A spin-valve-like magnetoresistance of an antiferromagnet- based tunnel junction Xavier Marti, Special thanks to : Josep Fontcuberta, Helena Reichlova, Pete Wadley, Joerg Wunderlich, Tomas Jungwirth Xavier Marti J. Zemen, V. Novak, B.G. Park, H. Reichlová, K. Olejnik, M. Cukr, O. Stelmakhovych, V. Holy, P. Nemec, P. Horodyska, E. Rozkotova, N. Tesarova, A. Shick, J. Masek, F. Maca, Y. Kurosaki, M. Yamada, H. Yamamoto, A. Nishide, J. Hayakawa, H. Takahashi, R. Campion, T. Foxon, B. Gallagher, P. Wadley, K. Edmonds, A. Rushforth, D. Petti, E. Albisetti, R. Bertacco, I.Fina, F. Sanchez, J. Fontcuberta, J. Wunderlich, T. Jungwirth MPI Halle14:30

Xavier Marti, Outline 1.Tunnel Anisotropic-Magnetoresistance. Strategy: large change in DOS(E F ) 2.Sample characterization: substrate/Py/IrMn/MgO/Pt layers 3.Spin-valve-like magnetoresistance IrMn/MgO/Pt 4.New strategy: large change of chemical potential at E F 5.I-II-V antiferromagnetic semiconductor: tetragonal LiMnAs/InAs 6.I-II-V antiferromagnetic semimetals: tetragonal CuMnAs/GaAs

FM insulator [AFM]

No-Mag FM insulator

Co Courtesy of Jan Zemen

Co Courtesy of Jan Zemen

No-Mag FM insulator

Park et al., PRL 100, (2008) Co: 0.1 %

Park et al., PRL 100, (2008) Co: 0.1 %

Park et al., PRL 100, (2008) CoPt: 10 % Co: 0.1 %

CoPtCo Courtesy of Jan Zemen

CoPtCo Courtesy of Jan Zemen

CoPtCo Courtesy of Jan Zemen

CoPtCo PtCo Park et al., PRL 100, (2008) CoPt: 10 % TAMR: Uniaxial anisotropy

CoPtCo PtCo Park et al., PRL 100, (2008) CoPt: 10 % TAMR: Uniaxial anisotropy M S-O M Schick et al., PRB 81, (2010)

18 spontaneous moment spin-orbit coupling Ta/Ru/Ta MnIr MgO Pt NiFe Antiferromagnetic Bimetallic alloy IrMn is already present in TMR structure Intention is to remove NiFe from the stack and place IrMn at the barrier Schick et al., PRB 81, (2010)

CoPt: 10 % Co: 0.1 % IrMn: ? %

Q: How to rotate AFM-coupled staggered moments?

W.H. Meiklejohn, J. Appl. Phys. 33 (1962) 1328

Q: How to rotate AFM-coupled staggered moments? D. Mauri, J. Appl. Phys. 62 (1987) 3047

W.H. Meiklejohn, J. Appl. Phys. 33 (1962) 1328 K. Takano, Phys. Rev. Lett. 79 (1997) 1130 D. Mauri, J. Appl. Phys. 62 (1987) 3047 M. Kiwi, EPL 48 (1999) 573 A.P. Malozemoff, Phys. Rev. B 35 (1987) 3679 P. Miltenyi, Phys. Rev. Lett. 84 (2000) 4224 N.C. Koon, Phys. Rev. Lett. 78 (1997) 4865 M. Kiwi, EPL 48 (1999) 573 F. Radu, J. Phys.: Condens. Matter 18, L29 (2006) Inspired by F. Radu PhD Thesis and Josep Nogues Talk (Prague 2012) (Not an exhaustive list)

Ta/Ru/Ta MnIr MgO Pt NiFe From conventional FM-FM to AFM-based tunnel junction Park et al., Nature Mater. 10, 347 (2011) US patent

Ta/Ru/Ta MnIr MgO Pt NiFe From conventional FM-FM to AFM-based tunnel junction Park et al., Nature Mater. 10, 347 (2011) US patent

Ta/Ru/Ta NiFe MnIr MgO Pt From conventional FM-FM to AFM-based tunnel junction Park et al., Nature Mater. 10, 347 (2011) US patent

