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M O T SO KI IIIKU VA Clio ki 11/ VIETTAT hieu R: Nguyen to dat hicm T: NguyCn to kim loai chuyen tiep M, A: ki hiCu cho nguyen lo dimg thay the cho kim loai T ARR, ART, All: tifong irng la he so luang lac trao doi giua cac spin R, giua spin R va spin T, giua eac^spin T HRR, nRx, \\y\' lirang irng la he so Irircrng phan it'r cua phan mang dat hiern, giua cac phan mang va cua phan mang kim loai chuyen tiep ^ Ml', MR, MJ, M^.,r: lirang ung la mOmen tir phan mang kim loai chuyen tiep, momcn lij phan mang dctl hiem, momcn Itr 3d, momcn cam irng SR, S]-: momcn spin irng \6\ ion R va ion T Tc, TK;: tuong ling vcfi nhiet dp Curie, nhiet dp bti trCr ( X)- : \\t so lijr hoa phan inang T at : ki hieu cho nguyen lir hyb : lai hoa, ve sir lai hoa f.u : mot don vi cOng Ihire Tii: viet tat KHTN : Khoa hoc Tu nhien Bp KHCN & moi Irudng : Bp Khoa hoc Cong nghe va moi Iruofng TT KHTN & CN Quoc gia: Trung lam Khoa hoe Tir nhien va COng nghe Quoc gia HFFP: High Field Free Powder method: phuong phap m&u bOt rdi du6i lu Irucfng cao DOS: Density Of States: mM dp Irang thai NMR: Nuclear Magnetic Resonance method: phuang phap c6ng huang lijr hat nhan LT: Light Transition Elements: kim loai chuyen liep nhe (kim loai chuyen tiep dau day) HT: Heavy Transition Elements: kim loai chuyen tiep nang (kim loai chuyen liep cuoi day) XPS: X-ray Photoelectron Spectroscopy metliod: phuang phap phal xa quang dien MUCLUC Md din Trang Chuong I Mo men tijf va tucmg tac trao doi cac hgp chat lien kim loai dat hiem-kim loai chuyen tiep 1.1 Nhan xet chung 1.2 Mo hinh Campbell w6 cau hinh spin va tuang tac trao doi 4f-3d cac hop chat R-T 1.3 Hien tuang lai hoa va cau hinh spin cac hap chat R-T 1.3.1 Cac trang thai lai 1.3.2 Miic dp lai hoa phu thuoc vao nong dp dat hiem 1.3.3 Mo men tu cam ling 5d va su phu thupc ciia no vao n6ng dp dat hiem 8 10 |j 1.3.4 Ca che tuang tac trao ddi 4f-3d va sir phu thupc ciia cucfng dp tuang tac 3d-4f vao nong dp dat hiem 1.4 Mot so khao sat thuc nghiem ve tuang tac trao doi cua cac hap chat R-T dira tren cac phep xac dinh nhiet trat tu va phep dp tij" hoa bao hoa 1.5 Mo hinh hoa tri tir 12 14 17 1.6 Ket luan chuang Chirang n Cac phuang phap nghien cu*u 23 2.1 Cac phuang phap thuc nghiem 23 2.1.1 Phuang phap tao mSu 23 2.1.2 Dotijdp 24 2.1.3 He ph6 Mossbauer 26 2.1.3.1 Hieu ung Mossbauer 26 2.1.3.2 Kha nang quan sat ph6 Mossbauer 26 2.1.3.3 Cac tuang tac sieu tinh te c6 ihi quan sat 27 2.1.3.4 Cac tham so ca ban cua he ph6 hap thii 28 Mossbauer 2.1.4 Cac phuang phap thirc nghiem khac: 2.1.4.1 Phan tich gian d6 nhieu xa Ranghen (X- Ray) 29 29 2.1.4.2 Do tir a nhiet dp thap tir trudng cao 29 2.1.4.3 ChupanhSEM 29 2.2 Xac dinh he so tuang tac trao doi 2.2.1 Xac dinh he so tuong tac trao doi (A^y) cac hap chat R-T 2.2.1.1 Mo ta tuang tac trao doi phep gan dung trucrng phan tir 2.2.1.2 Xac dinh dp Ian ciia tuang tac trao d6i tiJ" nhiet dp trattLr(Tc) ' ' 2.2.1.3 Xac dinh Ian tuang tac trao doi tij nhiet bii tru(TJ 2.2.2 Xac dinh gia tri nhiet dp chuydn pha T^ bang duang cong tir nhiet 29 29 29 30 32 32 33 2.2.3 Xac dinh gia tri momen spin thuan t\x hieu dung 2.3 Ket luan chuang ^^ Chuang i n Nghien ciJu tinh chat ti^ va tuang tac trao d6i 34 cac hop chat R(Fe|.