Physics at Virginia

"X-ray and Neutron Scattering on Square Lattice Antiferromagnets: 214-nickelates and melilite Ba2CoGe2O7"

Rajesh Dutta , Institut fur Kristallographie, RWTH Aachen University
[Host: Despina Louca]

Neutron scattering and its complementary X-ray scattering techniques help to probe many novel and
exotic quantum phenomena in materials and here, two case studies on spin dynamics in square lattice
Heisenberg antiferromagnets (AFM) are highlighted. Doped 214 -nickelates have served as a model
compound to understand its spin and charge stripe correlation in homologous superconducting
layered 214 -cuprates since last two decades. There are many similarities between La-based and
Pr-based 214-nickelates in terms of static stripe phases which emerge upon doping but, La-based
214 -nickelates have been treated so far as quassi 2D-XY AFM because of its negligible out-of-plane
exchange interaction. However, in our recent studies using inelastic neutron scattering (INS) and
linear spin wave theory (LSWT) calculations we have observed a sizeable out-of-plane exchange
interactions and the corresponding 3D spin wave dispersion in Pr1.5Sr0.5NiO4 [1, 2]. Besides static
charge and spin stripe degrees of freedom in Pr2−xSrxNiO4+δ, oxygen ordering on top of it plays
an important role and we have shown that presence of spin stripe fluctuation is not a prerequisite
for the formation of static charge stripe [3]. Another model compound multiferroic Ba2CoGe2O7
serves as an upstanding platform to study in gernal square lattice quantum physics with (S ≥ 1
2 ) besides its unconventional metal-ligand d-p hybridization mechanism which is responsible for giant
magnetoelectric effects. Using INS under applied high magnetic fields, we have demonstrated that
easy-plane-type single-ion anisotropy (SIA) can be tunable under fields and SIA is responsible for
the changes in the optical modes and unconventional electromagnon modes in 3D anisotropic spin
dispersion [4].

[1] A. Maity, R. Dutta, and W. Paulus, Stripe discommensuration and spin dynamics of half-doped Pr3/2Sr1/2NiO4, Phys. Rev.
Lett. 124, 147202 (2020).
[2] R. Dutta, A. Maity, A. Marsicano, J. R. Stewart, M. Opel, and W. Paulus, Direct evidence for anisotropic three-dimensional
magnetic excitations in a hole-doped antiferromagnet, Phys. Rev. B 102, 165130 (2020).
[3] A. Maity, R. Dutta, and W. Paulus, Spin stripe fluctuations in antiferromagnetic Pr2−xSrxNiO4+δ, Phys. Rev. B 106,
024414 (2022).
[4] R. Dutta, H. Thoma, I. Radelytskyi, A. Schneidewind, V. Kocsis, Y. Tokunaga, Y. Taguchi, Y. Tokura, and V. Hutanu, Spin
dynamics study and experimental realization of tunable

Condensed Matter Seminar
Monday, February 20, 2023
3:30 PM
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