Interface induced perpendicular magnetic anisotropy and giant tunnel magnetoresistance in Co 2 FeAl Heusler alloy based heterostructures

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Erik Porter
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Heusler Alloys for Spintronic Devices organized by The Center for Spintronic Materials, Interfaces, and Novel

magnetoresistance in Co 2 FeAl Heusler alloy based heterostructures Perpendicular MTJ Co 2 FeAl: B2 structure Co Fe 2

Barrier Free Hiroaki Sukegawa National Institute for Materials Science (NIMS), Tsukuba, Japan In collaboration with

1 Heusler Alloys for Spintronic Devices organized by The Center for Spintronic Materials, Interfaces, and Novel Architectures (C SPIN) Friday, July 31, 2015 Interface induced perpendicular magnetic anisotropy and giant tunnel magnetoresistance in Co 2 FeAl Heusler alloy based heterostructures Perpendicular MTJ Co 2 FeAl: B2 structure Co Fe 2 (FeAl) Ref. Barrier Free Hiroaki Sukegawa National Institute for Materials Science (NIMS), Tsukuba, Japan In collaboration with Magnetic Materials Unit members in NIMS: S. Mitani, K. Inomata, Z. C. Wen (~ now Tohoku Univ. Japan), T. Scheike, T. Furubayashi, J. P. Hadorn, T. Ohkuboand K. Hono Al Co University of Minnesota, Minneapolis, Minnesota, USA, July 30 31, 2015

2 NIMS: National Institute for Materials Science, Tsukuba, Japan (permanent staffs: 410, total ~1,500) Spintronics group members Magnetic Materials Unit GL Leader 2 Director KEK, AIST, Univ. Tsukuba, NIMS Tsukuba Magnetic Materials Group Spintronics Group Nanostructure Analysis Group Admin. Tokyo Equipment Thin film deposition systems Sputtering E beam lithography Microfab. facility Electric measurement Prober MBE CIPT (TMR measurement) Sputtering MBE cluster Patterned sample

3 3 1. Background Co 2 FeAl Heusler alloy based magnetic tunnel junctions (MTJs) for MRAM applications 2. Perpendicular anisotropy in Co 2 FeAl ultra thin films 2.1 Perpendicular magnetic anisotropy (PMA) and TMR in ultrathin Co 2 FeAl/MgO structures 2.2 Enhanced PMA by Ru(022 3) underlayer 2.3 Possible mechanism of PMA 3. Co 2 FeAl MTJs with a lattice matched MgAl 2 O 4 coherent barrier

Amp Output High density MTJ (magnetic tunnel junction) (in plane mag.

4 4 C. Chappert, A. Fert and F. N. V. Dau, Nat. Mater. 6, 813 (2007) Bit lines WL I R BL MTJ R AP : 1 R P : 0 Nonvolatile Infinite endurance High speed Word lines MTJ FETs (to R Ref ) W Op Amp Output High density MTJ (magnetic tunnel junction) (in plane mag. type) Parallel (P) Antiparallel (AP) FM (free layer) Tunneling barrier TMR (tunnel magnetororesistance) TMR ratio = R R AP R R P AP P FM (pinned layer) P TMR Antiferromagnet FM: Ferromagnet Low resistance R P High resistance R AP High TMR Field High output (high speed reading)

5 (1) High signal output (TMR) with tunable device resistance High spin polarization materials Co based

stability of stored information High perpendicular magnetic anisotropy (PMA) Bulk induced anisotropy

writing energy (low current density for STT writing) Low magnetic damping materials Co based Heusler alloys

5 5 (1) High signal output (TMR) with tunable device resistance High spin polarization materials Co based Heusler alloys New (coherent) tunneling barrier materials MgAl 2 O 4 based barrier (2) High thermal stability of stored information High perpendicular magnetic anisotropy (PMA) Bulk induced anisotropy Multilayers, L1 0 /D0 22 based alloys Interface induced anisotropy ultrathin FM/insulator interface (3) Low writing energy (low current density for STT writing) Low magnetic damping materials Co based Heusler alloys Mn based PMA alloys (4) New writing technology Magnetic anisotropy control by electric field Spin orbit torque Interface PMA system

6 L2 1 X 2 YZ Disordered structures B2: X (Y, Z) A2: (X, Y, Z) bcc structure Z X Y Site disordering Magnetic moment per unit cell (m B ) Co 2 FeSi After I. Galanakis, PRB 66, 174429 (2002) S.

