Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCluster spin-glass behaviour and memory effect in Cr$_{0.5}$Fe$_{0.5}$Ga
229
0
0.0
(
0
)
Added by
Ramesh Chandra Nath
Publication date
2018
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
We have studied a non volatile memory effect in the mixed valent compound La$_{0.5}$Ca$_{0.5}$MnO$_{3}$ induced by magnetic field (H). In a previous work [R.S. Freitas et al., Phys. Rev. B 65 (2002) 104403], it has been shown that the response of this system upon application of H strongly depends on the temperature range, related to three well differentiated regimes of phase separation occurring below 220 K. In this work we compare memory capabilities of the compound, determined following two different experimental procedures for applying H, namely zero field cooling and field cooling the sample. These results are analyzed and discussed within the scenario of phase separation.
We have studied the critical behaviour in $La_{0.5}Sr_{0.5}CoO_{3}$ near the paramagnetic-ferromagnetic transition temperature. We have analysed our dc magnetisation data near the transition temperature with the help of modified Arrott plots, Kouvel-Fisher method. We have determined the critical temperature $T_c$ and the critical exponents, $beta$ and $gamma$. With these values of $T_c$, $beta$ and $gamma$, we plot $M/(1-T/T_c)^{beta}$ vs $H/(1-T/T_c)^{gamma}$. All the data collapse on one of the two curves. This suggests that the data below and above $T_c$ obeys scaling, following a single equation of state.
Pb(Fe$_{0.5}$Nb$_{0.5}$)O$_3$ (PFN), one of the few relaxor multiferroic systems, has a $G$-type antiferromagnetic transition at $T_N$ = 143 K and a ferroelectric transition at $T_C$ = 385 K. By using high-resolution neutron-diffraction experiments and a total scattering technique, we paint a comprehensive picture of the long- and short-range structures of PFN: (i) a clear sign of short-range structural correlation above $T_C$, (ii) no sign of the negative thermal expansion behavior reported in a previous study, and (iii) clearest evidence thus far of magnetoelectric coupling below $T_N$. We conclude that at the heart of the unusual relaxor multiferroic behavior lies the disorder between Fe$^{3+}$ and Nb$^{5+}$ atoms. We argue that this disorder gives rise to short-range structural correlations arising from O disorder in addition to Pb displacement.
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.
La$_{1.5}$Sr$_{0.5}$CoMn$_{0.5}$Fe$_{0.5}$O$_{6}$ (LSCMFO) compound was prepared by solid state reaction and its structural, electronic and magnetic properties were investigated. The material forms in rhombohedral $Rbar{3}c$ structure, and the presence of distinct magnetic interactions leads to the formation of a Griffiths phase above its FM transition temperature (150 K), possibly related to the nucleation of small short-ranged ferromagnetic clusters. At low temperatures, a spin glass-like phase emerges and the system exhibits both the conventional and the spontaneous exchange bias (EB) effects. These results resemble those reported for La$_{1.5}$Sr$_{0.5}$CoMnO$_{6}$ but are discrepant to those found when Fe partially substitutes Co in La$_{1.5}$Sr$_{0.5}$(Co$_{1-x}$Fe$_{x}$)MnO$_{6}$, for which the EB effect is observed in a much broader temperature range. The unidirectional anisotropy observed for LSCMFO is discussed and compared with those of resembling double-perovskite compounds, being plausibly explained in terms of its structural and electronic properties.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