^Ti^)2 3.1 Ma dau 34 3.2 Cau true tinh th^ 38 3.3 Nghien ciJu Mossbauer 41 3.4 Tudp 46 3.4.1 Tir dp bao hoa a T = 4,2 K 46 3.4.2 Cac duang cong tu nhiet 49 3.5 Thao luan cac ket qua thuc nghiem 53 3.5.1 So sanh sir thay doi cua truing sieu tinh te va momen tiJ M^ 53 3.5.2 Hoa tri tij* 54 3.5.3 He so tuang tac trao ddi 3d-4f (Ap.-p) 56 3.6 Ket luan chuang Chuang IV Nghien cu*u tinh chat tij va tuang tac trao doi 59 60 cac hop chat he R(Fe,.^Tij3 4.1 Ma dau 60 4.2 Cau true tinh the ciia cac hap chat R(Fe,.^Tij3 62 4.3 Tudp bao hoa a T = 4,2 K 64 4.4 Duang tir nhiet va nhiet dp Curie 66 4.5 Phan tfch cac ket qua va thao luin 68 4.6 Ket luan chuang 71 Chuang V Nghien cuu anh huang ciia nguyen to thay the len tinh chat ^2 ttrva tuang tac trao doi mot so hgp chat R(T,M),2 5.1 Nhirng nhan xet chung 5.2 Cac nghien ciru thuc nghiem tren he hgp chat RFe|2.xV^ (R = Gd,Y va Lu) 72 80 5.2.1 Ket qua phan tich nhieu xa tia X 80 5.2.2 Nhiet dp Curie 82 5.2.3 Momen tiJ phan mang Fe cac hgp chat LuFei2.xVx §4 5.2.4 Tuang tac trao doi giira cac phan mang (AcdPe) 85 5.2.5 Nhan xet cac ket qua thuc nghiem gg 5.3 Cac nghien cixu thirc nghiem tren he hgp chat RCoi2.xV^ gg 5.4 Ket luan chuang 03 Chuang VI Mot so nhan xet tdng quat v6 anh huang ciia hieu ung lai hoa len tinh chat til ciia cac hgp chat R-Fe 94 6.1 Momen tij" cam ung cac hgp chat R-T 94 6.2 Moi lien he giOa tuang tac trao doi 3d-4f va momen tir cam ting 99 6.3 Cuang dp tuang tac trao doi 3d-4f (ART) cac he hgp chat R-T va momen tij* cam ung 102 6.4 Anh huang ciia Si t6i tuang tac trao doi 3d-4f tren cac he hgp chat RFe,2.,Si, 103 6.5 Buc tranh lai hoa 3d(T)-3d(LT) va buc tranh lai hoa p-3d(T) 104 6.6 Ket luan chuang 107 Vn Ket luan chung 109 Danh muc c6ng trinh nghito cuu 110 Tai liau tham khao 112 Phuluc M6DAU Nghien cuu cac vat lieu lien kim loai dat hiem - kim loai chuydn tiep R-T, dac biet vdi T = Fe, Co va Ni la mot doi tupng c6 y nghla ca v6 khoa hpc ca ban va ung dung Cac nguyen to R c6 lap v6 dien tu 4/'kh6ng lap day voi dac tinh dinh xu cao Trong cac nguyen to nay, ca momen quy dao Ian momen spin deu dong gop vao momen tir nen chiing c6 di huong tij va tu giao Ian Tuy nhien, dac tfnh dinh xu ciia cac ham song 4/lai c6 tuong tac trao doi yeu, do nhiet dp trat tu ti^r thap (7^ < 300K) Ngupc lai, cac nguyen to kim loai T c6 quy dao J dupe ma rpng ve mat khong gian, gay nen tuong tac tir manh va nhiet dp Curie cao Cac vat lieu lien kim loai R-T vay ket hpp dupe cac