86 research outputs found
Unravelling the complex magnetic structure of multiferroic pyroxene NaFeGe2O6: A combined experimental and theoretical study
Magnetic order and the underlying magnetic model of the multiferroic pyroxene
NaFeGe2O6 are systematically investigated by neutron powder diffraction,
thermodynamic measurements, density-functional bandstructure calculations, and
Monte-Carlo simulations. Upon cooling, NaFeGe2O6 first reveals one-dimensional
spin-spin correlations in the paramagnetic state below about 50 K, revealed by
magnetic diffuse scattering. The sinusoidal spin-density wave with spins along
the a-direction sets in at 13 K, followed by the cycloidal configuration with
spins lying in the (ac) plane below 11.6 K. Microscopically, the strongest
magnetic coupling runs along the structural chains, J1 ' 12 K, which is likely
related to the one-dimensional spin-spin correlations. The interchain couplings
J2 ' 3:8K and J3 ' 2:1K are energetically well balanced and compete, thus
giving rise to the incommensurate order in sharp contrast to other
transition-metal pyroxenes, where one type of the interchain couplings
prevails. The magnetic model of NaFeGe2O6 is further completed by the weak
single-ion anisotropy along the a-direction. Our results resolve the earlier
controversies regarding the magnetic order in NaFeGe2O6 and establish relevant
symmetries of the magnetic structures. These results, combined with symmetry
analysis, enable us to identify the possible mechanisms of the magnetoelectric
coupling in this compound. We also elucidate microscopic conditions for the
formation of incommensurate magnetic order in pyroxenes.Comment: 10 pages 10 figures, PRB(accepted
Weak ferromagnetism and spin reorientation in antiferroelectric BiCrO3
BiCrO3 is an antiferroelectric perovskite known to exhibit an unconventional spin reorientation transition between antiferromagnetic structures, accompanied by a large jump in weak ferromagnetism. Using a combination
of neutron powder diffraction, magnetometry, and symmetry analysis, we confirm the dominant G-type antiferromagnetic order below TN = 111 K and identify the magnetic phase transition with a spontaneous rotation of Cr3+
moments from the b axis to a particular direction in the ac plane. We demonstrate the role of antiferroelectric
displacements produced by the Bi3+ lone-pair electrons and octahedral rotations in establishing spin canting via
the antisymmetric Dzyaloshinskii-Moriya interaction. This mechanism results in weak ferromagnetism above
and below the spin-reorientation and explains the dramatic increase in net magnetization on cooling
Magnetic order in the frustrated Ising-like chain compound SrNiIrO
We have studied the field and temperature dependence of the magnetization of
single crystals of Sr3NiIrO6. These measurements evidence the presence of an
easy axis of anisotropy and two anomalies in the magnetic susceptibility.
Neutron powder diffraction realized on a polycrystalline sample reveals the
emergence of magnetic reflections below 75 K with magnetic propagation vector k
~ (0, 0, 1), undetected in previous neutron studies [T.N. Nguyen and H.-C zur
Loye, J. Solid State Chem., 117, 300 (1995)]. The nature of the magnetic ground
state, and the presence of two anomalies common to this family of material, are
discussed on the basis of the results obtained by neutron diffraction,
magnetization measurements, and symmetry arguments
First-order multi-k phase transitions and magnetoelectric effects in multiferroic Co3TeO6
A theoretical description of the sequence of magnetic phases in Co3TeO6 is
presented. The strongly first-order character of the transition to the
commensurate multiferroic ground state, induced by coupled order parameters
corresponding to different wavevectors, is related to a large magnetoelastic
effect with an exchange energy critically sensitive to the interatomic spacing.
The monoclinic magnetic symmetry C2' of the multiferroic phase permits
spontaneous polarization and magnetization as well as the linear
magnetoelectric effect. The existence of weakly ferromagnetic domains is
verified experimentally by second harmonic generation measurements
Magnetic frustration and spontaneous rotational symmetry breaking in PdCrO2
In the triangular layered magnet PdCrO2 the intralayer magnetic interactions
are strong, however the lattice structure frustrates interlayer interactions.
In spite of this, long-range, 120 antiferromagnetic order condenses at
~K. We show here through neutron scattering measurements under
in-plane uniaxial stress and in-plane magnetic field that this occurs through a
spontaneous lifting of the three-fold rotational symmetry of the nonmagnetic
lattice, which relieves the interlayer frustration. We also show through
resistivity measurements that uniaxial stress can suppress thermal magnetic
disorder within the antiferromagnetic phase.Comment: 9 pages, 9 figure
- …