SPring-8/SACLA ฼⏝◊✲ᡂᯝ㞟

Section B%                             %/;8X ⥺☢Ẽ෇஧Ⰽᛶ࡟ࡼࡿ Pt/Y3Fe5O12 ࡢ☢ᛶゎᯒMagnetic Analysis for Pt/Y3Fe5O12 Probed by X-ray Magnetic CircularDichroism㔝ᓮ ὒ a, Ἑ㔝 Ḡ b, ཎ⏣ 㞞ྐ a, ᒣཱྀ ⪽ a, ຍ⸨ ᫭ᙪ a, ᇽ๓ ࿴ᙪ a
Hiroshi Nozakia, Yasushi Kounob, Masashi Haradaa, Satoshi Yamaguchia,Akihiko Katoa, Kazuhiko Dohmaeaa(ᰴ)㇏⏣୰ኸ◊✲ᡤ, b(ᰴ)ࢹࣥࢯ࣮
 Toyota Central Research & Development Labs., Inc., bDENSO Co., Ltd.
aX ⥺☢Ẽ෇஧Ⰽᛶ ᐃ࡟ࡼࡾࠊPt/Y3Fe5O12(YIG)ⷧ⭷ࡢ☢ᛶࢆゎᯒࡋࡓࠋࡑࡢ⤖ᯝࠊヨᩱ࡬ࡢ X⥺ධᑕゅࡀ῝ࡃ࡞ࡿ࡟ࡘࢀ࡚ࠊFe ࡢ XMCD ಙྕᙉᗘࡀቑ኱ࡋࡓࠋࡇࢀࡣࠊPt/YIG ⏺㠃௜㏆࡟࠾࠸࡚ࠊYIG ୰ࡢ Fe ࡢ☢Ẽ࣮࣓ࣔࣥࢺࡀᑠࡉࡃ࡞ࡗ࡚࠸ࡿࡇ࡜ࢆ♧၀ࡍࡿࠋ࣮࣮࢟࣡ࢻ㸸 X ⥺☢Ẽ෇஧Ⰽᛶࠊ⇕㟁ᮦᩱࠊYIG⫼ᬒ࡜◊✲┠ⓗ㸸
Y3Fe5O12 (YIG; yttrium iron garnet) ᇶᯈ࡟ Pt ⷧ⭷ࢆ✚ᒙࡉࡏࡓ࠸ࢃࡺࡿࢫࣆࣥࢺࣟࢽࢡࢫࢹࣂ࢖ࢫࡣࠊ☢ሙࢆ༳ຍࡋ࡞ࡀࡽ ᗘᕪࢆ୚࠼ࡿ࡜⇕㉳㟁ຊࢆ⏕ࡌࡿ[1]ࠋࡑࡢᛶ㉁࠿ࡽࠊ᪂ࡋ࠸⇕Ⓨ㟁⣲Ꮚ࡜ࡋ࡚ࡢ฼⏝ྍ⬟ᛶࡀ࠶ࡿࡤ࠿ࡾ࡛࡞ࡃࠊ☢Ẽࢺࣥࢿࣝ᥋ྜ㸦MTJ; magnetic tunnel