uu diem v^ tir tinh ciia m6i nhom nguyen to R va T de tao nen cac vat lieu ixx c6 di huang tu Ian, dp tiJ giao kh6ng 16, tir dp va nhiet dp Curie cao Cac vat lieu nhu vay da dupe ung dung de che tao cac nam cham vTnh ciru cao cap (vi du nhu SmCo^, Nd2Fe,4B), cac vat lieu til' giao TbFe2 (Terfenol va (Tb,Dy)Fe2 (Terfenol-D), cac vat lieu ghi quang tu TbFeCo Tinh chat tir cua cac vat lieu kim loai R-T chii yeu dupe qui djnh bai tuang tac trao doi va di huang trucmg tinh thi Chung c6 the' dupe xem xet la vat lieu c6 hai phan mang R(4/) va T(3d} Trong cac hpp chat nay, noi chung c6 loai tuong tac trao doi: tuang tac R-R giua cac nguyen tii thupc phan mang dat hiem; tuo'ng tac T-T giiJa cac nguyen tu ciia phan mang T va tuang tac giua hai phan mang RT Tuong tac R-R la tuong tac trao d6i gian tiep; c6 ban chat va ca che kieu RKKY (Ruderman-Kittel-Kasuya-Yoshida) Tuong tac R-R rat yeu nen rat nhieu truong hpp c6 thi bo qua dupe Tuang tac T-T la tuang tac s4t tij" quyet dinh sir phu thupc nhiet dp ciia tu dp va gia tri nhiet dp Curie cao ciia cac hpp chat RT Dong gop ciia tuang tac 4f-3d{l\xc la tuong tac R-T) vao 7^- cung khong Ion, nhung tuong tac quy dinh cau true tir, xac dinh sir on dinh nhiet ciia momen tu 4fvk su phu thupc nhiet dp ciia di huang tir ciia phan mang dat hiem Do do, cac vat lieu nay, di huang tix tinh the c6 nguon goc bai ca hai phan mang tii' R va T O nhiet dp thap, di huang tii tinh the ciia dat hiem la Ion Di huang dupe chuyen tai tai phan mang T nha tuang tac R-T O nhiet dp cao, di huong ttr ciia cac kim loai chuyen tiep tra nen manh hon dj huang tii ciia cac kim loai dat hiem Luc tuong tac R-T lai dong vai tro chuyen tai lien ket di hu6ng tir phan mang T sang phan mang R Vi nhung ly vira neu, tuang tac trao doi 4f-3d da dupe nghien cuu manh me nhung nam tam muai ciia the ky 20 Tuang tac trao doi da dupe nghien cuu va xac dinh bang nhieu phuang phap thuc nghiem khac nhu: phuong phap tir dp tir truong cao tren cac m^u bpt rofi (High Field Free Powder - HFFP) [72,103], cac phuang phap nhiiu xa natron (Neutron Diffraction : ND), tan xa natron (Inelastic Neutron Scatterring: INS) [70,72], tij* nhiet dp Cuire (Tc) va nhiet dp bii trij (Ti^) [57], Cac ket qua thu dupe thuong kha phij hpp va do mot so qui luat bien doi ciia h^ng so tuang tac R-T (ART) d^ dugc tim thay Do la: (i) qui luat ARJ giam di X\x dau day den cuoi day dat hiem, (ii) qui luat A^j tang tang nong dp dat hiem va (iii) qui luat bien dcii cua Ap.j theo ban chat kim loai T (Fe, Co hay Ni) |57| Tren ca so cac ket qua thuc nghiem do, ca che ciia tuang tac 4f-3d cung da dupe khing dinh Do la ca che tuong tac gian tiep 4f-5d-3d, su phan cue ciia cac dien tir din 5d chii yeu xay hieu ung lai hoa giua cac dien tii 3d va 5d Co the nhan dinh rang hai muai nam viia qua la thai gian phat trien manh me ciia cac nghien cuu tren cac hpp