Extremely Weakly Interacting ΔSz = 0 and ΔSz = 1 Excitations and Evidence for Fractional Quantization in a Magnetization Plateau: CeSb
Ames Laboratory; Physics and Astronomy
Ames Laboratory, Physics and Astronomy
Physical Review Letters
The plateau at 1/3 of the saturation magnetization Ms in the metamagnet CeSb is accompanied by a state of ferromagnetic layers of spins in an up-up-down sequence. We measured M and the specific heat C in the plateau, spin wave analyses of which reveal two distinct branches of excitations. Those with ΔSz=1 as measured by M, coexist with a much larger population of ΔSz=0 excitations measured by C but invisible to M. The large density of ΔSz=0 excitations, their energy gap, and their seeming lack of interaction with ΔSz=1 excitations suggest an analogy with astrophysical dark matter. Additionally, in the middle of the plateau three sharp jumps in M(H) are seen, the size of which, 0.15%Ms, is consistent with fractional quantization of magnetization per site in the down-spin layers.
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