Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMagnetic and magnetodielectric coupling anomalies in the Haldane spin-chain system Nd2BaNiO5
472
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report the magnetic, heat-capacity, dielectric and magnetodielectric (MDE) behaviour of a Haldane spin-chain compound containing light rare-earth ion, Nd2BaNiO5, in detail, as a function of temperature (T) and magnetic field (H) down to 2 K. In addition to the well-known long range antiferromagnetic order setting in at (T_N=) 48 K as indicated in dc magnetization (M), we have observed another magnetic transition near 10 K; this transition appears to be of a glassy-type which vanishes with a marginal application of external magnetic field (even H= 100 Oe). There are corresponding anomalies in dielectric constant as well with variation of T. The isothermal M(H) curves at 2 and 5 K reveal the existence of a magnetic-field induced transition around 90 kOe; the isothermal H-dependent dielectric constant also tracks such a metamagnetic transition. These results illustrate the MDE coupling in this compound. Additionally, we observe a strong frequency dependence of a step in T-dependent dielectric constant with this feature appearing around 25-30 K for the lowest frequency of 1 kHz, far below T_N. This is attributed to interplay between crystal-field effect and exchange interaction between Nd and Ni, which establishes the sensitivity of dielectric measurements to detect such effects. Interestingly enough, the observed dispersions of the T-dependent dielectric constant curves is essentially H-independent in the entire T-range of measurement, despite the existence of MDE coupling, which is in sharp contrast with other heavy rare-earth members in this series.
rate research
Read More
The Haldane spin-chain compound, Tb2BaNiO5, has been known to order antiferromagnetically below (T_N= ) 63 K. The present magnetic studies on the polycrystals bring out that there is another magnetic transition at a lower temperature (T_2= ) 25 K, with a pronounced magnetic-field induced metamagnetic and metaelectric behavior. Multiferroic features are found below T_2 only, and not at T_N. The most intriguing observation is that the observed change of dielectric constant is intrinsic and largest (e.g., about 18% at 15 K) within this Haldane spin-chain family, R2BaNiO5. Taking into account that this trend (the largest change for Tb case within this family) correlates with a similar trend in T_N (with the values of T_N being about 55, 58, 53 and 32 K for Gd, Dy, Ho and Er cases), we believe that an explanation usually offered for this T_N behavior in rare-earth systems is applicable for this behavior as well . That is, single-ion anisotropy following crystal-field splitting is responsible for this extraordinary magnetodielectric effect in this Tb case. To our knowledge, such an observation was not made in the past literature of multiferroics.
We have carried out dc magnetization (M), heat-capacity (C) and dielectric studies down to 2K for the compound GdCrTiO5, crystallizing in orthorhombic Pbam structure, in which well-known multiferroics RMn2O5 (R= Rare-earths) form. The points of emphasis are: (i) The magnetic ordering temperature of Cr appears to be suppressed compared to that in isostructural Nd counterpart, NdCrTiO5, for which the Neel temperature is about 21 K. This finding on the Gd compound suggests that Nd 4f orbital plays a role on the magnetism of Cr in contrast to a proposal long ago. (ii) Dielectric constant does not exhibit any notable feature below about 30 K in the absence of external magnetic field, but a peak appears and gets stronger with the application of external magnetic fields, supporting the existence of magnetodielectric coupling. (iii) The dielectric anomalies appear even near 100 K, which can be attributed to short-range magnetic-order. We also observe a gain in spectral weight below about 150 K in Raman spectra in the frequency range 150 to 400 cm-1, which could be magnetic in origin supporting short-range magnetic order. It is of interest to explore whether geometrically frustration plays any role on the dielectric properties of this family, as in the case of RMn2O5.
Reflection and transmission as a function of temperature have been measured on a single crystal of the magnetoelectric ferrimagnetic compound Cu$_{2}$OSeO$_{3}$ utilizing light spanning the far infrared to the visible portions of the electromagnetic spectrum. The complex dielectric function and optical properties were obtained via Kramers-Kronig analysis and by fits to a Drude-Lortentz model. The fits of the infrared phonons show a magnetodielectric effect near the transition temperature ($T_{c}sim 60$~K). Assignments to strong far infrared phonon modes have been made, especially those exhibiting anomalous behavior around the transition temperature.
We have investigated the dielectric anomalies associated with spin ordering transitions in the tetragonal spinel Mn$_3$O$_4$, using thermodynamic, magnetic, and dielectric measurements. We find that two of the three magnetic ordering transitions in Mn$_3$O$_4$ lead to decreases in the temperature dependent dielectric constant at zero applied field. Applying a magnetic field to the polycrystalline sample leaves these two dielectric anomalies practically unchanged, but leads to an increase in the dielectric constant at the intermediate spin-ordering transition. We discuss possible origins for this magnetodielectric behavior in terms of spin-phonon coupling. Band structure calculations suggest that in its ferrimagnetic state, Mn$_3$O$_4$ corresponds to a semiconductor with no orbital degeneracy due to strong Jahn-Teller distortion.
Macroscopic magnetic properties and microscopic magnetic structure of Rb$_2$Mn$_3$(MoO$_4$)$_3$(OH)$_2$ (space group $Pnma$) are investigated by magnetization, heat capacity and single-crystal neutron diffraction measurements. The compounds crystal structure contains bond-alternating [Mn$_3$O$_{11}$]$^{infty}$ chains along the $b$-axis, formed by isosceles triangles of Mn ions occupying two crystallographically nonequivalent sites (Mn1 site on the base and Mn2 site on the vertex). These chains are only weakly linked to each other by nonmagnetic oxyanions. Both SQUID magnetometry and neutron diffraction experiments show two successive magnetic transitions as a function of temperature. On cooling, it transitions from a paramagnetic phase into an incommensurate phase below 4.5~K with a magnetic wavevector near ${bf k}_{1} = (0,~0.46,~0)$. An additional commensurate antiferromagnetically ordered component arises with ${bf k}_{2} = (0,~0,~0)$, forming a complex magnetic structure below 3.5~K with two different propagation vectors of different stars. On further cooling, the incommensurate wavevector undergoes a lock-in transition below 2.3~K. The experimental results suggest that the magnetic superspace group is $Pnma.1(0b0)s0ss$ for the single-${bf k}$ incommensurate phase and is $Pnma(0b0)00s$ for the 2-${bf k}$ magnetic phase. We propose a simplified magnetic structure model taking into account the major ordered contributions, where the commensurate ${bf k}_{2}$ defines the ordering of the $c$-axis component of Mn1 magnetic moment, while the incommensurate ${bf k}_{1}$ describes the ordering of the $ab$-plane components of both Mn1 and Mn2 moments into elliptical cycloids
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
