اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدSlow Magnetic Order-Order Transition in the Spin Chain Antiferromagnet Ca3Co2O6
227
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Using powder neutron diffraction we have discovered an unusual magnetic order-order transition in the Ising spin chain compound Ca3Co2O6. On lowering the temperature an antiferromagnetic phase with propagation vector k=(0.5,-0.5,1) emerges from a higher temperature spin density wave structure with k=(0, 0, 1.01). This transition occurs over an unprecedented time-scale of several hours and is never complete.
قيم البحث
اقرأ أيضاً
Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO2, NaYbS2, and NaYbSe2, exhibit no long-range order down to the lowest measured temperatur
es and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS2 exhibits magnetic order below TN = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called stripe-yz type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce-Ce bonds. No structural lattice distortions are revealed below TN, indicating that the triangular lattice of Ce3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS2, based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure.
Partially-ordered magnets are distinct from both spin liquids and conventional ordered magnets because order and disorder coexist in the same magnetic phase. Here, we determine the nature of partial order in the canonical frustrated pyrochlore antife
rromagnet Gd$_2$Ti$_{2}$O$_{7}$. Using single-crystal neutron-diffraction measurements in applied magnetic field, magnetic symmetry analysis, inelastic neutron-scattering measurements, and spin-wave modeling, we show that its low-temperature magnetic structure involves two propagation vectors (2-$mathbf{k}$ structure) with suppressed ordered magnetic moments and enhanced spin-wave fluctuations. Our experimental results support theoretical predictions of thermal fluctuation-driven order in Gd$_{2}$Ti$_{2}$O$_{7}$.
Layered van-der-Waals 2D magnetic materials are of great interest in fundamental condensed-matter physics research, as well as for potential applications in spintronics and device physics. We present neutron powder diffraction data using new ultra-hi
gh-pressure techniques to measure the magnetic structure of Mott-insulating 2D honeycomb antiferromagnet FePS$_3$ at pressures up to 183 kbar and temperatures down to 80 K. These data are complemented by high-pressure magnetometry and reverse Monte Carlo modeling of the spin configurations. As pressure is applied, the previously-measured ambient-pressure magnetic order switches from an antiferromagnetic to a ferromagnetic interplanar interaction, and from 2D-like to 3D-like character. The overall antiferromagnetic structure within the $ab$ planes, ferromagnetic chains antiferromagnetically coupled, is preserved, but the magnetic propagation vector is altered from $(0:1:frac{1}{2})$ to $(0:1:0)$, a halving of the magnetic unit cell size. At higher pressures, coincident with the second structural transition and the insulator-metal transition in this compound, we observe a suppression of this long-range-order and emergence of a form of magnetic short-range order which survives above room temperature. Reverse Monte Carlo fitting suggests this phase to be a short-ranged version of the original ambient pressure structure - with a return to antiferromagnetic interplanar correlations. The persistence of magnetism well into the HP-II metallic state is an observation in seeming contradiction with previous x-ray spectroscopy results which suggest a spin-crossover transition.
A spin-1 Heisenberg model on trimerized Kagome lattice is studied by doing a low-energy bosonic theory in terms of plaquette-triplons defined on its triangular unit-cells. The model has an intra-triangle antiferromagnetic exchange interaction, $J$ (s
et to 1), and two inter-triangle couplings, $J^prime>0$ (nearest-neighbor) and $J^{primeprime}$ (next-nearest-neighbor; of both signs). The triplon analysis of this model studies the stability of the trimerized singlet (TS) ground state in the $J^prime$-$J^{primeprime}$ plane. It gives a quantum phase diagram that has two gapless antiferromagnetically (AF) ordered phases separated by the spin-gapped TS phase. The TS ground state is found to be stable on $J^{primeprime}=0$ line (the nearest-neighbor case), and on both sides of it for $J^{primeprime} eq 0$, in an extended region bounded by the critical lines of transition to the gapless AF phases. The gapless phase in the negative $J^{primeprime}$ region has a $sqrt{3}timessqrt{3}$ coplanar $120^circ$-AF order, with all the moments of equal length and relative angles of $120^circ$. The other AF phase, in the positive $J^{primeprime}$ region, is found to exhibit a different coplanar order with ordering wave vector ${bf q}=(0,0)$. Here, two magnetic moments in a triangle are of same magnitude, but shorter than the third. While the angle between the two short moments is $120^circ-2delta$, it is $120^circ+delta$ between a short and the long one. Only when $J^{primeprime}=J^prime$, their magnitudes become equal and the relative-angles $120^circ$. This ${bf q}=(0,0)$ phase has the translational symmetry of the Kagome lattice with isosceles triangular unit-cells. The ratio of the intensities of certain Bragg peaks, $I_{(1,0)}/I_{(0,1)} = 4sin^2{(frac{pi}{6}+delta)}$, presents an experimental measure of the deviation, $delta$, from the $120^circ$ order.
Using inelastic neutron scattering, we have observed a quasi-one-dimensional dispersive magnetic excitation in the frustrated triangular-lattice spin-2 chain oxide Ca3Co2O6. At the lowest temperature (T = 1.5 K), this magnon is characterized by a lar
ge zone-center spin gap of ~27 meV, which we attribute to the large single-ion anisotropy, and disperses along the chain direction with a bandwidth of ~3.5 meV. In the directions orthogonal to the chains, no measurable dispersion was found. With increasing temperature, the magnon dispersion shifts towards lower energies, yet persists up to at least 150 K, indicating that the ferromagnetic intrachain correlations survive up to 6 times higher temperatures than the long-range interchain antiferromagnetic order. The magnon dispersion can be well described within the predictions of linear spin-wave theory for a system of weakly coupled ferromagnetic chains with large single-ion anisotropy, enabling the direct quantitative determination of the magnetic exchange and anisotropy parameters.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
