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Register a new userCoexisting magnetic structures and spin-reorientation in Er$_{0.5}$Dy$_{0.5}$FeO$_{3}$: Bulk magnetization, neutron scattering, specific heat, and emph{Ab-initio} studies
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The complex magnetic structures, spin-reorientation and correlated exchange interactions have been investigate in Er$_{0.5}$Dy$_{0.5}$FeO$_3$ using bulk magnetization, neutron diffraction, specific heat measurements and density functional theory calculations. The Fe$^{3+}$ spins order as G-type antiferromagnet structure depicted by ${Gamma}_{4}$($G_{x}$,$A_{y}$,$F_{z}$) irreducible representation below 700K, similar to its end compounds. The bulk magnetization data indicate occurrence of the spin-reorientation and rare-earth magnetic ordering below $sim$75 K and 10 K, respectively. The neutron diffraction studies confirm an incomplete ${Gamma}_{4}$${rightarrow}$ ${Gamma}_{2}$($F_{x}$,$C_{y}$,$G_{z}$) spin-reorientation initiated $leq$75 K. Although, the relative volume fraction of the two magnetic structures varies with decreasing temperature, both co-exist even at 1.5 K. At 8 K, Er$^{3+}$/Dy$^{3+}$ moments order as $c_{y}^R$ arrangement develop, which gradually increases in intensity with decreasing temperature. At 2 K, magnetic structure associated with $c_{z}^R$ arrangement of Er$^{3+}$/Dy$^{3+}$ moments also appears. At 1.5 K the magnetic structure of Fe$^{3+}$ spins is represented by a combination of ${Gamma}_{2}$+${Gamma}_{4}$+${Gamma}_{1}$, while the rare earth moments coexists as $c_{y}^R$ and $c_{z}^R$ corresponding to ${Gamma}_{2}$ and ${Gamma}_{1}$ representation, respectively. The observed Schottky anomaly at 2.5 K suggests that the rare-earth ordering is induced by polarization due to Fe$^{3+}$ spins. The Er$^{3+}$-Fe$^{3+}$ and Er$^{3+}$-Dy$^{3+}$ exchange interactions, obtained from first principle calculations, primarily cause the complicated spin-reorientation and $c_{y}^R$ rare-earth ordering, respectively, while the dipolar interactions between rare-earth moments, result in the $c_{z}^R$ type rare-earth ordering at 2 K.
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The structural, magnetic, and electronic properties of NdFe$_{0.5}$Mn$_{0.5}$O$_3$ have been studied in detail using bulk magnetization, neutron/x-ray diffraction and first principles density functional theory calculations. The material crystallizes in the orthorhombic $Pbnm$ structure, where both Mn and Fe occupy the same crystallographic site ($4b$). Mn/Fe sublattice of the compound orders in to a G-type antiferromagnetic phase close to 250,K where the magnetic structure belongs to ${Gamma}_{1}$ irreducible representation with spins aligned along the crystallographic $b$ direction. This is unconventional in the sense that most of the orthoferrites and orthochromites order in the ${Gamma}_{4}$ representation below the N{e}el temperature.This magnetic structure then undergoes a complete spin reorientation transition with temperature in the range 75,K$gtrsim$ T $gtrsim$ 25,K where the magnetic structure exists as a sum of two irreducible representations (${Gamma}_{1}$+${Gamma}_{2}$) as seen from neutron diffraction measurements. At 6,K, the magnetic structure belongs entirely to ${Gamma}_{2}$ representation with spins aligned antiferromagnetically along the crystallographic $c$ direction having a small ferromagnetic component ($F_x$). The unusual spin reorientation and correlation between magnetic ground state and electronic structure have been investigated using first principles calculations within GGA+U and GGA+U+SO formalisms.
