Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userQuantum continuum fluctuations in glassy perovskite Ca(Co$_{0.15}$Ru$_{0.85}$)O$_{3}$
56
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The quantum spin continuum and classical spin freezing, associated with a glassy state, represent two opposite extremes of a correlated electronic material. Here, we report the coexistence of a quantum spin continuum with a weak spin glass order in Co-doped CaRuO$_{3}$ perovskite near the chemical doping dependent metal-insulator transition boundary. Inelastic neutron measurements on Ca(Co$_{0.15}$Ru$_{0.85}$)O$_{3}$ at low temperature, $T$ = 1.5 K, reveal a continuum spectrum in the $Q-E$ space due to uncorrelated spin fluctuations. This persists across the glass transition at $T_G simeq$23 K. Furthermore, scaling of the dynamic susceptibility yields a very small scaling coefficient $alpha$ $simeq$ 0.1, suggesting extreme locality of the dynamic properties. The experimental results indicate the realization of a narrow regime where the distinction between continuum dynamic behavior and glass-like regimes is reduced.
rate research
Read More
The magnetic and ferroelectric properties of the multiferroic system Mn$_{1-x}$Co$_x$WO$_4$ (x=0.135, 0.15, and 0.17) are studied in magnetic fields $H_c$ oriented along the monoclinic $c$-axis. Mn$_{0.85}$Co$_{0.15}$WO$_4$, which is right at the phase boundary between two helical spin structures, exhibits a spontaneous sign change of the ferroelectric polarization when cooled in fields $H_c>$ 25 kOe. The origin of the ferroelectric polarization is studied and two magnetic exchange interactions contributing to the polarization are identified. In Mn$_{0.85}$Co$_{0.15}$WO$_4$ domains of the characteristic helical spin structures, known for x$<$0.15 and x$>$0.15, coexist and form domain boundaries. The contributions of the different domains to the global polarization are determined. The polarization reversal in Mn$_{0.85}$Co$_{0.15}$WO$_4$ can be explained by a combination of various contributions to the polarization and a strong correlation between magnetic domains of different helical spin orders resulting in a smooth transition across the domain walls which preserves the chirality of the spin spiral.
We investigate the evolution of magnetic excitations in Sr$_3$Ru$_2$O$_7$ using a three band tight binding model that takes into account the influence of Mn and Ti dopant ions. The effect of dopant ions on the Sr$_3$Ru$_2$O$_7$ band structure has been included by taking into account the dopant induced suppression of the oxygen octahedral rotation in the tight binding band structure and changes in electron occupation. We find that the low energy spin fluctuations are dominated by three wave vectors around Q=$((0,0),(pi/2,pi/2))$, and $(pi,0)$ which compete with each other. As the octahedral rotation is suppressed with increasing doping, the three wave vectors evolve differently. In particular, the undoped compound has dominant wavevectors at Q=$((0,0),(pi/2,pi/2))$, but doping Sr$_3$Ru$_2$O$_7$ leads to a significant enhancement in the spin susceptibility at the Q=$(pi,0)$ wavevector bringing the system closer to a magnetic instability. All the features calculated from our model are in agreement with neutron scattering experiments. We have also studied the effect of a c-axis Zeeman field on the low energy spin fluctuations. We find that an increasing magnetic field suppresses the AFM fluctuations and leads to stronger competition between the AFM and FM spin fluctuations. The magnetic field dependence observed in our calculations therefore supports the scenario that the observed nematic phase in the metamagnetic region in Sr$_3$Ru$_2$O$_7$ is intimately related to the presence of a competing ferromagnetic instability.
The solid solution between the ferromagnetic metal SrRuO$_3$ and the enhanced paramagnetic metal SrRhO$_3$ was recently reported [K. Yamaura et al., Phys. Rev. B 69 (2004) 024410], and an unexpected feature was found in the specific heat data at $x$=0.9 of SrRu$_{1-x}$Rh$_x$O$_3$. The feature was reinvestigated further by characterizing additional samples with various Ru concentrations in the vicinity of $x$=0.9. Specific heat and magnetic susceptibility data indicate that the feature reflects a peculiar magnetism of the doped perovskite, which appears only in the very narrow composition range 0.85$<$$x$$le$0.95.
Ambipolar transport is a commonly occurring theme in semimetals and semiconductors. Here we present an analytical formulation of the conductivity for a two-band system. Electron and hole carrier densities and their respective conductivities are mapped into a two-dimensional unit-less phase space. Provided that one of the carrier densities is known, the dimensionless phase space can be probed through magnetoresistance measurements. This formulation of the two-band model for conductivity is applied to magnetoresistance experiments on Ca$_3$Ru$_2$O$_7$. While previous such measurements focused on the low-temperature limit, we cover a broad temperature range and find negative magnetoresistance in an intermediate interval below the electronic transition at 48 K. The low-temperature magnetoresistance in Ca$_3$Ru$_2$O$_7$ is consistent with a two-band structure. However, the model fails to describe the full temperature and magnetic field dependence. Negative magnetoresistance found in an intermediate temperature range is, for example, not captured by this model. We thus conclude that the electronic and magnetic structure in this intermediate temperature range render the system beyond the most simple two-band model.
We study magnetic and multiferroic behavior in Ca$_3$Co$_{2-x}$Mn$_{x}$O$_6$ ($x sim$0.97) by high-field measurements of magnetization ($M$), magnetostriction ($L$($H$)/$L$), electric polarization ($P$), and magnetocaloric effect. This study also gives insight into the zero and low magnetic field magnetic structure and magnetoelectric coupling mechanisms. We measured $M$ and $Delta$$L$/$L$ up to pulsed magnetic fields of 92 T, and determined the saturation moment and field. On the controversial topic of the spin states of Co$^{2+}$ and Mn$^{4+}$ ions, we find evidence for $S$ = 3/2 spins for both ions with no magnetic field-induced spin-state crossovers. Our data also indicate that Mn$^{4+}$ spins are quasi-isotropic and develop components in the $ab$-plane in applied magnetic fields of 10 T. These spins cant until saturation at 85 T whereas the Ising Co$^{2+}$ spins saturate by 25 T. Furthermore, our results imply that mechanism for suppression of electric polarization with magnetic fields near 10 T is flopping of the Mn$^{4+}$ spins into the $ab$-plane, indicating that appropriate models must include the coexistence of Ising and quasi-isotropic spins.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