6 6 L2 1 X 2 YZ Disordered structures B2: X (Y, Z) A2: (X, Y, Z) bcc structure Z X Y Site disordering Magnetic moment per unit cell (m B ) Co 2 FeSi After I. Galanakis, PRB 66, (2002) S. Wumehl et al (PRB, 2005) 7 Co 6 2 CrAl Co 2 MnSi Co 2 MnAs Fe 2 MnSi Co 2 MnGe Co 2 MnSb Ru 2 MnSi Co 2 MnSn Co 2 FeSi 1000 Ru 2 MnGe Rh 2 MnIn Co 2 FeAl 4 Ru 2 MnSn Rh 2 MnTi Ni 2 MnAl Slater Pauling rule M t = Z v 24 Half metallic material Co 2 VAl Fe 2 MnAl Mn 2 VAl Co 2 TiAl Fe 2 VAl Mn 2 VGe Co 2 TiSn Fe 2 CrAl Co 2 MnAl Co 2 MnGa Rh 2 MnAl Rh 2 MnGa Ru 2 MnSb Rh 2 MnGe Rh 2 MnSn Rh 2 MnPb Valence electron number per unit cell (Z t ) Curie temperature (K) Lower P Band structure of half metals Co based Heusler alloy: Co 2 YZ High Curie temperatures High spin polarization Low magnetic damping even in B2 structure E F Gap P = 1 TMR: infinite

7 L2 1 (X 2 YZ) Co Fe Al B2 (disordering Fe Al) Fe 1. Small lattice misfit of CFA/MgO(001) Misfit: ~3.

, PRB81, 140402(R) (2010). AMR Y. Sakuraba et al., APL104, 172407 (2014).

band structure High quality CFA/MgO MTJs can be fabricated using a sputtering method. 2.

, PRB82, 092402 (2010). 3. Possible low damping constant (in plane mag.

7 7 L2 1 (X 2 YZ) Co Fe Al B2 (disordering Fe Al) Fe 1. Small lattice misfit of CFA/MgO(001) Misfit: ~3.8% Co B2 ordered CFA is generally obtained by sputtering deposition. Band calculation W. H. Wang et al., PRB81, (R) (2010). AMR Y. Sakuraba et al., APL104, (2014). Al Not a perfect half metal, but fully spin polarized 1 band Negative AMR in B2 CFA film: a nearly halfmetallic band structure High quality CFA/MgO MTJs can be fabricated using a sputtering method. 2. Large TMR in CFA/MgO MTJs Epitaxial CFA/MgO/CoFe(0.5 nm)/cfa TMR: 785% (10 K), 360% (RT) W. H. Wang, HS et al., PRB82, (2010). 3. Possible low damping constant (in plane mag.) High spin polarization and coherent tunneling Less temperature dependence of TMR ratio ~ for 50 nm thick CFA(001) S. Mizukami et al., JAP105, 07D306 (2009). (Tohoku group) Effective for spin transfer torque (STT) switching

8 8 1. Background Co 2 FeAl Heusler alloy based magnetic tunnel junctions (MTJs) for MRAM applications 2. Perpendicular anisotropy in Co 2 FeAl ultra thin films 2.1 Perpendicular magnetic anisotropy (PMA) and TMR in ultrathin Co 2 FeAl/MgO structures 2.2 Enhanced PMA by Ru(022 3) underlayer 2.3 Possible PMA mechanism 3. Co 2 FeAl MTJs with a lattice matched MgAl 2 O 4 coherent barrier

