8 research outputs found
Divergent effects of static disorder and hole doping in geometrically frustrated b-CaCr2O4
The gallium substituted and calcium deficient variants of geometrically
frustrated b-CaCr2O4, b-CaCr2-2xGa2xO4 (0.02<= x<= 0.25) and b-Ca1-yCr2O4
(0.075<= y<= 0.15), have been investigated by x-ray powder diffraction,
magnetization and specific heat measurements. This allows for a direct
comparison of the effects, in a geometrically frustrated magnet, of the static
disorder that arises from non-magnetic substitution and the dynamic disorder
that arises from hole doping. In both cases, disturbing the Cr3+ lattice
results in a reduction in the degree of magnetic frustration. On substitution
of Ga, which introduces disorder without creating holes, a gradual release of
spins from ordered antiferromagnetic states is observed. In contrast, in the
calcium deficient compounds the introduction of holes induces static
ferrimagnetic ordering and much stronger perturbations of the b-CaCr2O4 host.Comment: 23 pages, 10 figure
Zigzag ladders with staggered magnetic chirality in the S=3/2 compound beta-CaCr2O4
The crystal and magnetic structures of the S = 3/2 chain antiferromagnet
beta-CaCr2O4 have been investigated by means of specific heat, magnetization,
muon relaxation and neutron powder diffraction between 300K and 1.5K. Owing to
the original topology of the Cr3+ magnetic lattice, which can be described as a
network of triangular ladders, equivalent to chains with nearest and
next-nearest neighbors interactions, evolution of the magnetic scattering
intensity in this compound evidences two magnetic regimes : for 21K < T < 270K,
a low-dimensionality magnetic ordering of the Cr3+ spins is observed,
simultaneously with a strong contraction of the ladder legs, parallel to c.
Below TN = 21K, a complex antiferromagnetic ordering is evidenced, with an
incommensurate propagation vector k = (0, 0, q) (q ~ 0.477 at 1.5K), as
exchange interactions between ladders become significant. This complex magnetic
ordering can be described as a honeycomb-like arrangement of cycloids, running
along c, with staggered chiralities. The experimental observation of this
staggered chirality can be understood by taking into account antisymmetric
Dzyaloshinskii-Moriya exchange terms.Comment: 9 figure