1. Magnetic and transport properties of SiMn films with the high Mn content
Aronzon B.A.
PRB, 84, (2011)
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
Moscow State University, Russia
Dipartamento di Fisica, Universita di Roma
NIFTI, N. Novgorod , Russia
Lappeenranta University of Technology, Finland

2. Outline
1 Introduction.
What is known about SiMn structures?
2 Transport, AHE
3 Magnetic properties
4 Model
5 Conclusion

3. MnxSi1-x
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 acceptors
Binary compounds of 3d metals with Si are weak itinerant
magnets of helicoidal type with Curie temperature <50K
(no hysteresis loop). Si Mn

4. What is known about magnetic properties of MnxSi1-x
1. Ion beam implantation Mn (х ≈ 0.8 %) : Tc > 400 K (M. Bolduc et al., Phys. Rev. B 71, (2005)).
Magnetism is due to paramagnetic defects T. Dubroca et al., Appl. Phys. Lett. 88,
(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, (2006); 102, (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, (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, (2009)).
5. Mn –Si complexes (2-3) B/Mn (Q. Liu et al. Phys. Rev. B 77, (2008)) and self- organized in Si1-xMnx molecular clusters (S. Zhou et al. PRB 75, (2007); 80, (2009)) (> 0.2 B/Mn)
Mn4Si7 ТС ≈ 50К (A. Sulpice et al., JMMM , 519 (2004)).

5. Method: Anomalous Hall Effect
The Hall resistance RHd= yx = R0B + RsM
R0 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 impurity
cross-section seen by beam of electrons
possesses 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

6. 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

7. Parameters of MnxSi1-x samples, x ≈ 0.35
Samples number/
substrate
Rxx(77K)/
Rxx(290K)
Growth temperature, Tg °C
d, nm
Hc- coercitivity at 80 K (Oe)
AHE
sign
Nо1
Al2O3
0.94
300 40
2900 -
Nо2
0.93 57
2000
Nо3
0.85
350 55
4200 №4
GaAs 80 + №5
0.84 50 №6
0.97
200 75
330 №7
0.89
650
Hole concentration p ≈ (2 – 3)1022 cm-3

8. Microanalysis Report
EDAX ZAF Quantification Standardless SEC Table : Default

9. Anomalous Hall effect up to room temperature
Hall resistance
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  21022 cm-3.
Rs  2.410-8 Ohmcm/Gs (10-7 Ohmcm/Gs for GaMnAs with p  1021 cm-3,
S.H. Chun, et al., Phys. Rev. Lett. 98, (2007) ).

10. Comparison with Mn4Si7
U. Gottlieb at el., JMMM (2004) and
Our results

11. Comparison with (Si:H)Mn
Our results
J.H. Yao et al., Appl. Phys.Lett. 94, (2009)
JETP Letters 89, 707, (2009)
Comparison with Mn4Si7
MnxSi1-x TC> 300K
Mn4Si7 Tc<50K
U. Gottlieb at el., JMMM (2004)

12. Hall effect
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.

13. Magnetic moment per Mn atom  0.1 B/Mn.
Magnetization
B, T
Magnetic moment per Mn atom  0.1 B/Mn.
In Mn4Si7  B/Mn.

14. Correlation between AHE and magnetization
Si1-хMnх/Al2O3
(№2) d=57 nm

15. Coercitivity and saturation magnetization
vs. temperature measured by AHE and SQUID

16. Magnetization. Temperature dependence
Curie temperature.
Magnetization. Temperature dependence
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 mode
y = T (T − ThC)/Tc(TC − ThC)
ThC = 50 K – Curie temperature of matrix (host).
n = 1.3–1.5

17. Weak itinerant magnet of
Model
Si1-xMnX MnSiy
Mn4Si MnSi1.75
35%Mn MnSi1.86
Magnetic defects, molecular cluster with magnetic moment (2-3) B/Mn
Q. Liu et al. [Phys. Rev. B 77, (2008)]
HOST
Weak itinerant magnet of
helicoidal type
Spin density is delocolized due to hybridization of Mn 3d – states and Si (s,p) - states
Magnetic moment ~ 0.1 B/Mn
Mn atoms in molecular clusters ~ (3-5) %. Distance between them a0 ~ Å. In the molecular cluster Si atoms per Mn. Tetrahedral arrangement of Si surrounding Mn.

18. Model for long-range order FM
Two contributions
RKKY (through free carriers 21022 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.

19. 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 0.1B per Mn, that is ten
times higher than in Mn4Si7 0.01B /Mn.
At temperatures below 50 K resistivity decreases
drastically.
Properties of our structures differ from Mn4Si7 .
Tc is about 300 K.

20. Comparison between MnxSi1-x on Al2O3 and GaAs

21. Comparison between MnxSi1-x on Al2O3 and GaAs

22. Comparison between MnxSi1-x/Al2O3 and MnxSi1-x/GaAs samples
For MnxSi1-x/GaAs Hall resistance ρxy is remarkably higher then in MnxSi1-x/Al2O3
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 ~ (at 200 К), that corresponds to  20 Т for normal Hall effect if mobility 5 cm2/Vs .

23. Comparison between MnxSi1-x on Al2O3 and GaAs
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)

24. Parameters of MnxSi1-x samples, x ≈ 0.35
Samples number/
substrate
Rxx(77K)/
Rxx(290K)
Growth temperature, Tg °C
d, nm
Hc- coercitivity at 80 K (Oe)
AHE
sign
Nо1
Al2O3
0.94
300 40
2900 -
Nо2
0.93 57
2000
Nо3
0.85
350 55
4200 №4
GaAs 80 + №5
0.84 50 №6
0.97
200 75
330 №7
0.89
650
Hole concentration p ≈ (2 – 3)1022 cm-3

25. Thank you for attention
Conclusion
AHE 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
PRB, 84, (2011)
Thank you for attention