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Register a new userSpin-Reorientation and Weak Ferromagnetism in Antiferromagnetic TbMn_{0.5}Fe_{0.5}O_3
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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.
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The perovskite TbFe$_{0.5}$Cr$_{0.5}$O$_3$ shows two anomalies in the magnetic susceptibility at $T_N$ = 257K and $T_{SR}$ = 190K which are respectively, the antiferromagnetic and spin reorientation transition that occur in the Fe/Cr sublattice. Analysis of the magnetic susceptibility reveals signatures of Griffiths-like phase in this compound. Neutron diffraction analysis confirms that, as the temperature is reduced from 350K, a spin reorientation transition from $Gamma_2$ (F$_x$, C$_y$, G$_z$) to $Gamma_4$ (G$_x$, A$_y$, F$_z$) occurs at $T_N$ = 257K and subsequently, a second spin reorientation takes place from $Gamma_4$ (G$_x$, A$_y$, F$_z$) to $Gamma_2$ (F$_x$, C$_y$, G$_z$) at $T_{SR}$ = 190K. The $Gamma_2$ (F$_x$, C$_y$, G$_z$) structure is stable until 7.7K where an ordered moment of 7.74(1)$mu_mathrm B$/Fe$^{3+}$(Cr$^{3+}$) is obtained from neutron data refinement. In addition to the long-range order of the magnetic structure, indication of diffuse magnetic scattering at 7.7K is evident, thereby lending support to the Griffiths-like phase observed in susceptibility. At 7.7K, Tb develops a ferromagnetic component along the crystallographic $a$ axis. Thermal conductivity, and spin-phonon coupling of TbFe$_{0.5}$Cr$_{0.5}$O$_3$ through Raman spectroscopy are studied in the present work. An antiferromagnetic structure with ($uparrow downarrow uparrow downarrow$) arrangement of Fe/Cr spins is found in the ground state through first-principles energy calculations which supports the experimental magnetic structure at 7.7K. The spin-resolved total and partial density of states are determined showing that TbFe$_{0.5}$Cr$_{0.5}$O$_3$ is insulating with a band gap of $sim 0.12$ (2.4) eV within GGA (GGA+$U$) functionals.
Using ab initio calculations and special quasirandom structures, we have characterized the distribution of defect formation energy and migration barrier in Ni-based solid-solution alloys: Ni_{0.5}Co_{0.5}, Ni_{0.5}Fe_{0.5}, Ni_{0.8}Fe_{0.2} and Ni_{0.8}Cr_{0.2}. As defect formation energies depend sensitively on elemental chemical potential, we have developed a computationally efficient method for determining it which takes into account the global composition and local short-range order. We find that Fe has the biggest alloy effects for Ni among these four elements. Our results show that the distribution of migration energies for vacancies and interstitial have a region of overlap, which will facilitate the recombination between them.
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.
We report the structural, static, and dynamic properties of Cr$_{0.5}$Fe$_{0.5}$Ga by means of powder x-ray diffraction, magnetization, heat capacity, magnetic relaxation, and magnetic memory effect measurements. DC magnetization and AC susceptibility studies reveal a spin-glass transition at around $T_{rm f} simeq 22$~K. An intermediate value of the relative shift in freezing temperature $delta T_{rm f} simeq 0.017$, obtained from the AC susceptibility data reflects the formation of cluster spin-glass states. The frequency dependence of $T_{rm f}$ is also analyzed within the framework of dynamic scaling laws. The analysis using power law yields a time constant for a single spin flip $tau* simeq 1.1times10^{-10}$~s and critical exponent $z u^{prime}=4.2pm0.2$. On the other hand, the Vogel-Fulcher (VF) law yields the time constant for a single spin flip $tau_0 simeq 6.6times10^{-9}$~s, VF temperature $T_{rm 0}=21.1pm0.1$~K, and an activation energy $E_{rm a}/k_{rm B} simeq 16$~K. The value of $tau*$ and $tau_0$ along with a non-zero value of $T_{rm 0}$ provide further evidence for the cluster spin-glass behaviour. The magnetic field dependent $T_{rm f}$ follows the de Almeida-Thouless line with a non-mean-field type instability, reflecting either a different universality class or strong anisotropy in the spin system. A detailed non-equilibrium dynamics study via relaxation and memory effect experiments demonstrates striking memory effects. All the above observations render a cluster spin-glass behaviour which is triggered by magnetic frustration due to competing antiferromagnetic and ferromagnetic interactions and magnetic site disorder. Moreover, the asymmetric response of magnetic relaxation with respect to the change in temperature, below $T_{rm f}$ can be explained by the hierarchical model.
Magnetization and neutron diffraction measurements indicate long-range antiferromagnetic ordering below TN=4 K in the 2D, S=1/2 Heisenberg antiferromagnet K2V3O8. The ordered state exhibits ``weak ferromagnetism and novel, field-induced spin reorientations. These experimental observations are well described by a classical, two-spin Heisenberg model incorporating Dzyaloshinskii-Moriya interactions and an additional c-axis anisotropy. This additional anisotropy can be accounted for by inclusion of the symmetric anisotropy term recently described by Kaplan, Shekhtman, Entin-Wohlman, and Aharony. This suggests that K2V3O8 may be a very unique system where the qualitative behavior relies on the presence of this symmetric anisotropy.
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