南京大学：单相多铁性物理与材料的理论与实验研究（讲稿）Multiferroicity - Our experiences beyond manganites，主讲：刘俊明）

+ M onezuelo Electric field Magnetic field ferroelectics(P) ferromagnet(M) ↑ electric field ◆magnetic field multiferroics (Px M) Magnetic field Electric field

國 Multiferroicity: Our experiences beyond manganites J.-M.Liu(刘俊明) Nanjing University Email:liujm@nju.edu.cn Group page http://pld.nju.edu.cn/

J. –M. Liu ( M. Liu (刘俊明) Nanjing University Nanjing University Email: liujm@nju.edu.cn liujm@nju.edu.cn Group page Group page http://pld.nju.edu.cn/ //pld.nju.edu.cn/ Multiferroicity: Our experiences beyond manganites

R1-xAx MnO3 多ma8ogo (disorder Metal Metal A 3z2-2 Insulator A ● C G 3x2.213y2-2 Insulator Nd CE ■ CxE1-x 0.2 0.4 0.6 ….0.8 hole concentration X Y.Tokura,RPP69,797 (2006)

Y. Tokura, RPP69, 797 (2006)

Content >Background motivations Origin of spiral spin order in manganites >Predictions of novel multiferroics >Phase competition and beyond Exchange bias in multiferroic heterostructure Summary perspectives

Content  Background & motivations  Origin of spiral spin order in manganites  Predictions of novel multiferroics  Phase competition and beyond  Exchange bias in multiferroic heterostructure  Summary & perspectives

Background:symmetry argument Magnetism Ferroelectricity Partially filled d shells Empty d shells break break Time reversal Space reversal symmetry symmetry t-→-t,M→-M x→-x,P→-P H-f(M,P)=f(-M,-P)=f(-M,P)=f(M,-P) N.A.Hill,Why are there so few magnetic ferroelectrics?J.Phys.Chem.B 104:6694(2000)

Background: symmetry argument ++ - ++ Partially filled d shells break Time reversal symmetry t-t, M-M N. A. Hill, Why are there so few magnetic ferroelectrics? J. Phys. Chem. B 104: 6694 (2000). Empty d shells break Space reversal symmetry x-x, P-P Magnetism Ferroelectricity H=f(M, P)=f(-M, -P) = f(-M, P)=f(M, -P)

Background:symmetry argument Mostovoy,PRL 96,067601(06) If spin order is spatially inhomogeneous, symmetry allows for the 3rd-order coupling POM and then P may appear. Φem(P,M ）= yP.[M(V·M)-(M·7)M+··], D=Φem+P2/2mE →P∝[(M·a)M-M(a.M)]

Background: symmetry argument If spin order is spatially inhomogeneous, symmetry allows for the 3rd-order coupling P∂M and then P may appear. =em+P2/2 Mostovoy, PRL 96, 067601 (06)

Background:spin configuration argument 1D chain magnet with the competition between NN FM coupling (J)and NNN AFM coupling (J)favors FSO if J'/J>1/4.(JPCM7,8605(1995) J'>0 J<0 Spin on the third site can't be consistent with the J AFM triangular-lattice AF favors FSO

Background: spin configuration argument  AFM triangular-lattice favors FSO.  1D chain magnet with the competition between NN FM coupling (J) and NNN AFM coupling (J ) favors FSO if |J /J|>1/4. (JPCM 7, 8605 (1995))

Background:structures and facts RMnO3 phases T.Goto et al. 100 PRL92,257201(2004) R=Nd paramagnetic g Sm Eu 50 eR兴 A-AF incommensurate-AF ↑ commen- ↑ RMnO3 surate 0 AF- 148 146 144 ↑ Mn-O-Mn bond angle(deg) ↓

Background: structures and facts T. Goto et al. RMnO3 phases PRL 92,257201 (2004) RMnO3 phases

Background:structures and facts 1.2 (a)35K 0.8 0.6 Tb/D T.Arima et al. 02 PRL96,097202(2006) -0.500.5 b axis 12 (b) 5K 1 0.8 Q.cp TbMnO; Sixe 04 0.2 0 -0.2 .1 -0.5 0 0.5 1 b axis

T. Arima et al. PRL 96, 097202(2006) TbMnO3 Background: structures and facts

Background:structures and facts a P//c a 600 1.10 0.8 (-6 nwa) (J mol-1 K-2) Specific heat/temperature 400 1.08 0.6 15K 9K 200 0.4 1.06 0 b 600 400 400 200 200 9 15K 0 0 0 20 30 40 0 Temperature(K) 0 Magnetic field (T) Kimura,Annu.Rev.Mater.Res.37,387,2007

Background: structures and facts Kimura, Annu. Rev. Mater. Res.37, 387, 2007