In present study, the magnetic structure and spin reorientation of mixed doped orthoferrite Nd$_{0.5}$Dy$_{0.5}$FeO$_3$ have been investigated. Similar to both parent compounds (NdFeO$_3$ and DyFeO$_3$), the magnetic structure of Fe$^{3+}$ belongs to ${Gamma}_{4}$ irreducible representation (G$_{x}$, F$_{z}$) at room temperature. The experimental measurements confirmed the spin reorientation where magnetic structure of Fe$^{3+}$ changes from ${Gamma}_{4}$ to ${Gamma}_{2}$(F$_{x}$, G$_{z}$) between 75 and 20 ,K while maintaining G-type configuration. Such a gradual spin reorientation is unusual since the large single ion anisotropy of Dy$^{3+}$ ions causes an abrupt ${Gamma}_{4}$${rightarrow}$ ${Gamma}_{1}$(G$_{y}$) spin reorientation in DyFeO$_3$. Between 20 and 10 ,K, the Fe$^{3+}$ magnetic structure is represented by ${Gamma}_{2}$ (F$_{x}$, G$_{z}$). Unexpectedly, magnetic structure of Fe$^{3+}$ with ${Gamma}_{4}$ representation re-emerges below 10,K which also coincides with the development of rare-earth (Nd$^{3+}$/Dy$^{3+}$) magnetic ordering having C$_{y}$ configuration with magnetic moment of 1.8 ${mu}_{B}$. The absence of any signature of second order phase transition in the specific heat confirms the role of $R$(Nd$^{3+}$/Dy$^{3+}$)-Fe$^{3+}$ exchange interaction in the observed rare-earth ordering unlike DyFeO$_3$ where Dy$^{3+}$ ordering takes place independently to the magnetic ordering of Fe$^{3+}$ magnetic structure. Our (DFT+U+SO) calculations show that the C-type arrangement of rare-earth ions (Nd$^{3+}$/Dy$^{3+}$) with ${Gamma}_{2}$ configuration for Fe$^{3+}$ moments is the ground state whereas ${Gamma}_{4}$ phase is energetically very close. Nd-Fe and Nd-Dy exchange interactions, estimated from DFT, are observed to have significant roles in the rare earth ordering and Fe spin reorientation corroborating our experimental results.
Recent progress in the field of multiferroics led to the discovery of many new materials in which ferroelectricity is induced by cycloidal spiral orders. The direction of the electric polarization is typically constrained by spin anisotropies and magnetic field. Here, we report that the mixed rare-earth manganite, Gd$_{0.5}$Dy$_{0.5}$MnO$_3$, exhibits a spontaneous electric polarization along a general direction in the crystallographic ac-plane, which is suppressed below 10 K but re-emerges in an applied magnetic field. Neutron diffraction measurements show that the polarization direction results from a large tilt of the spiral plane with respect to the crystallographic axes and that the suppression of ferroelectricity is caused by the transformation of a cycloidal spiral into a helical one, a unique property of this rare-earth manganite. The freedom in the orientation of the spiral plane allows for a fine magnetic control of ferroelectricity, i.e. a rotation as well as a strong enhancement of the polarization depending on the magnetic field direction. We show that this unusual behavior originates from the coupling between the transition metal and rare-earth magnetic subsystems.
Orthorhombic single crystals of TbMn0.5Fe0.5O3 are found to exhibit spin-reorientation, magnetization reversal and weak ferromagnetism. Strong anisotropy effects are evident in the temperature dependent magnetization measurements along the three crystallographic axes a, b and c. A broad magnetic transition is visible at T_N (Fe/Mn) = 286 K due to paramagnetic to AxGyCz ordering. A sharp transition is observed at T_SR (Fe/Mn) = 28 K, which is pronounced along c axis in the form of a sharp jump in magnetization where the spins reorient to GxAyFz configuration. The negative magnetization observed below TSR Fe/Mn along c axis is explained in terms of domain wall pinning. A component of weak ferromagnetism is observed in field-scans along c-axis but below 28 K. Field-induced steps-like transitions are observed in hysteresis measurement along b axis below 28 K. It is noted that no sign of Tb-order is discernible down to 2 K. TbMn0.5Fe0.5O3 could be highlighted as a potential candidate to evaluate its magneto-dielectric effects across the magnetic transitions.
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.
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