9 9 Perpendicular magnetic anisotropy (PMA) PMA: higher thermal stability, lower STT switching current density Bulk induced PMA: b PMA Bulk PMA materials, Multilayers L1 0 FePt, D0 22 MnGa, amorphous TbFeCo, (Co/Pt) n, (Co/Pd) n Fe Small uniaxial magnetocrystalline anisotropy can be expected in bulk of cubic Heusler alloys. Use of Interface effect Al Co Interface induced PMA: i PMA Interface at ultrathin layer and oxide Pt/Co/AlOx trilayers B. Rodmacq et al., PRB 79, (2009). CoFeB(1)/MgO(0.9)/CoFeB(1.3 nm) p MTJ S. Ikeda et al., Nat. Mater. 9, 721 (2010). TMR ratio = 120% K u = erg/cm 3 J c0 = 3.6 MA/cm 2 Ultra thin Co 2 FeAl (CFA)/MgO structure 0 H (T)

10 M H curves t = 0.8 nm: perpendicular MgO(001) sub.

6 nm: in plane T ex = 350 C T ex = 350 C Sputter deposition

annealing T ex Pt cap MgO (2.0 nm) Co 2 FeAl (0.

Co 2 FeAl/MgO interface K u = 2 10 6 erg/cm 3 ( 10 5 J/m 3 )

10 10 M H curves t = 0.8 nm: perpendicular MgO(001) sub./cr/cfa(t nm)/mgo/pt t = 1.6 nm: in plane T ex = 350 C T ex = 350 C Sputter deposition Area enclosed by the curves: PMA energy density (K u ) Post annealing T ex Pt cap MgO (2.0 nm) Co 2 FeAl (0.8 nm) Cr (40 nm) MgO(001) Sub. Wen et al., APL98, (2011). Co 2 FeAl/MgO interface K u = erg/cm 3 ( 10 5 J/m 3 ) epitaxial (001) growth Cf. CoFeB/MgO: 2~ erg/cm 3 ( 10 5 J/m 3 ) *M. Yamanouchi et al., J. Appl. Phys. 109, 07C712 (2011).

11 11 T ex = 300 C MgO(001) sub./cr/cfa(t nm)/mgo/pt Saturation magnetization M s K u t vs. t PMA PMA: t < 1.1 nm IMA t > 0.8 nm: M s > 1000 emu/cm 3 Pt cap MgO (2.0 nm) Co 2 FeAl (t nm) Cr (40 nm) MgO(001) Sub. Post annealing T ex Z. C. Wen et al., APL98, (2011). Shape anisotropy K u t = (K V 2πM S2 )t + K s slope intercept Bulk PMA energy density K V K v = erg/cm 3 ( 10 5 J/m 3 ) Interfacial PMA energy density K s K s = 1.04 erg/cm 2 (mj/m 2 ) CFA/MgO interface induces PMA In plane (mainly lattice distortion) Perpendicular

12 12 Wen et al., APEX5, (2012). MTJs: Cr/CFA(1.0 nm)/mgo/fe/co 20 Fe 60 B 20 improvement of the interface structure TMR curve Area: 10x5 m 2 H Fe(0.1) Ta cap Co 20 Fe 60 B 20 (1.3) MgO(1.8) Mg(0.1) Unit: nm CFA(1.0) Cr (40) T ex = 325 C RT CFA CoFeB AP P MgO(001) Sub. perp TMR at RT = 53% ~ 91% Ultra thin CFA (~1 nm) still has a high effective spin polarization.

13 13 1. Background Co 2 FeAl Heusler alloy based magnetic tunnel junctions (MTJs) for MRAM applications 2. Perpendicular anisotropy in Co 2 FeAl ultra thin films 2.1 Perpendicular magnetic anisotropy (PMA) and TMR in ultrathin Co 2 FeAl/MgO structures 2.2 Enhanced PMA by Ru(022 3) underlayer 2.3 Possible PMA mechanism 3. Co 2 FeAl MTJs with a lattice matched MgAl 2 O 4 coherent barrier

