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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)