junction㸧ࡋࡓ⣲Ꮚࡢ㧗࿘Ἴ࡟ᑐࡍࡿ㧗Ⓨ᣺≉ᛶ࠿ࡽࠊ࣑ࣜἼ㟁ἼࡢⓎ᣺⣲Ꮚ࡜ࡋ࡚ࡢ฼⏝ྍ⬟ᛶࡶ᳨ウࡉࢀ࡚࠸ࡿࠋࡇࡢࡼ࠺࡟☢ᛶయ࡜㠀☢ᛶయࡢ✚ᒙ⭷࡛ᵓᡂࡉࢀࡿࢫࣆࣥࢺࣟࢽࢡࢫࢹࣂ࢖ࢫ⣲Ꮚࡢ≉ᛶ࡟ࡣࠊ⭷ࡢᵓ㐀ࡸ☢Ẽ≉ᛶࡀᙉࡃᙳ㡪ࡍࡿ࡜⪃࠼ࡽࢀ࡚࠸ࡿࠋࡋ࠿ࡋࢼࣀ࣓࣮ࢺ࣮ࣝ࢜ࢲ࣮ࡢ⭷୰ࡢ☢ᛶホ౯ࡣᅔ㞴࡞ࡓࡵࠊ⭷ࡢᵓ㐀࡜☢Ẽ≉ᛶࡢ㛵ಀࡣ୙᫂ࡔࡗࡓࠋᨺᑕග X ⥺ࢆ⏝࠸ࡓ X ⥺☢Ẽ෇஧Ⰽᛶ ᐃ㸦XMCD; X-ray Magnetic Circular Dichroism㸧ࡣඖ⣲㑅ᢥᛶࡀ࠶ࡾࠊヨᩱࢆᵓᡂࡍࡿඖ⣲ẖࡢ☢ᛶࢆほ ྍ⬟࡛࠶ࡿࠋࢫࣆࣥࢺࣟࢽࢡࢫࢹࣂ࢖ࢫ࡟ᑐࡋ࡚ࠊXMCDᐃ࡛ Pt ࡜ Fe ࡢ☢ᛶࢆㄪ࡭ࡓ⤖ᯝࡀሗ࿌ࡉࢀ࡚࠸ࡿ[2, 3]ࠋࡋ࠿ࡋࠊ⾲㠃࣭⏺㠃௜㏆ࡢ☢ᛶࢆㄪ࡭ࡓ౛ࡣሗ࿌ࡉࢀ࡚࠸࡞࠸ࠋࡑࡇ࡛ࠊᮏሗ࿌࡛ࡣ XMCD ࡢゅᗘ౫Ꮡᛶ ᐃࢆᐇ᪋ࡋࠊࢫࣆࣥࢺࣟࢽࢡࢫࢹࣂ࢖ࢫࡢ⾲㠃࣭⏺㠃௜㏆ࡢ☢ᛶࢆㄪ࡭ࡿࡇ࡜ࢆ┠ⓗ࡜ࡋࡓࠋᐇ㦂㸸ᐃࡋࡓヨᩱࡣࠊ10 mm10 mm1mm ࡢ YIG ከ⤖ᬗᇶᯈ㸦pYIG)ࠊ࠾ࡼ
ࡧ Pt/pYIGࠊPt/Fe/pYIG ࡢ 3 ヨᩱࡔࡗࡓࠋ࠸ࡎࢀࡢヨᩱࡶࠊPt ᒙࡢཌࡉࡣ 1nmࠊFe ᒙࡢཌࡉࡣ 0.5 nm ࡔࡗࡓࠋࡉࡽ࡟ࠊᶆ‽ヨᩱ࡜ࡋ࡚ Fe ⟩࡜ࣂࣝࢡࡢ YIG ࢆ ᐃࡋࡓࠋXMCDᐃࡣSPring-8 ࡢ BL16XU㸦ࢧࣥࣅ࣮࣒㸧࡟࠾࠸࡚ᐇ᪋ࡋࡓࠋ ᐃࡢࢭࢵࢺ࢔ࢵࣉࢆᅗ 1 ࡟♧ࡍࠋ࢔ࣥࢪ࣮ࣗࣞࢱ࠿ࡽᨺ
ᅗ 1 XMCD ࡢ ᐃ㓄⨨ᅗࠋୖ࠿ࡽぢࡓᅗ࡛ࠊヨᩱࡣฟࡉࢀࠊSi(111)஧⤖ᬗศගჾ࡛༢Ⰽ໬
⦪⨨ࡁ࡟㓄⨨ࡋࡓࠋ㸦ᅗࡣ XMCDm ࡢ ᐃ㓄⨨ᅗ࡛ࠊࡋࡓ┤⥺㸦Ỉᖹ㸧೫ගࡢ X ⥺ࢆࠊࢲ࢖
XMCDp ࡣእ㒊☢ሙ Hex ࡢྥࡁࡀ㏫࡟࡞ࡿ㸧ࣖࣔࣥࢻ఩┦Ꮚࢆ⏝࠸࡚ࠊᕥᅇࡾࡲࡓ
ࡣྑᅇࡾࡢ෇೫ග X ⥺࡟ኚ᥮ࡋࡓࠋ