chat lien kim loai R-T Mot nhung nguai ma dau cho huang nghien ciiu la giao su ngucfi Phap da qua c6 - giao su R Lemere Dudi su lanh dao ciia ong, phong thi nghiem tix hpc Louis Neel a Grenoble (Cong hoa Phap) da phat hien dupe nhilu tinh chat qui bau cua cac hpp chat R-Co [69] Cac nghien cuu Ian dSn sang cac phong thi nghiem khac tren the giai, Vien nghien cuu Van der Waals-Zeeman, Dai hpc Tong hpp Amsterdam (Ha Ian) cung la mot nhirng trung tam nghien cun manh me cac vat lieu Tuy nhien, cac nghien cuu c6 y nghla ung dung true tiep lai cong a My (nam cham Sm-Co, vat lieu tij giao Terfenol, vat lieu c6 hieu ling tir nhiet kh6ng 16) va a Nhat ban (nam cham Nd-Fe-B) Cac sang kien nh^m cai thien tinh chat tu ciia he hpp chat R-Fe lai dupe Coey (Ireland) de xuat: che tao cac vat lieu ditn ke dira tren phuang phap nitarit Trong khuon kho hpp tac quoc te, cac nghien cuu v6 he vat lieu R-T a Bp mon Vat ly Nhiet dp thap, Khoa Vat ly, Truong Dai hpc Tong hop Ha noi (nay la Truong Dai hpc Khoa hpc Tu nhien Dai hpc quoc gia Ha noi) cung da thu dupe nhi6u ket qua dang chii y tren cac nghien cuu ve di huang tu 3d, tuang tac 3d-4f, cac chuyen pha tir va cong nghe che tao cac nam cham dat hiem Noi chung, nghien cuu ca ban ve cac hop chat R-T hai chuc nam qua, ngoai mot so tinh loan cau true vijng, doi vai cac nghien cuu thuc nghiem, phuong phap thucfng dupe su dung nhieu nhat vAn la phuang phap thay the: nghien cuu su thay doi cua tinh chat tiJ" thay the cac ion khong ti^r tfnh (Y, La, Lu) vao phan mang 4f hoac thay the cac ion khong tir (Cu, Al, Si, B) vao phan mang 3d Cac nghien cuu nhu vay, chi dupe lien hanh va dupe hieu mot each don thuan theo hieu ling pha loang nong dp cac ion tix tinh mSu de lam giam truang phan tir, hoac de kiem tra mo hinh dan ion Mot so giai thich sau s^c hon CO di cap den hieu ung tij'-the tfch (thay doi ap suat tac dung len he m^u hoac dua vao su thay doi kfch thu6c cac ion thay the) Gdn day, vai cac c6 g^ng che tao va nghien cuu cac hop chat tij ciing moi hp 1:12 kieu RFe,2,xM^ va RCoj^.^M,, cac nguyen to M thay the cung chi dupe hieu va danh gia tren vai tro on dinh pha, anh huang ciia no den tfnh chat tir ciia cac hpp chat noi tren vSn ft dupe de cap Hien nay, tinh hinh nghien cuu cac hpp chat R-T c6 ve nhu dang chung lai, cac nha tu hpc tren the giai duang nhu tam b^ng long vcfi khoi lupng kien thuc khong 16 ma hp da kham pha hai chuc nam visa, qua mac dii vSn mot so cau hoi rat dan gian nhu: tai cuang dp tuang tac trao doi 4f-3d lai tang cac hpp chat (R,Y)-T, tuc la da lam loang nong dp cac ion tix [57]? Ngoai ra, mot cau hoi len han van c6 the dupe dat ra: neu xet ve vj trf bang he thong tu^n hoan va cau hinh cua cac lap v6 dien tii d, s thi cac nguyen to kim loai dat hiem c6 thi xem nhu cac nguyen to chuyin tiep ddu day nhu Sc, Ti, V (Light Trasition Elements - LT) Vay cac nguyen