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Some features of Single Layered Manganites La 1-x Sr 1+x MnO 4 G. Allodi, C. Baumann, B. Büchner, D. Cattani, R. De Renzi, P. Reutler.

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Presentation on theme: "Some features of Single Layered Manganites La 1-x Sr 1+x MnO 4 G. Allodi, C. Baumann, B. Büchner, D. Cattani, R. De Renzi, P. Reutler."— Presentation transcript:

1 Some features of Single Layered Manganites La 1-x Sr 1+x MnO 4 G. Allodi, C. Baumann, B. Büchner, D. Cattani, R. De Renzi, P. Reutler

2 Layered Structure SE 1 -x A 1+x MnO 4 Tetragonal I4/mmm b c a Ionic description of Mn-ions in a crystal field 3z 2 -r 2 x 2 -y 2 xz yz xy Orbital states of Jahn-Teller active ions are discribed as linear superpositions !!!

3 Layered Structure SE 1 -x A 1+x MnO 4 Tetragonal I4/mmm b c a :Mn 3+ a b c :Mn 4+ a b c Moritomo, PRB 51, 3297 (95) Bao, SSC 98, 55 (96) Bao, SSC 98, 55 (96)

4 P. Reutler, unpublished data, LLB Paris P. Reutler, unpublished data, LLB Paris Crystallographic aspects Distortion Strongly elongated octahedra D>1 for all x For comparison LaMnO 3 ( PRB57, 3189 (1998) ) Mn-O(1) (Å) 1.968, 1907 Mn-O(2) (Å) 2.178 Flop from out of plane to inplane orbitals at 1/8<x<1/4

5 d 3z 2 -r 2 unoccupied d xy,xz,yz Between two empty states no electron hopping possible localized  localized d 3z 2 -r 2 unoccupied d xy,xz,yz non-vanishing transfer integral Electron hopping possible delocalized  delocalized +d x 2 -y 2 or others Electronic origin for the transfer into orbitals lying in the ab- plane Neither d 3z²-r² nor d x²-y² states are true eigenstates

6 Electronic Properties Overall insulating behaviour No very CMR

7 FM exchange between Mn 3+ and Mn 4+ on delocalization La 1 Sr 1 MnO 4 (x=0) Under holedoping AFM exchange between two occupied t 2 g orbitals AFM? FM? Goodenough-Anderson-Kanamori Rules: AFM exchange between Mn 3+ and Mn 4+ on localized holes unoccupied t 2g occupied t 2g AFM !! Hopping possibile? Magnetism of La 1-x Sr 1+x MnO 4

8 AFM of La 1 Sr 1 MnO 4 and La 7/8 Sr 9/8 MnO 4 (0.5 0.5 0)+x(1 1 0) * 150 magnetic reflections taken at 5C.2, LLB, France ** high resolution powder neutron diffraction at 3T.2, LLB, France P. Reutler, unpublished Neutron diffraction C-type AFM In a body cell no magnetic couplings to next planes FRUSTRATION La 1 Sr 1 MnO 4 T N =127 K; 3.20* µ B /Mn La 7/8 Sr 9/8 MnO 4 T N ~65 K; 2.4** µ B /Mn

9 AFM of La 1 Sr 1 MnO 4 and La 7/8 Sr 9/8 MnO 4 B  c : nearly free spins at low temperatures B||c :only much smaller features at higher temperatures free xy- spins free xy- spins ~0.2 µ B /Mn La 1 Sr 1 MnO 4 La 7/8 Sr 9/8 MnO 4

10 C-Typ AFM longrange Order xy-Momente (0.2 µ B /Mn) ● Delocaliztion, but no metallicity ● Long range antiferromagnetism and simultaniously perpedincular ● Quasi free spins perpedincular to ordered moments Canting of AFM ordered spinmoments

11 μSR of La 7/8 Sr 9/8 MnO 4 Three contributions: - Slowly decaying Backround - Precession Ordered moments - NON DETECTED PARTdue to very fast depolarizing signal quasi-static disordered moments ~60% missing initial polarisation 4.2K TNTN The magnetism of La 7/8 Sr 9/8 MnO 4 is intrinsicallyinhomogeneous first datum

12 The rest of of La 1+x Sr 1-x MnO 4

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14 Shortrange static magnstism in La 0.6 Sr 1.4 MnO 4 by Muons Depolarization Curves described by Kubo-Tojabe-Function for T<18K

15 Zero field 55 Mn-NMR

16 Shortrange static magnstism in La 3/4 Sr 5/4 MnO 4 by Muons

17 Austauschwechselwirkung FM Austausch zwischen Mn 3+ und Mn 4+ bei Deloklisierung La 1 Sr 1 MnO 4 (x=0) Lochdotierung AFM Austausch zwischen zwei besetzen t 2 g Orbitalen AFM? FM? Goodenough-Anderson-Kanamori Regeln: AFM Austausch zwischen Mn 3+ und Mn 4+ bei lokalisierten Löchern unbesetzes t 2g besetzes t 2g AFM !! Hopping möglich?

18 Collective order of correlated orbitals Orbital form is parameterized by  on two sublattices A,B Order of orthogonal Orbitals on two sublattices A,B   collective order dynamic order  is fixed by further mechanism (on site anisotropy) Energy degeneracy for all  See also QF and orbital order: van den Brink, PRB 59, 6795 (99); Feiner, PRL 78, 2799 (97)


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