⏕ᡂࡋࡓ෇೫ග X ⥺ࢆࢫࣜࢵࢺ࡛⦪ 0.2 mm  ᶓ 0.1 mm ࡟ᡂᙧࡋࠊヨᩱ࡟↷ᑕࡋࡓࠋⷧ⭷ヨᩱ࡟ࡣࠊࣜࣥࢢ≧ࡢ Nd2Fe14B Ọஂ☢▼ࢆᑐྥࡉࡏ࡚ X ⥺ࡢධᑕ᪉ྥ࡟⣙ 0.1 T ࡢ㟼☢ሙࢆ༳ຍࡋࡓࠋࢩࣜࢥࣥࢻࣜࣇࢺ᳨ฟჾ㸦SDD㸧ࢆ⏝࠸࡚ࠊヨᩱ࠿ࡽᨺ䠉㻞㻠㻟䠉SPring-8/SACLA ฼⏝◊✲ᡂᯝ㞟

Section Bᅗ 2 Pt/pYIG ࡜ Pt/Fe/pYIG ࡢ X ⥺཯ᑕ⋡ࣉࣟࣇ࢓࢖ࣝࠋX ⥺ࡢἼ㛗ࡣ 0.15406 nm㸦Cu KĮ㸧࡛ࠊᶓ㍈ࡣἼᩘ Qࠊ⦪㍈ࡣ཯ᑕ⋡ᙉᗘࡢᑐᩘ R ࢆ⾲ࡍࠋ඲཯ᑕ⮫⏺ゅTc ࡣ 0.406 nm-1 ࡛࠶ࡿࠋฟࡉࢀࡿ⺯ග X ⥺ࢆィ ࡋࠊᕥྑ෇೫ග࡟ᑐࡍࡿ X ⥺྾཰ࢫ࣌ࢡࢺࣝ(XAFS)ࢫ࣌ࢡࢺࣝ [IL(E),IR(E)]ࢆ ᐃࡋࡓࠋ ᐃࡋࡓ XAFS ࢫ࣌ࢡࢺࣝ࠿ࡽࠊᘧ XMCDm(E) = [IL(E) - IR(E)] / [IL(E) + IR(E)]࡟ࡼࡾ XMCD ࢫ࣌ࢡࢺࣝࢆồࡵࡓࠋࡉࡽ࡟ࠊXMCD ಙྕᙉᗘࡀᚤᙅ࡞ሙྜࠊᗄఱᏛⓗ㓄⨨࡞࡝࡟ࡼࡾࢫ࣌ࢡࢺࣝࡀṍࡳࠊṇ☜࡟ゎᯒ࡛ࡁ࡞࠸ྍ⬟ᛶࡀ࠶ࡿࠋShimizu ࡽࡣࠊ☢ሙ࡜೫ග≧ែࢆ཯㌿ࡉࡏࡓ ᐃ࡛ṍࡳࢆゎᾘ࡛ࡁࡿࡇ࡜ࢆ♧ࡋࡓ[4]ࠋࡑࡇ࡛ࠊ௒ᅇࡢ ᐃ࡛ࡣ༳ຍ☢ሙࡢ᪉ྥࢆኚ࠼ࡓ㓄⨨࡛ XMCD ᐃࡋ [XMCDm(E)࡜ XMCDp(E)ࠊᅗ 1 ཧ↷]ࠊᘧ [XMCDm(E) – XMCDp(E)] /[XMCDm(E) + XMCDp(E)] ࡟ࡼࡾࠊ᭱⤊ⓗ࡞ Fe K ྾཰➃ࡢ XMCD ࢫ࣌ࢡࢺࣝࢆồࡵࡓࠋXMCDᐃࡍࡿ X ⥺ࡢධᑕゅᗘࡣࠊ࠶ࡽ࠿ࡌࡵ ᐃࡋࡓ X ⥺཯ᑕ⋡ࣉࣟࣇ࢓࢖ࣝ࠿ࡽỴᐃࡋࡓ㸦ᅗ 2㸧ࠋᐃࡋࡓ᭱పゅ 0.25q࡜᭱㧗ゅ 0.35q࡟࠾ࡅࡿ X ⥺ࡢ౵ධ㛗ࡣࠊX ⥺཯ᑕ⋡ࢫ࣌ࢡࢺࣝࢩ࣑࣮ࣗࣞ
