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Register a new userA single-crystal neutron diffraction study on magnetic structure of the quasi-one-dimensional antiferromagnet SrCo2V2O8
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The magnetic structure of the spin-chain antiferromagnet SrCo2V2O8 is determined by single-crystal neutron diffraction experiment. The system undergoes magnetic long range order below T_N = 4.96 K. The moment of 2.16{mu}_B per Co at 1.6 K in the screw chain running along the c axis alternates in the c-axis. The moments of neighboring screw chains are arranged antiferromagnetically along one in-plane axis and ferromagnetically along the other in-plane axis. This magnetic configuration breaks the 4-fold symmetry of the tetragonal crystal structure and leads to two equally populated magnetic twins with antiferromagnetic vector in the a or b axis. The very similar magnetic state to the isostructural BaCo2V2O8 warrants SrCo2V2O8 another interesting half-integer spin-chain antiferromagnet for investigation on quantum antiferromagnetism.
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BaCo2V2O8 is a nice example of a quasi-one-dimensional quantum spin system that can be described in terms of Tomonaga-Luttinger liquid physics. This is explored in the present study where the magnetic field-temperature phase diagram is thoroughly established up to 12 T using single-crystal neutron diffraction. The transition from the Neel phase to the incommensurate longitudinal spin density wave (LSDW) phase through a first-order transition, as well as the critical exponents associated with the paramagnetic to ordered phase transitions, and the magnetic order both in the Neel and in the LSDW phase are determined, thus providing a stringent test for the theory.
The magnetic structure of CsCo2Se2 was investigated using single-crystal neutron diffraction technique. An antiferromagnetic transition with the propagation vector (0,0,1) was observed at T_N = 78 K. The Co magnetic moment 0.772(6) {mu}_B at 10 K pointing in the basal plane couples ferromagnetically in the plane which stacks antiferromagnetically along the c direction. Tuning and suppressing the interplane antiferromagnetic interaction may be crucial to induce the material to a superconducting state.
Polarised neutron diffraction measurements have been made on HoFeO$_3$ single crystals magnetised in both the [001] and [100] directions ($Pbnm$ setting). The polarisation dependencies of Bragg reflection intensities were measured both with a high field of H = 9 T parallel to [001] at T = 70 K and with the lower field H = 0.5 T parallel to [100] at T = 5, 15, 25~K. A Fourier projection of magnetization induced parallel to [001], made using the $hk0$ reflections measured in 9~T, indicates that almost all of it is due to alignment of Ho moments. Further analysis of the asymmetries of general reflections in these data showed that although, at 70~K, 9~T applied parallel to [001] hardly perturbs the antiferromagnetic order of the Fe sublattices, it induces significant antiferromagnetic order of the Ho sublattices in the $xmhyphen y$ plane, with the antiferromagnetic components of moment having the same order of magnitude as the induced ferromagnetic ones. Strong intensity asymmetries measured in the low temperature $Gamma_2$ structure with a lower field, 0.5 T $parallel$ [100] allowed the variation of the ordered components of the Ho and Fe moments to be followed. Their absolute orientations, in the 180degree domain stabilised by the field were determined relative to the distorted perovskite structure,. This relationship fixes the sign of the Dzyalshinski-Moriya (D-M) interaction which leads to the weak ferromagnetism. Our results indicate that the combination of strong y-axis anisotropy of the Ho moments and Ho-Fe exchange interactions breaks the centrosymmetry of the structure and could lead to ferroelectric polarization.
This paper presents results of a recent study of multiferroic CCO by means of single crystal neutron diffraction. This system has two close magnetic phase transitions at $T sub{N1}=24.2$ K and $T sub{N2}=23.6$ K. The low temperature magnetic structure below $T sub{N2}$ is unambiguously determined to be a fully 3-dimensional proper screw. Between $T sub{N1}$ and $T sub{N2}$ antiferromagnetic order is found that is essentially 2-dimensional. In this narrow temperature range, magnetic near neighbor correlations are still long range in the ($H,K$) plane, whereas nearest neighbors along the $L$-direction are uncorrelated. Thus, the multiferroic state is realized only in the low-temperature 3-dimensional state and not in the 2-dimensional state.
The crystal and magnetic structure of (La0.70Ca0.30)(CryMn1-y)O3 for y = 0.70, 0.50 and 0.15 has been investigated using neutron powder diffraction. The three samples crystallize in the Pnma space group at both 290 K and 5 K and exhibit different magnetic structures at low temperature. In (La0.70Ca0.30)(Cr0.70Mn0.30)O3, antiferromagnetic order with a propagation vector k = 0 sets in. The magnetic structure is Gx, i.e. of the G-type with spins parallel to the a-axis. On the basis of our Rietveld refinement and the available magnetisation data, we speculate that only Cr3+ spins order, whereas Mn4+ act as a random magnetic impurity. In (La0.70Ca0.30)(Cr0.50Mn0.50)O3 the spin order is still of type Gx, although the net magnetic moment is smaller. No evidence for magnetic order of the Mn ions is observed. Finally, in (La0.70Ca0.30)(Cr0.15Mn0.85)O3 a ferromagnetic ordering of the Mn spins takes place, whereas the Cr3+ ions act as random magnetic impurities with randomly oriented spins.
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