14 14 Cr(40)/CFA(1.0)/MgO(2 nm) Out of plane( ) t CFA = 1 nm Z. C. Wen et al., Adv. Mater. 26, 6483 (2014). Ru(40)/CFA(1.0)/MgO(1.8 nm) Out of plane( ) T ex = 350 C In plane ( ) In plane ( ) H k ~7 koe M s ~ 1100 emu/cm 3 K u Cr buffer: erg/cm 3 ( 10 5 J/m 3 ) T ex = 350 C B2 (or A2 (bcc)) (001) bcc(001) Pt cap MgO (2.0 nm) Co 2 FeAl (1 nm) Cr (40 nm) MgO(001) Sub. 4 times K u Ru buffer: erg/cm 3 ( 10 5 J/m 3 ) T ex = 350 C? hcp? Ta Cap MgO (1.8 nm) Co 2 FeAl (1 nm) Ru (40) MgO(001) Sub. Enhancement of PMA using the Ru buffer K s (Cr buffered) = 1.0 erg/cm 2 K s (Ru buffered) = 2.2 erg/cm 2

15 15 Out of plane (2 scan) Pole scan for Ru Co 2 FeAl (20 nm) Ru (40 nm) MgO(001) Sub. Ru: Only (022 3), CFA: only (00L) Intensity (Linear scale) Ru (-2, 1, 1, 0) (deg.) 4 fold peaks for Ru: mixture of variants Epitaxial growth of 4 fold symmetry Ru(022 3) on MgO(001) Pole scan for CFA Intensity Epitaxial growth of B2 ordered CFA(001) on Ru(022 3)

$4278 nm a axis c axis (03 34) (02 23) (01 12) Nano electron beam diffraction 0 1 000 0 11 02 3 0002 01 1 01 (0001)$

16 16 Amo? rock salt (001) bcc (001) hcp (022 3) Ru (40)/CFA (1.2)/MgO (1.8)/[Fe (0.1)/CoFeB (1.3 nm)] observation: MgO{110} plane normal (0001) Model (Bulk hcp Ru) a Ru = nm c Ru = nm a axis c axis (03 34) (02 23) (01 12) Nano electron beam diffraction (0001) (02 23): (02 23) (03 34): 3.26 (02 23) (01 12): 8.20 Nearly Ru(022 3) growth (To be more accurate, (033 5) growth) 0 2 Why do CFA and MgO grow epitaxially on it?

17 17 Plan view for Ru(022 3) MgO [110] MgO[100] Side view Epitaxial relationship: MgO(001)/Ru(022 3)/CFA(001) ~11% (MgO/Ru) Lattice mismatch ~8% (Ru/CFA) cf. ~5% (MgO/Cr), ~1% (Cr/CFA) Nearly square lattice structure of the Ru plane can act as a template of the CFA(001) growth

18 18 Cr/CFA/Cr Ru/CFA/Ru 2K s (Cr/CFA) Cr CFA Cr 2K s (Ru/CFA) Ru CFA Ru Subtraction of dead layer thickness: t d Both Cr/CFA and Ru/CFA interfaces show negligible contribution to interface PMA K s (Cr or Ru/CFA) ~ 0.1 erg/cm 2 cf. CFA/MgO interface: K s = 1.0 erg/cm 2 (Cr buffer), 2.2 erg/cm 2 (Ru buffer) Possible origin of the enhanced PMA: Improvement of CFA/MgO lattice combination due to a weaker effect from the Ru lattice MgO CFA Ru Weaker bonding? MgO cf. Cr buffer: CFA lattice with a structure of Cr/CFA/MgO is dominated by the Cr(001) lattice owing to the very small lattice mismatch = not a perfect CFA/MgO interface (related to lattice distortion) Stronger bonding? CFA Cr

19 19 Z. C. Wen et al., Adv. Mater. 26, 6483 (2014). Ru/CFA (1.2)/MgO (1.8)/Fe (0.1)/Co 20 Fe 60 B 20 (1.3 nm) p MTJ T ex = 325 C RT 10 K Ta/Ru cap Co 20 Fe 60 B 20 (1.3 nm) Fe (0.1 nm) MgO (1.8 nm) Co 2 FeAl (1.2 nm) Ru (40 nm) MgO(001) Sub. TMR: 132% at RT (237% at 10 K) (Cr buffer: 91% at RT) Over 130% TMR at RT in p MTJ using the interface PMA of Co 2 FeAl/MgO The epitaxial Ru with a high crystal index opens up a new path in the development of engineered heterostructures combining hcp and cubic or tetragonal materials.