ࢩࣙࣥ[5, 6] ࠿ࡽࡑࢀࡒࢀ 3 nm ࡜ 20 nm ࡜ぢ✚ࡶࡽࢀࡓࠋỴᐃࡋࡓྛゅᗘ࡟࠾࠸࡚ࠊXAFS ࢫ࣌ࢡࢺࣝ࡜ XMCD ࢫ࣌ࢡࢺࣝࢆ ᐃࡋࡓࠋ⤖ᯝ࠾ࡼࡧ⪃ᐹ㸸
ᅗ 3 ࡟ྛヨᩱࡢ XANES ࢫ࣌ࢡࢺࣝࡢධᑕゅᗘT౫Ꮡᛶࢆ♧ࡍࠋධᑕゅࡀ῝ࡃ࡟࡞ࡿ࡟ࡘࢀ࡚ࠊ྾཰➃࢚ࢿࣝࢠ࣮ࡀప࢚ࢿࣝࢠ࣮ഃ࡟ࢩࣇࢺࡋࡓࠋ୍᪉ࠊ7.108 keV ௜㏆ࡢࣉ࢚ࣜࢵࢪࣆ࣮ࢡᙧ
≧ࡣኚ໬ࡋ࡞࠿ࡗࡓࠋࡇࢀࡽࡢ⌧㇟ࡣࠊYIG ࡢᒁᡤᵓ㐀ࡣኚ໬ࡋ࡞࠸ࡀࠊ㓟⣲Ḟᦆ࡞࡝ࡀᏑᅾࡍࡿྍ⬟ᛶࢆ♧၀ࡍࡿࠋᅗ 4 ࡟྾཰➃㧗ࡉࡀ 0.5 ࡟࡞ࡿ࢚ࢿࣝࢠ࣮㸦E0㸧ࡢධᑕゅ౫Ꮡᛶࢆ♧ࡍࠋヨᩱ⾲㠃ഃࡢ྾཰➃࢚ࢿࣝࢠ࣮ࡣࣂࣝࢡࡢ YIG ࡟㏆ࡃࠊゅᗘࡀ῝ࡃ࡞ࡿ࡟ࡘࢀ࡚ప౯ᩘഃ࡟⣙ 2eV ࢩࣇࢺࡋࡓࠋࡇࢀࡣࠊYIG ࡢ⤖ᬗᵓ㐀ኚ໬ࠊࡲࡓࡣ㟁Ꮚᵓ㐀ኚ໬ࡀᐤ୚ࡋ࡚࠸ࡿ࡜⪃࠼ࡽࢀࡿࠋYIG ࡢ⤖ᬗᵓ㐀ኚ໬࡟㛵ࡋ࡚ࡣࠊ㝧㟁Ꮚᾘ⁛ ᐃ࠿ࡽ♧၀ࡉࢀࡓ✵ᏍࡢᏑᅾࡀᐤ୚ࡋ࡚࠸ࡿྍ⬟ᛶࠊࡲࡓ㟁Ꮚᵓ㐀ࡢኚ໬࡟㛵ࡋ࡚ࡣࠊ༙ᑟయ᥋ྜ⏺㠃࡟࠾ࡅࡿࣂࣥࢻࡢኚ໬ࡀᐤ୚ࡋ࡚࠸ࡿྍ⬟ᛶࡀ⪃࠼ࡽࢀࡿࠋᅗ 3 ྛゅᗘ࡟࠾ࡅࡿ XAFS ࢫ࣌ࢡࢺࣝࠋࢫ࣌ࢡࢺࣝࡣ྾཰➃㧗ࡉPࡀ 1 ࡟࡞ࡿࡼ࠺࡟つ᱁໬ࡋࡓࠋࡲࡓࠊP䠙0.5 䛻䛺䜛䜶䝛䝹䜼䞊䜢䠡䠌䛸ᐃ⩏䛧䛯䠄ᅗ୰䛻䠢䡁⟩䛾 E0 䜢♧䛩䠅䚹

ᅗ 4 E0 ࡢධᑕゅᗘ౫Ꮡᛶࠋࡇࡇ࡛ E0 ࡣつ᱁໬ࡋࡓ XANES ࢫ࣌ࢡࢺࣝࡢ྾཰➃㧗ࡉ
ࡀ 0.5 ࡟࡞ࡿ࢚ࢿࣝࢠ࣮㸦ᅗ 2 ཧ↷㸧ࠋཧ↷ヨᩱ࡜ࡋ࡚ࠊFe ⟩࡜ YIG ࡢ⤖ᯝࡶ♧ࡍࠋ䠉㻞㻠㻠䠉SPring-8/SACLA ฼⏝◊✲ᡂᯝ㞟