to LT c6 the c6 vai tro nhu cac dien tii" 5d cua nguyen to dat hiem cac hpp chat R-(Fe,LT) va R-(Co,LT) hay khong? Them vao do, cac nguyen to a kim c6 lap v6 vai cac dien tir p duac thay the vao cac hpp chat R-T se c6 vai tro nhu the nao? Theo quan niem cua chung toi, mot ca che tuong tac da dupe hieu la hieu ling lai hoa thi cac hpp chat ki6u nhu R-(Fe,LT) va R-(Co,LT), neu dupe nghien cuu, se la cac doi tuong rat qui di c6 co so kh^ng dinh them ca che cua tuang lac trao d6i tren nhi^u hp hop chat hon va vai nhieu kieu dien tu linh dpng han Do vay, luan an da chpn doi tupng nghien cuu la cac hpp chat R(Fei.^Tij2 R(Fe,,^TiJ3, RFe]2.^V^, RCoi2_xVx vai R = Gd, Lu va Y Mot so ket qua cua nhom nghien cuu tren mot so hpp chat khac nhu (Er,Y)Fe2, GdFei2-xSix cung se dupe neu lai di ban luan ket qua mot each tong quat Luan an dupe bo cue nhu sau: Sau phan ma dau la chuong Trong chuang nay, cac diem chinh \'i bien d6i momen tii va tuang tac trao d6i cac hop chat R-T da dupe nhin nhan duai quan niem ciia mo hinh lai hoa tren ca sa xem xet cac dai lupng vat ly Hen quan la he so tuong tac trao doi giua hai phan mang va momen tij trung binh cua hpp chat (trong sir phu thupc tham so hoa tri tir) Chuang trinh bay cac phuang phap CO lien quan t6i viec thu thap cac tham so thuc nghiem ma luan an su dung Cac chuang 3, va trinh bay cac thuc nghiem da dupe thuc hien tren cac he mau ma muc lieu nghien cuu cua luan an di Chuang trinh bay viec phan tfch cac ket qua thuc nghiem va cac ket luan ma luan an da rut tren ca so tra lai mot so cau hoi chua giai dap truac ve vai tro cua cac nguyen to kim loai chu}'en tiep nhe (Ti,V ) tham gia nhu phan thu ba cac hpp chat gia hai nguyen R-Fe-LT (R = Gd,Y,Lu) MOMEN TtrVA TUDNG Chuang L TAC TRAO DOI TRONG CAC HO? CHAT LIEN KIM LOAI DAT HIEM-KIM LOAI CHUYEN TIE? 1.1 Nhto xet chung Cac nguyen to dat hiem (R) va cac kim loai chuyen tiep 3d(T) c6 thi ket hop vai de tao cac hop chat lien kim loai dat hiem-kim loai chuyen tiep (R-T) vai mot so nong dp xac dinh, vi du cac he hpp chat RT2, RT3, RT*i' '•'iX.' B 61 W J » ^• -n'A )2«^^Tii( Bt 'KiC fXeJirW 8.00^ tXeH^'Sr m^ f3ft>)*rW S566 DtB>*f6s' lu rxffM'-Me^'' 6^ p^|*W m' tKe'^f^i U U S 824" 1,23 J5^' 1,1 ! m U I *?? iO^ ^ l ^ ' i^r!.a53* 'if uv>" hep 1.1 S ^ S P3 O 'c^ -^ OO OO 1^- ro '—^ -^^ 'oor^o -J •S «lr-l V-M-V i^tw-i » - ( > « WMr- r* Ci ••' r*r» C! *^ fl C* a> ^ > SC > cx ^ CO o I • • — • »—* * * ^ u.' tCTl: PC OO O « «~> -r^ 1) ,w> C/3 X to a> :S +1 •-I '5 -S >< + 4J - -^ 11 * - i ^ CO (/5 CJ E o o tu i3 ^ta o Q *-» c s < CO Phu luc S6' dien ttr hoa tri ( VE) Do am ditniX^^^), ban kinh tuang tac (R^) cho mot so nguyen to kim loai chuyen tiep va dat hiem (dSn tu* [63]) ^-^ «—I t> < -» — (— < ^ ,_: CL^ 5 (—^ ».o ,-; tr-* — -— — c« '^^ CI5 cr* t> —- r-4 Ca- c=i -v" «^ C_> ^ « OO -^^ '
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