530 oC
2'
7
12
11
U. Gottlieb at el., JMMM (2004) and
Our results
Comparison with Mn4Si7
Comparison with (Si:H)Mn
-0.7 0.0 0.7
-0.03
0.00
0.03
-0.7 0.0 0.7
-0.004
0.000
0.004
RH,
B, T
77K
230K
300 K
RH,
B,T
Our results
JETP Letters 89, 707, (2009)
Comparison with Mn4Si7
U. Gottlieb at el., JMMM (2004)
J.H. Yao et al., Appl. Phys.Lett. 94, 072507 (2009)
Mn4Si7 Tc<50K MnxSi1-x TC> 300K
-3 -2 -1 0 1 2 3
-0.02
-0.01
0.00
0.01
0.02
RH,
B, T
56K
5K
Sample 1:T
g=300C
For sample grown at Tg =300 C coercive field Bc strongly rises (2.8 times) when temperature lowering from 56 K down to 5 K. It is so also for Ga1-x MnxAs (at Т ТС).
Contrary to that for sample grown at Tg =350 C coercive field Bc diminishes with temperature lowering from 59 K down to 5 K.
-3 -2 -1 0 1 2 3
-0.01
0.00
0.01
0.02
Sample 3:T
g = 350 C
RH,
B, T
5K
59K
Hall effect
Magnetization
Magnetic moment per Mn atom 0.1 B/Mn. In Mn4Si7 0.012 B/Mn.
B, T
Correlation between AHE and magnetization
Si1-хMnх/Al2O3 (№2) d=57 nm
-1 0 1
-2.0x10-7
0.0
2.0x10-7
-20
0
20
xya , O
hm*c
m
B, T
M, G
Coercitivity and saturation magnetization vs. temperature measured by AHE and SQUID
Magnetization. Temperature dependenceCurie temperature.
Coupling between local magnetic moments of MnD defects in the MnnSim host mediated by spin fluctuations (SF). For DMS M(T) could be fitted by
F(y) = 1 − yn, with y = T/TC ( n ≈ 2 for GaMnAs)
In the SF modey = T (T − Th
C)/Tc(TC − ThC)
ThC = 50 K – Curie temperature of
matrix (host). n = 1.3–1.5
Model
Mn atoms in molecular clusters ~ (3-5) %. Distance between them a0 ~ 10-12 Å. In the molecular cluster 4 - 5 Si atoms per Mn. Tetrahedral arrangement of Si surrounding Mn.
Si1-xMnX MnSiy
Mn4Si7 MnSi1.75
35%Mn MnSi1.86
HOSTWeak itinerant magnet of
helicoidal typeSpin density is delocolized due to hybridization of Mn 3d – states and Si (s,p) -
states
Magnetic defects, molecular cluster with magnetic moment (2-3) B/Mn Q. Liu et al. [Phys. Rev. B 77, 245211 (2008)]
Magnetic moment ~ 0.1 B/Mn
Model for long-range order FM
Two contributions RKKY (through free carriers 21022 cm-3)
The long-range ferromagnetic order at high temperatures is mainly due to the Stoner enhancement of the exchange coupling between magnetic defects through thermal spin fluctuations (“paramagnons”) in the matrix.Tugushev et al. Physica B (2006); Nikolaev et al. JETP letters (2009)
(Rij) – local susceptibility. SF(Rij)≈RKKY(ξSFkF)2 ≈N(EF)(ξSFkF)2
- ξSF – correlation length is about 1.5 nm, (kF)-1– 0.5 nm.
KTC 3020
Results for MnxSi1-x/Al2O3
The Hall resistance in MnxSi1-x is determined mainly by the anomalous component. Hysteresis is observed up to 230 К.
Magnetic moment is about 0.1B per Mn, that is tentimes higher than in Mn4Si7 0.01B /Mn.
At temperatures below 50 K resistivity decreasesdrastically.
Properties of our structures differ from Mn4Si7 .
Tc is about 300 K.
Comparison between MnxSi1-x on Al2O3 and GaAs
Comparison between MnxSi1-x on Al2O3 and GaAs
-0.8 -0.4 0.0 0.4 0.8-0.2
-0.1
0.0
0.1
0.2Mn
xSi
1-x/GaAs
N 4d=80nmT=300K
xy, 1
0-6*
cm
B, T
N 2d=57nm
N 5d=50nm
MnxSi
1-x/Al
2O
3
For MnxSi1-x/GaAs Hall resistance ρxy is remarkably higher then in MnxSi1-x/Al2O3
Comparison between MnxSi1-x/Al2O3 and MnxSi1-x/GaAs
samples
AHE in MnxSi1-x/GaAs is clearly observed at 300K and its amplitude weakly depends on temperature between 5 K and 190 K, while slope diminishes.
The Hall angle tangent = xy/ xx is ~ 10-2 (at 200 К), that corresponds to 20 Т for normal Hall effect if mobility 5 cm2/Vs .
-3 -2 -1 0 1 2 3-0.2
-0.1
0.0
0.1
0.2
-0.7 0.0 0.7-0.1
-0.0
0.0
0.0
N 5R
xx(5)/R
xx(290) = 0.63
T=186K
T=43K
xy, 1
0-6
cm
B, T
T=5K
T=283K
xy,1
0-6
cm
B, T
At saturation the magnetic moment per Mn atom is for
MnSi/Al2O3 ≈0.07 μB/Mn (200 K) ≈0.03 μB/Mn (300 K)
MnSi/GaAs≈0.3 μB/Mn (200 K)
≈0.08 μB/Mn (300 K)
Comparison between MnxSi1-x on Al2O3 and GaAs
Samples number/substrate
Rxx(77K)/Rxx(290K)
Growth temperature, Tg °C
d, nm Hc- coercitivity at 80
K (Oe)
AHEsign
Nо1Al2O3
0.94 300 40 2900-
Nо2Al2O3
0.93 300 57 2000-
Nо3Al2O3
0.85 350 55 4200-
№4GaAs
0.85 300 80 0 +
№5GaAs
0.84 300 50 0 +
№6GaAs
0.97 200 75 330+
№7GaAs
0.89 300 300 650-
Parameters of MnxSi1-x samples, x ≈ 0.35
Hole concentration p ≈ (2 – 3)1022 cm-3
ConclusionAHE is observed at room temperature being the main contribution to the Hall resistance. Hysteresis is observed up to 230 К.
Tc reaches more then 300 K.
Curie temperature and saturation magnetization is much higher than in Mn4Si7 and in previously studied Si based structures.
Properties of these films depend on substrate
We explain experimental results within the model of exchange through the spin fluctuations
Thank you for attention video-2011-03-25.3gp
PRB, 84, 075209 (2011)