Ta/Ru/Ta NiFe MnIr MgO Pt From conventional FM-FM to AFM-based tunnel junction DOS(2) AFM FM DOS(1) Park et al., Nature Mater. 10, 347 (2011) US patent

 Structural and magnetic characterization of the samples (

From X-ray diffraction studies we learn that: 1.IrMn is cubic (c/a = 1) [1] 2.IrMn is in “disordered” gamma-phase [2] 3.IrMn is in-plane not ordered [3] 4.IrMn is out-of-plane textured, (111) [1-3] 5.Ir content is close to 30% 6.Grains are ~10 nm 7.Magnetic structure is likely Q IrMn(111) QxQx QyQy Marti et al., PRL 2012

From X-ray diffraction studies we learn that: 1.IrMn is cubic (c/a = 1) [1] 2.IrMn is in “disordered” gamma-phase [2] 3.IrMn is in-plane not ordered [3] 4.IrMn is out-of-plane textured, (111) [1-3] 5.Ir content is close to 30% 6.Grains are ~10 nm 7.Magnetic structure is likely Q IrMn(111) QxQx QyQy Marti et al., PRL 2012

GS = 1/0.01 = 100 A ~ 10 nm Marti et al., PRL 2012

33 IrMn grain size ~ 10 nm Ru Ta Oxide Ta NiFe MgO IrMn

1 2 3 IrMn(111) QxQx QyQy From X-ray diffraction studies we learn that: 1.IrMn is cubic (c/a = 1) [1] 2.IrMn is in “disordered” gamma-phase [2] 3.IrMn is in-plane not ordered [3] 4.IrMn is out-of-plane textured, (111) [1-3] 5.Ir content is close to 30% 6.Grains are ~10 nm 7.Magnetic structure is likely Q3 Marti et al., PRL 2012

PHYSICAL REVIEW B 67, (2003) The magnetic structure is likely to be θ ≈ deg, so-called Q3 structure A C All spins contained in the (111) plane B Py Mn L 2,3 XMCD Net magnetic moment found in unpinned Mn DLS I06

PHYSICAL REVIEW B 67, (2003) The magnetic structure is likely to be θ ≈ deg, so-called Q3 structure A C All spins contained in the (111) plane B Py Net magnetic moment found in unpinned Mn Only at the FM/AFM interface DLS I06

SQUID magnetometer F. Radu, S-G model M-B model Marti et al., PRL 2012

Ta/Ru/Ta NiFe MnIr MgO Pt From conventional FM-FM to AFM-based tunnel junction DOS(2) AFM FM DOS(1) Park et al., Nature Mater. 10, 347 (2011) US patent ) TAMR SQUID Marti et al., PRL 2012

3 mT 50 mT B B Park et al., Nature Mater. 10, 347 (2011) US patent

Marti et al., PRL 2012 AFM TAMR : electrical reading of AFM moments 10K

Marti et al., PRL 2012 AFM TAMR : electrical reading of AFM moments 10K

42 AFM TAMR : irreversibility Park et al., Nature Mater. 10, 347 (2011) US patent CoPt: 10 % Co: 0.1 % IrMn: 100 %

AFM TAMR: control sample without the AFM Park et al., Nature Mater. 10, 347 (2011) US patent

AFM TAMR : either uniaxial (EB-induced) or unidirectional anisotropy? At very low temperatures signal is strongly unidirectional… H eb >>1

45 AFM TAMR : electrical reading of AFM moments R + ≠ R - R + = R - Marti et al., PRL 2012 Less TAMR = Less difference between initial and final states

46 Marti et al, AFM TAMR : electrical reading of AFM moments R + ≠ R - R + = R - Marti et al., PRL 2012 Less TAMR = Less difference between initial and final states

SQUID magnetometer Marti et al., PRL 2012 K AF (T  300K)  0 J EB (T  300K)  0 If K AF is low it is easier to rotate, but if J eb is also low, coupling is also low, and the AFM-rotation smaller