20 20 1. Background Co 2 FeAl Heusler alloy based magnetic tunnel junctions (MTJs) for MRAM applications 2. Perpendicular anisotropy in Co 2 FeAl ultra thin films 2.1 Perpendicular magnetic anisotropy (PMA) and TMR in ultrathin Co 2 FeAl/MgO structures 2.2 Enhanced PMA by Ru(022 3) underlayer 2.3 Possible PMA mechanism 3. Co 2 FeAl MTJs with a lattice matched MgAl 2 O 4 coherent barrier

21 K. Nakamura et al., PRB 81, 220409(R) (2010). Hybridization between oxygen and Fe atoms shifts up m = 0 (3d z2 ) above E F O Mg [001] H. X. Yang et al., PRB 84, 054401 (2011).

21 21 K. Nakamura et al., PRB 81, (R) (2010). Hybridization between oxygen and Fe atoms shifts up m = 0 (3d z2 ) above E F O Mg [001] H. X. Yang et al., PRB 84, (2011). O Mg Fe [100] Fe M s O: 2p z Fe: 3d z 2 (m = 0) Fe Co unoccupied Hybridization between oxygen 2p z and Fe 3d z2 orbitals plays an important role for PMA in the Fe/MgO system The calculated PMA energy density of Fe/MgO is much larger than that of Co/MgO

22 Co 2 FeAl = Co rich (50 at.%) alloy However, the band structures of Co based Heusler alloys are considerably different from those of Fe or Co owing to their half metallic properties. 22 Bruno model: spin orbit interaction is treated as a perturbation for the tight binding approximation Anisotropy of orbital magnetic moments between perpendicular (m orb ) and in plane directions (m orb )is proportional to PMA (for 3d transition metals). Angular dependent x ray magnetic circular dichroism (XMCD) study To deduce the orbital magnetic moments along perpendicular and in plane directions Element specific PMA energy Spin orbit splitting (33 mev for Fe) MgO (2 nm) CFA (t) Cr (40 nm) MgO(001)

23 23 In collaboration with Prof. Okabayashi (Univ. Tokyo) BL 7A in Photon Factory, KEK MgO (2 nm) CFA (t) Cr (40 nm) MgO(001) J. Okabayashi, HS et al., APL103, (2013). MgO(001)sub./Cr(40 nm)/cfa(t)/mgo(2nm) Spectra taken in normal incidence (NI) and grazing incidence (GI) revealed the anisotropic orbital moments. PMA in plane anisotropy Fe L 2,3 edges Co L 2,3 edges XMCD intensity XMCD intensity anisotropic orbital moments Large anisotropic Fe orbital moments at the CFA/MgO interface (m orb (Fe) > m orb (Fe)) Bruno model: 0.37 erg/cm 2 (mj/m 2 ) XMCD result suggests contribution of Fe atoms (negligible small for Co) in CFA

24 24 Ab initio calculation by Prof. Shirai Group (Tohoku U) D. Mori et al., EB 07, Intermag 2012 PMA arises from Co terminated interface for CFA/MgO(001) system (MgO/L2 1 CFA/MgO) K s : Interfacial PMA enargy density Co terminated case K s Co = 0.99 erg/cm 2 (mj/m 2 ) PMA FeAl terminated case K s FeAl = 0.49 erg/cm 2 In plane MA Relevant report R. Vadapoo, A. Hallal, M. Chshiev (SPINTEC group) arxiv: v1 Co terminated case K s Co ~ 1.3 erg/cm 2 (mj/m 2 ) PMA 11 ML of Heusler MgO Co terminated CFA MgO K s (exp. Cr buffered) = 1.0 erg/cm 2 K s (exp. Ru buffered) = 2.2 erg/cm 2 PMA [001] PMA is theoretically expected only in Co terminated CFA, however FeAl terminated CFA is more thermodynamically stable Atomic model of B2 Co 2 FeAl(001) Al Fe Co (Fe Al) Co (Fe Al) atomic plane Co atomic plane Termination layer of CFA? Determination of the interfacial structure is needed

