Approaching the true ground state of frustrated A-site spinels: A combined magnetization and polarized neutron scattering study

Nair, Harikrishnan; Brückel, Thomas; Voigt, Jörg; Fu, Zhendong; Su, Yixi

doi:10.1103/PhysRevB.89.174431

Journal Article

FZJ-2014-05836

Approaching the true ground state of frustrated A-site spinels: A combined magnetization and polarized neutron scattering study

Nair, H. (Corresponding Author)FZJ* ; Fu, Z.FZJ* ; Voigt, J.FZJ* ; Su, Y.FZJ* ; Brückel, T.FZJ*

2014
APS College Park, Md.

Physical review / B 89(17), 174431 (2014) [10.1103/PhysRevB.89.174431]

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Please use a persistent id in citations: http://hdl.handle.net/2128/8085 doi:10.1103/PhysRevB.89.174431

Abstract: We re-investigate the magnetically frustrated, diamond-lattice-antiferromagnet spinels FeAl2O4 and MnAl2O4 using magnetization measurements and diffuse scattering of polarized neutrons. In FeAl2O4, macroscopic measurements evidence a “cusp” in zero field-cooled susceptibility around 13 K. Dynamic magnetic susceptibility and memory effect experiments provide results that do not conform with a canonical spin-glass scenario in this material. Through polarized neutron-scattering studies, absence of long-range magnetic order down to 4 K is confirmed in FeAl2O4. By modeling the powder averaged differential magnetic neutron-scattering cross section, we estimate that the spin-spin correlations in this compound extend up to the third nearest-neighbor shell. The estimated value of the Landé g factor points towards orbital contributions from Fe2+. This is also supported by a Curie-Weiss analysis of the magnetic susceptibility. MnAl2O4, on the contrary, undergoes a magnetic phase transition into a long-range ordered state below ≈40 K, which is confirmed by macroscopic measurements and polarized neutron diffraction. However, the polarized neutron studies reveal the existence of prominent spin fluctuations co-existing with long-range antiferromagnetic order. The magnetic diffuse intensity suggests a similar short-range order as in FeAl2O4. Results of the present work support the importance of spin-spin correlations in understanding magnetic response of frustrated magnets like A-site spinels which have predominant short-range spin correlations reminiscent of the “spin-liquid” state.

Keyword(s): Basic research (1st) ; Key Technologies (1st) ; Others (1st) ; Fundamental Science (1st) ; Magnetism (2nd) ; Condensed Matter Physics (2nd)