Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpecific-heat study for ferromagnetic and antiferromagnetic phases in SrRu_{1-x}Mn_xO3
289
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Low-temperature electronic states in SrRu_{1-x}Mn_xO_3 for x <= 0.6 have been investigated by means of specific-heat C_p measurements. We have found that a jump anomaly observed in C_p at the ferromagnetic (FM) transition temperature for SrRuO_3 changes into a broad peak by only 5% substitution of Mn for Ru. With further doping Mn, the low-temperature electronic specific-heat coefficient gamma is markedly reduced from the value at x=0 (33 mJ/K^2 mol), in connection with the suppression of the FM phase as well as the enhancement of the resistivity. For x >= 0.4, gamma approaches to ~ 5 mJ/K^2 mol or less, where the antiferromagnetic order with an insulating feature in resistivity is generated. We suggest from these results that both disorder and reconstruction of the electronic states induced by doping Mn are coupled with the magnetic ground states and transport properties.
rate research
Read More
Low-temperature specific heat of CaRu1-xMnxO3 was measured to clarify the role of d electrons in ferromagnetic and antiferromagnetic orders observed above x=0.2. Specific heat divided by temperature C_p/T is found to roughly follow a T^2 function, and relatively large magnitudes of electronic specific heat coefficient gamma were obtained in wide x range. In particular, gamma is unchanged from the value at x=0 (84 mJ/K^2 mol) in the paramagnetic state for x<=0.1, but linearly reduced with increasing x above x= 0.2. These features of gamma strongly suggest that itinerant d electrons are tightly coupled with the evolution of magnetic orders in small and intermediate Mn concentrations.
We have performed the powder neutron diffraction measurements on the solid solutions of SrRu_{1-x}Mn_xO_3, and found that the itinerant ferromagnetic order observed in pure SrRuO_3 changes into the C-type antiferromagnetic (AF) order with nearly localized d electrons in the intermediate Mn concentration between x=0.4 and 0.6. With increasing x, the AF moment is strongly enhanced from 1.1 mB (x=0.4) to 2.6 mB (x=0.6), which is accompanied by the elongation of the tetragonal c/a ratio. These results suggest that the substitution of Mn for Ru suppresses the itinerant character of the d electrons, and induces the superexchange interaction through the compression in the c plane. We have also found that the magnetic and transport properties observed in our tetragonal samples are quite similar to those of recently reported orthorhombic ones.
We present a complete characterization of ferromagnetic system CeIr2B2 using powder x-ray diffraction XRD, magnetic susceptibility chi(T), isothermal magnetization M(H), specific heat C(T), electrical resistivity rho(T,H), and thermoelectric power S(T) measurements. Furthermore 11B NMR study was performed to probe the magnetism on a microscopic scale. The chi(T), C(T) and rho(T) data confirm bulk ferromagnetic ordering with Tc = 5.1 K. Ce ions in CeIr2B2 are in stable trivalent state. Our low-temperature C(T) data measured down to 0.4 K yield Sommerfeld coefficient gamma = 73(4) mJ/molK2 which is much smaller than the previously reported value of gamma = 180 mJ/molK2 deduced from the specific heat measurement down to 2.5 K. For LaIr2B2 gamma = 6(1) mJ/molK2 which implies the density of states at the Fermi level D(EF) = 2.54 states/(eV f.u.) for both spin directions. The renormalization factor for quasi-particle density of states and hence for quasi-particle mass due to 4f correlations in CeIr2B2 is 12. The Kondo temperature TK ~ 4 K is estimated from the jump in specific heat of CeIr2B2 at Tc. Both C(T) and rho(T) data exhibit gapped-magnon behavior in magnetically ordered state with an energy gap Eg ~ 3.5 K. The rho data as a function of magnetic field H indicate a large negative magnetoresistance (MR) which is highest for T = 5 K.While at 5 K the negative MR keeps on increasing up to 10 T, at 2 K an upturn is observed near H = 3.5 T. On the other hand, the thermoelectric power data have small absolute values (S ~ 7 {mu}V/K) indicating a weak Kondo interaction. A shoulder in S(T) at about 30 K followed by a minimum at ~ 10 K is attributed to crystal electric field (CEF) effects and the onset of magnetic ordering. 11B NMR line broadening provides strong evidence of ferromagnetic correlations below 40 K.
We explore the magnetically-ordered ground state of the isovalently-substituted Mott-insulator Y$_{1-x}$La$_{x}$TiO$_{3}$ for $x$ $leq$ 0.3 via single crystal growth, magnetometry, neutron diffraction, x-ray magnetic circular dichroism (XMCD), muon spin rotation ($mu$SR) and small-angle neutron scattering (SANS). We find that the decrease in the magnetic transition temperature on approaching the ferromagnetic (FM) - antiferromagnetic (AFM) phase boundary at the La concentration $x_c$ $approx$ 0.3 is accompanied by a strong suppression of both bulk and local ordered magnetic moments, along with a volume-wise separation into magnetically-ordered and paramagnetic regions. The thermal phase transition does not show conventional second-order behavior, since neither a clear signature of dynamic critical behavior nor a power-law divergence of the magnetic correlation length is found for the studied substitution range; this finding becomes increasingly obvious with substitution. Finally, from SANS and magnetometry measurements, we discern a crossover from easy-axis to easy-plane magneto-crystalline anisotropy with increasing La substitution. These results indicate complex changes in magnetic structure upon approaching the phase boundary.
The specific heat and thermal conductivity of the insulating ferrimagnet Y$_3$Fe$_5$O$_{12}$ (Yttrium Iron Garnet, YIG) single crystal were measured down to 50 mK. The ferromagnetic magnon specific heat $C$$_m$ shows a characteristic $T^{1.5}$ dependence down to 0.77 K. Below 0.77 K, a downward deviation is observed, which is attributed to the magnetic dipole-dipole interaction with typical magnitude of 10$^{-4}$ eV. The ferromagnetic magnon thermal conductivity $kappa_m$ does not show the characteristic $T^2$ dependence below 0.8 K. To fit the $kappa_m$ data, both magnetic defect scattering effect and dipole-dipole interaction are taken into account. These results complete our understanding of the thermodynamic and thermal transport properties of the low-lying ferromagnetic magnons.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