SQUID magnetometer Marti et al., PRL 2012 K AF (T  300K)  0 J EB (T  300K)  0 If K AF is low it is easier to rotate, but if J eb is also low, coupling is also low, and the AFM-rotation smaller B(T) 300 K: The two “metastable” states are separated less than K B T

Xavier Marti, Outline 1.Tunnel Anisotropic-Magnetoresistance. Strategy: large change in DOS(E F ) 2.Sample characterization: substrate/Py/IrMn/MgO/Pt layers 3.Spin-valve-like magnetoresistance IrMn/MgO/Pt 4.New strategy: large change of chemical potential at E F 5.I-II-V antiferromagnetic semiconductor: tetragonal LiMnAs/InAs 6.I-II-V antiferromagnetic semimetals: tetragonal CuMnAs/GaAs

Energy Density of states EFEF Tunnel transport  large change in DOS(EF) Charge control  large change in chemical potential

insulator Silicon transistor Energy EFEF Density of states

insulator Silicon transistor Energy EFEF Density of states

B ptp B 90 B0B0 I

Spin-dependent chemical potential shift in capacitively coupled gate instead of channel Ciccarelli, Zarbo, Irvine, Campion, Gallagher, Wunderlich, Jungwirth, Ferguson preprint ‘12

Common approach to spin-transistorInverted approach to spin-transistor

Doping Temperature Xavier Marti, GaAs (Ga,Mn)AsMnAs Ferromagnetic Semiconductor

III-VFM T C (K)AFM T N (K) FeN100 FeP115 FeAs77 FeSb GdN72 GdP15 GdAs19 GdSb27 II-VIFM T C (K)AFM T N (K) MnO122 MnS152 MnSe173 MnTe323 EuO67 EuS16 EuSe5 EuTe10 Xavier Marti, Intrinsic III-V and II-VI semiconductors Maca et al., JMMM 324, 1606 (2012)

Energy EFEF DOS

Crystal and magnetic structure: Bronger et al, Z. anorg. allg. Chem. 539, 175 (1986) THEORY Semiconductor with huge spin-orbit coupling Xavier Marti,

InAs 4.27A 4.28A THIN FILM EPILAYERS V. Novak, et al., J. Cryst. Growth 323, 348 (2011)

log(intensity) InAs 4.27A 4.28A THIN FILM EPILAYERS

LiMnAs has a bandgap InAs LiMnAs 4.27A 4.28A I. Wijnheijmer et al, Appl. Phys. Lett. In press dI/dV map

Is LiMnAs the only choice available? Xavier Marti, I

Xavier Marti, V. M. Ryzhkovsky, et al., Inorg. Mater (1995) A.E. Austin, et al., J. Appl. Phys (1962) TNTN RT CuMnAs, Mn 2 As prototype Courtesy of J. Zelezný

GaAs(004) GaAs(002) CuMnAs(001) CuMnAs(002) CuMnAs(003) CuMnAs(004) 6.30 Å (a) (b) (c) (d)

XRD Neutron d-spacing (Å)

67 Summary TAMR in FM metalsTAMR in AF bimetallic alloys Park et al., PRL 100, (2008)Schick et al., PRB 81, (2010) Spin-valve-like magnetoresistance of an antiferromagnetic-based tunnel junction Park et al., Nature Mater. 10, 347 (2011) US patent Electrical measurement of the AFM moments Marti et al, submitted 2011

Thanks for your attention !!! Xavier Marti, Special thanks to : Josep Fontcuberta, Helena Reichlova, Pete Wadley, Joerg Wunderlich, Tomas Jungwirth Xavier Marti V. Novak, B.G. Park, H. Reichlová, K. Olejnik, M. Cukr, O. Stelmakhovych, V. Holy, P. Nemec, P. Horodyska, E. Rozkotova, N. Tesarova, A. Shick, J. Masek, F. Maca, Y. Kurosaki, M. Yamada, H. Yamamoto, A. Nishide, J. Hayakawa, H. Takahashi, R. Campion, T. Foxon, B. Gallagher, P. Wadley, K. Edmonds, A. Rushforth, D. Petti, E. Albisetti, R. Bertacco, I.Fina, F. Sanchez, J. Fontcuberta, J. Wunderlich, T. Jungwirth MPI Halle14:30