Section Bᅗ 5 ࡟ྛヨᩱࡢ௦⾲ⓗ࡞ゅᗘ࡛ ᐃࡋࡓXMCD ࢫ ࣌ ࢡ ࢺ ࣝ ࢆ ♧ ࡍ ࠋ Pt/YIG ヨ ᩱ ࠊPt/Fe/YIG ヨᩱ࡜ࡶ࡟ 7.105 keV – 7.11 keV ௜㏆࡟ᖜࡢ⊃࠸ XMCD ಙྕࡀほ ࡉࢀࡓࠋࡇࢀࡣࠊ㐣ཤࡢሗ࿌࠿ࡽ YIG ୰ࡢ Fe ࡟ࡼࡿ XMCD ಙྕ࡛࠶ࡿ࡜ุ᩿ࡋࡓ[2]ࠋࡲࡓࠊ୧ヨᩱ࡜ࡶ࡟ 7.11keV – 7.13 keV ࡟ᖜࡢᗈ࠸ XMCD ࢫ࣌ࢡࢺࣝࡀほ ࡉࢀࡓࠋFe ⟩࡛ࡣ 7.115 keV – 7.13 keVࡢ㛫࡛ᖜࡢᗈ࠸ XMCD ࢫ࣌ࢡࢺࣝࡀほ ࡉࢀࡓࡀ㸦ᅗ 5 ୗ㸧ࠊFe ⟩ࡢ XMCD ࢫ࣌ࢡࢺࣝᙧ≧ࡣ YIG ヨᩱ࡜␗࡞ࡿࡢ࡛ࠊPt/YIG ヨᩱ࠾ࡼࡧ
Pt/Fe/YIG ヨᩱࡢ E > 7.11 keV ࡛ほ ࡉࢀࡓᖜࡢᗈ࠸ࢫ࣌ࢡࢺࣝࡣࠊFe ༢యࡢಙྕ࡛ࡣ࡞࠸࡜⪃࠼ࡽࢀࡿࠋヲ⣽࡞ཎᅉࡣ୙᫂ࡔࡀࠊ(1) ⏺㠃ࡢ≉␗࡞≧ែࡸ YIG ࡢ㟁Ꮚ≧ែࢆ཯ᫎࡋ࡚࠸ࡿྍ⬟ᛶࠊ(2)ᐃ⣔ࡢᑐ⛠ᛶࡢၥ㢟ࡀ⪃࠼ࡽࢀࡿࠋࡉࡽ࡟ࠊ௒ᅇ ᐃࡋࡓ Pt/Fe/YIG ヨᩱ࠿ࡽFe ᒙ࡟⏤᮶ࡍࡿ XMCD ࢫ࣌ࢡࢺࣝࡣほ ࡉࢀ࡞࠿ࡗࡓࠋࡇࢀࡣࠊFe ᒙࡀ㠀ᖖ࡟ⷧ࠸ࡓࡵ࡟XMCD ಙྕࡀᙅ࠸ࠊFe ᒙࡢ☢ᛶࡀᾘኻࡲࡓࡣ
ῶࡌ࡚࠸ࡿྍ⬟ᛶࡀ⪃࠼ࡽࢀࡿࠋ
ḟ࡟ࠊXMCD ಙྕᙉᗘࡢゅᗘ౫Ꮡᛶ࠿ࡽ YIG
୰ࡢ Fe ࡢ☢໬ኚ໬ࢆㄪ࡭ࡓࠋXMCD ಙྕࡀ᭱ࡶ኱ࡁࡃ࡞ࡿ E = 7.107 keV ௜㏆ࡢ XMCD ಙྕᙉᗘࡣࠊX ⥺ࡢධᑕゅࡀ 0.35°࡜ 0.25°ࡢ᫬࡛ࡑࢀࡒࢀ 0.002 ࡜ 0.001 ࡔࡗࡓࠋYIG ࡬ࡢ X ⥺ࡢ౵ධ㛗ࡣ 45.5 nm (0.35°)࡜ 4.5 nm (0.25°)࡞ࡢ࡛
㸦ᣓᘼෆࡣධᑕゅ㸧[5, 6]ࠊධᑕゅࡀ 0.35°ࡢ᫬ᅗ 5 ྛヨᩱࡢ XMCD ࢫ࣌ࢡࢺࣝࢆࣂࣝࢡࡢ≧ែ࡜⪃࠼ࡿ࡜ࠊ⾲㠃 4.5 nm ࡼࡾὸ࠸㡿ᇦࡢ☢໬ࡣࠊࣂࣝࢡࡢ⣙ 50%࡟࡞ࡗ࡚࠸ࡿ
