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

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 !!!

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)

P. Reutler, unpublished data, LLB Paris P. Reutler, unpublished data, LLB Paris Crystallographic aspects Distortion Strongly elongated octahedra D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) Flop from out of plane to inplane orbitals at 1/8<x<1/4

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

Electronic Properties Overall insulating behaviour No very CMR

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

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reflections taken at 5C.2, LLB, France ** high resolution powder neutron diffraction at 3T.2, LLB, France P. Reutler, unpublished Neutron diffraction C-type AFM In a body cell no magnetic couplings to next planes FRUSTRATION La 1 Sr 1 MnO 4 T N =127 K; 3.20* µ B /Mn La 7/8 Sr 9/8 MnO 4 T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

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

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

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

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

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

Zero field 55 Mn-NMR

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

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?

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)