25 25 (at.%) Cr Fe Co Co: 2.50 nm Co,Fe EDS: energy dispersive X ray spectroscopy Elemental Profile Gaussian Fit Fe: 2.61 nm Al: 3.68 nm O: 4.02 nm Al Mg: 4.35 nm O Mg Ru Al diffusion TEM sample T ex = 350 C Ru cap MgO (1.8 nm) Co 2 FeAl (1.2 nm) Cr (40 nm) MgO(001) Sub. Wen et al., unpublished. Out of plane( ) T ex = 350 C In plane ( ) Distance (nm) Significant Al diffusion from CFA into MgO The CFA layer is no longer a Heusler alloy Solid phase reaction at the CFA/MgO interface Co 2 FeAl MgO barrier Co Fe (+Cr, Al) Mg Al O Cr CFA MgO Ru cap Enhancement of hybridization between Fe and O orbitals? (under investigation) Importance of sub nm scale structural analyses

26 1. Background Co 2 FeAl Heusler alloy based magnetic tunnel junctions (MTJs) for MRAM applications 2. Perpendicular anisotropy in Co 2 FeAl ultra thin films 2.

26 26 1. Background Co 2 FeAl Heusler alloy based magnetic tunnel junctions (MTJs) for MRAM applications 2. Perpendicular anisotropy in Co 2 FeAl ultra thin films 2.1 Perpendicular magnetic anisotropy (PMA) and TMR in ultrathin Co 2 FeAl/MgO structures 2.2 Enhanced PMA by Ru(022 3) underlayer 3. Co 2 FeAl MTJs with a lattice matched MgAl 2 O 4 coherent barrier (In plane magnetized MTJ)

27 27 New coherent barrier material: Spinel MgAl 2 O 4 Giant RT tunnel magnetoresistance (TMR) Non deliquescence Tunable lattice parameter: Good lattice matching with 3d ferromagnetic electrodes R. Shan, HS et al., Phys. Rev. Lett. 102, (2009) H. Sukegawa et al. Appl. Phys. Lett 96, (2010), Phys. Rev. B 86, (2012) O gemstone Al CoFe ~0.809 nm Mg MgAl 2 O 4 CoFe {220} spots: Spinel structure (004) (044) (0 22) (022) Fe MgAl 2 O 4 Fe Fe[001] Fe[110] (040) (0 2 2) (02 2) Almost perfect lattice matching 2 nm Max TMR ratio : 328 % (RT) : 494 % (4 K) Giant TMR owing to coherent tunneling effect in non MgO barrier 1 transport mechanism is still valid!

Current status of spinel based MTJs Mg Al film Post oxidation Crystalline Mg Al O(001) Perfect lattice matching with 3d FM/Co based Heuser alloys Large TMR: >300% Phys. Rev.

105, 092403 (2014). 28 Electrode materials bcc Fe (a =0.2866 nm) L2 1 Co 2 FeSi (a = 0.564 nm) L1 0 FePt (a = 0.385 nm) DO 22 MnGa (a = 0.

4 Next generation spintronics materials TMR at room 室温 TMR temperature 比 [%] (%) 600 500 400 300 200 100 0 TMR at RT (CoFe(B) electrodes) Amorphous アルミナバリア AlO x barrier MgO barrier バリア MgAl

28 Current status of spinel based MTJs Mg Al film Post oxidation Crystalline Mg Al O(001) Perfect lattice matching with 3d FM/Co based Heuser alloys Large TMR: >300% Phys. Rev. B 86, (2012). Wide RA range: m 2 (STT switching) Interface induced PMA Status Solidi RRL 8, 841 (2014). Fe Fe Phys. Rev. Lett. 102, (2009). Appl. Phys. Lett. 103, (2013); ibid.105, (2014). 28 Electrode materials bcc Fe (a = nm) L2 1 Co 2 FeSi (a = nm) L1 0 FePt (a = nm) DO 22 MnGa (a = nm) Lattice mismatch Mismatch (%) for (001) growth vs. MgO vs. MgAl 2 O 4 based (0.421 nm) ( nm) Next generation spintronics materials TMR at room 室温 TMR temperature 比 [%] (%) TMR at RT (CoFe(B) electrodes) Amorphous アルミナバリア AlO x barrier MgO barrier バリア MgAl スピネルバリア 2 O 4 barrier (Fe electrode) (Fe 電極 ) MgAl スピネルバリア 2 O 4 barrier (CoFe (CoFe electrode) 電極 ) Tohoku Anelva&AIST 西暦 [ 年 ] Tohoku Tohoku AIST IBM NIMS INESC Nancy Tohoku AIST Tohoku MIT IBM NVE CAS CNRS THALES Year MgAl 2 O 4

