Tuning the giant magnetoelastic transition in Ba3BiIr2O9 and Ba3BiRu2O9

Anomalous dielectric response in the triple perovskite ruthenate Ba3BiRu2O9

We have investigated the magnetic, dielectric and thermal properties of theSRu= 1 magnetic dimer Ba₃BiRu₂O₉, which is known to exhibit a spin-gap opening in conjunction with a first-order magneto-elastic phase transition at ∼175 K. Above the spin-gap temperature, the temperature dependence dielectric constant shows a peak like feature with pronounced frequency dependence. The critical slowing down behavior of this frequency dispersion suggests that a ferroelectric relaxor like electrical glassy state exists above the spin-gap opening temperature regime. The extermination of frequency dispersion-right at the magneto-elastic phase transition, is suggestive of a strong coupling between the lattice and charge-spin degrees of freedom in this triple perovskite system.

Large magnetodielectric coupling in the vicinity of metamagnetic transition in 6Hperovskite Ba3GdRu2O9

The 6H-perovskites Ba₃RRu₂O₉(R = rare earth element) demonstrate the magnetodielectric (MD) coupling as a manifestation of 4d-4fmagnetic interactions. Here, a detailed study of the structural, magnetic, heat capacity, and MD properties of the 6H-perovskite Ba₃GdRu₂O₉is reported. The signature of long-range antiferromagnetic (AFM) ordering ∼14.8 K (T_N) is evident from the magnetization and heat capacity studies. TheT_Nshifts towards the lower temperature side, apart from splitting in two with the application of the magnetic field. Field-dependent magnetization at 2 K shows three metamagnetic transitions with the opening of small hysteresis in different regions. A new transition atT₁emerges after the onset of the first metamagnetic transition. Complex magnetic behavior is observed in different magnetic field regions whereas these field regions themselves vary with the temperature. Dielectric response recorded at zero and 80 kOe field exhibits the development of MD coupling well aboveT_N. The MD coupling (∼4.5% at 10 K) is enhanced by 25% as compared to the Dy counterpart. Effect of complex magnetic behavior is also conveyed in the MD results where the maximum value of MD coupling is observed in the vicinity of 10 K (onset ofT₁) and near the second metamagnetic transition. Our investigation suggests that both Gd and Ru moments align simultaneously atT_N. Short-range magnetic ordering is possibly responsible for MD coupling aboveT_N.

Absolute calibration of the latent heat of transition using differential thermal analysis

We describe a simple and accurate differential thermal analysis setup to measure the latent heat of solid state materials undergoing abrupt phase transitions in the temperature range from 77 K to above room temperature. We report a numerical technique for the absolute calibration of the latent heat of transition without the need for a reference sample. The technique is applied to three different samples-vanadium sesquioxide undergoing the Mott transition, bismuth barium ruthenate undergoing a magnetoelastic transition, and an intermetallic Heusler compound. In each case, the inferred latent heat value agrees with the literature value within its error margins. To further demonstrate the importance of absolute calibration, we show that the changes in the latent heat of the Mott transition in vanadium sesquioxide (V₂O₃) remain constant to within 2% even as the depth of supersaturation changes by about 10 K in non-equilibrium dynamic hysteresis measurements. We also apply this technique for the measurement of the temperature-dependent specific heat.

Structure driven magnetic correlations and magnetodielectric coupling in 6H-perovskite Ba3DyRu2O9

The 6H-perovskites Ba₃(R/M)Ru₂O₉(R= rare Earth,M= transition metal) exhibit complex magnetism and have been extensively studied recently for their magnetodielectric (MD) properties. Here, we present a detailed study of structural, magnetic, thermodynamic and MD properties of a 6H-perovskite Ba₃DyRu₂O₉. This compound is found to undergo long range antiferromagnetic ordering below ∼5.8 K (T_N), along with the presence of metamagnetic transition at low temperatures. The heat capacity shows two additional anomalies at ∼28 K (T₁) and ∼33 K (T₂), besides the anomaly atT_N. Signature of these anomalies is also visible in the derivative of magnetization curve. The dielectric response also shows weak anomalies aroundT₁andT₂at zero field whereas anomaly atT₂gets suppressed at 80 kOe. The observed MD coupling of ∼2%-4% at 80 kOe field below ∼30 K temperature range, is among the highest values observed for the compounds of this family. Low temperature crystal structures of the compound show sharp distortion of Ru₂O₉octahedra nearT₂. Our study points toward the emergence of structurally driven spin correlations of Ru moments resulting in the observed MD coupling in this compound.