### Session J23: Focus Session: Cuprates and Nickelates

11:15 AM–2:15 PM, Tuesday, March 11, 2008
Morial Convention Center Room: 215

Sponsoring Units: DMP GMAG
Chair: John Tranquada, Brookhaven National Laboratory

Abstract ID: BAPS.2008.MAR.J23.4

### Abstract: J23.00004 : Detection of the Spin Reorientation and Glassy Dynamics in La$_{1.55}$Sr$_{0.45}$NiO$_4$

12:15 PM–12:27 PM

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#### Authors:

Sean Giblin
(ISIS, Rutherford Appleton Lab)

Paul Freeman
(ILL, France)

Dharmalingham Prabhakaran
(University of Oxford, UK)

Andrew Boothroyd
(University of Oxford, UK)

The magnetism of charge stripe ordered La$_{1.55}$Sr$_{0.45}$NiO$_4$ was studied by the combined techniques of neutron diffraction, muon spin relaxation and mass susceptibility. Magnetic ordering was observed at a lower temperature by muon relaxation than neutron diffraction, indicating a glassy transition to the ordered phase, in agreement with the susceptibility. Neutron diffraction determined a second magnetic transition that is observed by all techniques, to be a spin reorientation. On cooling below $T{\rm_{SR}} = 42$\, K the spins re-orientate from lying 33.7$\pm 0.6 ^{\circ}$ away from the stripe direction at 70\,K to 57.4 $\pm 0.4^ {\circ}$ at 10\, K. The magnetic order was observed by neutron diffraction to be of both anisotropic 3D and 2D (without any correlation on the $c$ axis) character. Muon relaxation confirmed this to be consistent with a single magnetically ordered spin stripe phase. The muon site associated with the spin stripe indicated critical behavior expected from a two dimensional magnetically ordered state, whereas the site associated with the charge stripe showed three dimensional critical behavior indicating spin frustration at the charge stripe.

To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2008.MAR.J23.4