29 29 T. Scheike et al., APL105, (2014). In plane magnetized MTJ IrMn (12 nm) CoFe (5 nm) Mg Al O Co 2 FeAl (5 nm) TMR ratio (%) TMR: 236% RA: 1.8 k m 2 a MgAl2O4 /2 2 ~ nm Magnetic field (Oe) Cation disorder spinel Mg, Al HAADF STEM bcc CoFe MgOsub[001] MgOsub[100] Mg Al O t MAO = nm B2 CFA 2nm CFA(440)&CoFe(220) Filter Mg Al O The indices for a spinel lattice Cation disorder spinel structure CFA a L21 /2 ~ nm O B2 Co 2 FeAl Co Fe Al (random occupation) Misfit: ~0% (cf. MgO/CFA ~3.8%) Perfect lattice matching Giant TMR effect in CFA/Mg Al O/CoFe MTJs B2 CFA % TMR at room temperature Latest data > 340%

30 30 Co 2 FeAl based heterostructures Interface induced PMA (1) Perpendicular magnetic anisotropy in a Cr/Co 2 FeAl/MgO (K s ~ 1 erg/cm 2 ) and p TMR of 91% at RT. (2) Ru buffer layer as a new ferromagnetic layer growth: Unusual crystallographic orientation Ru(02 23) buffer enhanced PMA (K s ~ 2.2 erg/cm 2 ) and p TMR (132% at RT) (3) Al interdiffuction from CFA layer to barrier was confirmed; the Fe O hybridization owing to the interfacial reaction could be responsible for the strong PMA. Buffer orientation K u (Merg/cm 3 ) for 1 nm Cr buffer bcc (001) Ru buffer hcp ~(022 3) K s (erg/cm 2 ) TMR (%) 91 (RT) 132 (RT) Review of PMA in CFA based heterostructures Sukegawa et al., SPIN 4, (2014). Lattice matched MTJ using Spinel barrier Lattice matched CFA/MgAl 2 O 4 /CoFe MTJs were successfully developed and giant TMR more than 280% at RT was demonstrated. CFA based (or CFA derived) heterostructures will be a promising candidate for future spintronics applications

New perpendicular magnetization material: N deficient MnGaN MnGa N

(100) Reactive sputtering D0 22 Mn 3 Ga (tetragonal L2 1 ) Ga Mn N

antiferromagnet) Mn 57 Ga 32 N 11 (N deficient, but structurally

50nm Antiperovskite (E2 1 ) single phase PMA film 300 K E2 1 MnGaN:

2 MJ/m 3 ) Flat film structure Low saturation magnetization (~100

31 New perpendicular magnetization material: N deficient MnGaN MnGa N (50nm) MgO sub.(100) Reactive sputtering D0 22 Mn 3 Ga (tetragonal L2 1 ) Ga Mn N introduction Anti perovskite Mn 3 GaN N Mn Ga 31 (bulk Mn 3 GaN: antiferromagnet) Mn 57 Ga 32 N 11 (N deficient, but structurally homogeneous) XRD M H loops Cross sectional TEM D0 22 MnGa: very rough 50nm Antiperovskite (E2 1 ) single phase PMA film 300 K E2 1 MnGaN: atomically flat 50nm Ferromagnetic MnGaN with PMA (K u ~ 0.2 MJ/m 3 ) Flat film structure Low saturation magnetization (~100 emu/cc) Curie temperature >> room temperature Relatively high spin polarization ~ 57% (PCAR) New PMA material for spintronics Lee et al., APL107, (2015).

Perpendicular Magnetic Multilayers for Advanced Memory Application

Perpendicular Magnetic Multilayers for Advanced Memory Application Sangmun Oh; Zheng Gao Kochan Ju; Lijie Guan HGST Wafer Development Team 2012 HGST, a Western Digital company 2012 HGST, a Western Digital