ࡇ࡜ࢆ♧၀ࡍࡿࠋࡲࡓࠊ⾲㠃࡟࠾ࡅࡿ☢໬ࡢῶᑡࡣࠊYIG ࡢ㟁Ꮚ≧ែࡢኚ໬ࢆ཯ᫎࡋ࡚࠸ࡿྍ⬟ᛶࡀ⪃࠼ࡽࢀࡿࠋ
௒ᚋࡢㄢ㢟㸸
௒ᅇࡢ XMCD ᐃ࡛ࠊࢫࣆࣥࢺࣟࢽࢡࢫࢹࣂ࢖ࢫࡢ☢໬ࡢ῝ࡉ౫Ꮡᛶࢆゎᯒྍ⬟࡞ࡇ࡜ࡀ♧၀ࡉࢀࡓࠋࡋ࠿ࡋࠊᗄఱᏛⓗ࡞㓄⨨࡟ࡼࡿᙳ㡪࡜⪃࠼ࡽࢀࡿ XMCD ಙྕࡢṍࡳࡀ⏕ࡌࡓࡢ࡛ࠊᐃ㓄⨨ࡢ᭱㐺໬࡟ࡼࡾ XMCD ಙྕࡢṍࡳࡀ⏕ࡌ࡞࠸ࡼ࠺࡟ࡍࡿᚲせࡀ࠶ࡿࠋࡲࡓࠊඖ⣲㑅ᢥᛶࡣ↓࠸ࡶࡢࡢࠊⷧ⭷ࡢ☢໬ࢆ┤᥋ゎᯒࡍࡿᡭἲ࡜ࡋ࡚ࠊ೫ᴟ୰ᛶᏊ཯ᑕ⋡ ᐃࡢ┦⿵ⓗ฼⏝ࡀ᭷ຠ࡜⪃࠼ࡽࢀࡿࠋཧ⪃ᩥ⊩㸸[1] B. F. Miao, et al., Phys. Rev. Lett. 112, 236601 (2014).
[2] S. Geprägs, et al., Applied Physics Letters 101, 262407 (2012).
[3] Y. M. Lu, et al., Phys. Rev. Lett. 110, 147207 (2013).
[4] N. Shimizu, et al., J. Phys. Soc. Jpn. 73, 800 (2004).
[5] X-ray Interactions with matter, The Center for X-Ray Optics; http://henke.lbl.gov/.
[6] B.L. Henke, et al., , Atomic Data and Nuclear Data Tables 54, 181-342 (1993).

(Received: March 29, 2019; Accepted: July 16, 2019; Published: August 29, 2019䠉㻞㻠㻡䠉