Study of the correlations and dynamics of spins in an XY-like spin-glass system (Ni0.40Mn0.60)TiO3
R. S. Solanki1*, S. -H. Hsieh1, G. Deng2, C. W. Wang3, H. Tonomoto4, Y. O. Yang5, J. S. Gardner2, T. Kimura4, F. -C. Chou5, C. H. Du1, W. F. Pong1
1Department of Physics, Tamkang University, Tamsui, Taiwan
2Australian Nuclear Science and Technology Organization, ANSTO, NSW, Australia
3National Synchrotron Radiation and Research Centre, NSRRC, Hsinchu, Taiwan
4Division of Materials Physics, Osaka University, Osaka, Japan
5Department of Physics, National Taiwan University, Taipei, Taiwan
* presenting author:Ravindra Singh Solanki,
Neutron scattering studies have been proved to be a powerful tool to study the static and dynamic magnetic correlations in the spin glass state of several systems [1-3]. Recently, an XY-like spin glass system (NixMn1-x)TiO3 for 0.40≤x≤0.48 has been reported to show linear magnetoelectric (ME) coupling [4, 5] and striking memory effects [6]. Generally, spin-glass systems do not show linear ME effect [4, 5]. In this work, we have carried out x-ray diffraction, magnetization and neutron scattering experiments on the single crystals of (Ni0.40Mn0.60)TiO3 (hereafter NMTO40) to investigate the correlations and dynamics of spins in the XY-like spin glass state of NMTO40. X-ray diffraction studies confirm excellent quality of the single crystal. Temperature dependent magnetization measurements reveal the signatures of spin-glass behavior in the NMTO40 with a freezing temperature of TSG≈9.14K. Further, Curie-Weiss fit to the high temperature magnetic susceptibility yields a Curie-Weiss temperature (θCW) ~ -91.28 K and effective moment (μeff) of 4.73 μB. The strongly negative value of θCW indicates dominant antiferromagnetic exchange interactions. Neutron powder diffraction experiments suggest the presence of a broad peak at finite q ≈ 0.6708 Å-1. The strong diffuse scattering is the signature of short range antiferromagnetic spin correlations. We have carried out elastic and inelastic neutron scattering studies on the single crystal around (0, 0, 1.5) reciprocal lattice point to study short range antiferromagnetic correlations. Elastic neutron scattering experiments have shown that magnetic diffuse scattering intensity starts to increase around 12K which is close to the TSG. Also, spin-spin correlation lengths (ξ) at 1.5K are 21.51 and 416.67 Å along interlayer and in-plane directions, demonstrating that magnetic correlations are quasi-2D and 3D, respectively, along the two directions. Inelastic neutron scattering results show the presence of quasielastic magnetic scattering profiles below TSG. The life time of dynamic correlations, τ~ ћ/ΓL, obtained from the full width at half maximums (FWHMs) (ΓL) of QENS profiles are about 1.716 and 2.518 psec at 9K along [0, 0, 1.52] and [0.01, 0.01, 1.50] directions. These experimental findings reveal that the short-range ordered antiferromagnetic clusters with short-lived spin correlations exist in the spin glass state of NMTO40 below TSG.
1. J. S. Gardner et al., Phys. Rev. Lett. 83, 211 (1999); 2. W. Bao et al., Phys. Rev. Lett. 91, 127005 (2003); 3. Y. Chen et al., Phys. Rev. B 72, 184401 (2005); 4. Y. Yamaguchi et al., Phys. Rev. Lett. 108, 057203 (2012); 5. Y. Yamaguchi et al., Nat. Comm. 4, 2063 (2013); 6. S. Chi et al., Phys. Rev. B 90, 144429 (2014).

Keywords: Magnetic Materials, Spin Glass, Neutron Scattering