ترغب بنشر مسار تعليمي؟ اضغط هنا

Evaluating the Effects of Structural Disorder on the Magnetic Properties of Nd$_{2}$Zr$_{2}$O$_{7}$

89   0   0.0 ( 0 )
 نشر من قبل Eli Zoghlin
 تاريخ النشر 2021
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

Motivated by the variation in reported lattice parameters of floating-zone-grown Nd$_{2}$Zr$_{2}$O$_{7}$ crystals, we have performed a detailed study of the relationship between synthesis environment, structural disorder, and magnetic properties. Using a combination of polycrystalline standards, electron-probe microanalysis and scattering techniques, we show that crystals grown under atmospheric conditions have a reduced lattice parameter - relative to pristine polycrystalline powders - due to occupation of the Nd-site by excess Zr (i.e. negative stuffing). In contrast, crystals grown under high-pressure Ar are nearly stoichiometric with an average lattice parameter approaching the polycrystalline value. While minimal disorder of the oxygen sublattices is observed on the scale of the average structure, neutron pair-distribution function analysis indicates a highly local disorder of the oxygen coordination, which is only weakly dependent on growth environment. Most importantly, our magnetization, heat capacity and single-crystal neutron scattering data show that the magnetic properties of crystals grown under high-pressure Ar match closely with those of stoichiometric powders. Neutron scattering measurements reveal that the signature of magnetic moment fragmentation - the coexistence of all-in-all-out (AIAO) magnetic Bragg peaks and diffuse pinch-point scattering due to spin-ice correlations - persists in these nearly stoichiometric crystals. However, in addition to an increased AIAO transition temperature, the diffuse signal is seemingly stabilized and remains nearly unchanged upon warming to 800 mK. This behavior indicates that both the AIAO magnetic order and spin-ice correlations are sensitive to deviations of the Nd stoichiometry.



قيم البحث

اقرأ أيضاً

Searching for an ideal Kitaev spin liquid candidate with anyonic excitations and long-range entanglement has motivated the synthesis of a new family of intercalated Kitaev magnets such as H$_{3}$LiIr$_{2}$O$_{6}$, Cu$_{2}$IrO$_{3}$, and Ag$_{3}$LiIr$ _{2}$O$_{6}$. The absence of a susceptibility peak and a two-step release of the magnetic entropy in these materials has been proposed as evidence of proximity to the Kitaev spin liquid. Here we present a comparative study of the magnetic susceptibility, heat capacity, and muon spin relaxation ($mu$SR) between two samples of Ag$_{3}$LiIr$_{2}$O$_{6}$ in the clean and disordered limits. In the disordered limit, the absence of a peak in either susceptibility or heat capacity and a weakly depolarizing $mu$SR signal may suggest a proximate spin liquid ground state. In the clean limit, however, we resolve a peak in both susceptibility and heat capacity data, and observe clear oscillations in $mu$SR that confirm long-range antiferromagnetic ordering. The $mu$SR oscillations fit to a Bessel function, characteristic of an incommensurate order, as reported in the parent compound $alpha$-Li$_{2}$IrO$_{3}$. Our results clarify the role of structural disorder in the intercalated Kitaev magnets.
80 - J. Xu , Owen Benton , V. K. Anand 2019
We present thermodynamic and neutron scattering measurements on the quantum spin ice candidate Nd$_2$Zr$_2$O$_7$. The parameterization of the anisotropic exchange Hamiltonian is refined based on high-energy-resolution inelastic neutron scattering dat a together with thermodynamic data using linear spin wave theory and numerical linked cluster expansion. Magnetic phase diagrams are calculated using classical Monte Carlo simulations with fields along mbox{[100]}, mbox{[110]} and mbox{[111]} crystallographic directions which agree qualitatively with the experiment. Large hysteresis and irreversibility for mbox{[111]} is reproduced and the microscopic mechanism is revealed by mean field calculations to be the existence of metastable states and domain inversion. Our results shed light on the explanations of the recently observed dynamical kagome ice in Nd$_2$Zr$_2$O$_7$ in mbox{[111]} fields.
The delicate balance between spin-orbit coupling, Coulomb repulsion and crystalline electric field interactions observed in Ir-based oxides is usually manifested as exotic magnetic behavior. Here we investigate the evolution of the exchange coupling between Co and Ir for partial La substitution by Ca in La$_{2}$CoIrO$_6$. A great advantage of the use of Ca$^{2+}$ as replacement for La$^{3+}$ is the similarity of its ionic radii. Thus, the observed magnetic changes can more easily be associated to electronic variations. A thorough investigation of the structural, electronic and magnetic properties of the La$_{2-x}$Ca$_{x}$CoIrO$_6$ system was carried out by means of synchrotron x-ray powder diffraction, muon spin rotation and relaxation ($mu$SR), AC and DC magnetization, XAS, XMCD, Raman spectroscopy, electrical resistivity and dielectric permittivity. Our XAS results show that up to 25% of Ca substitution at the La site results in the emergence of Co$^{3+}$, possibly in high spin state, while the introduction of larger amount of Ca leads to the increase of Ir valence. The competing magnetic interactions resulting from the mixed valences lead to a coexistence of a magnetically ordered and an emerging spin glass (SG) state for the doped samples. Our $mu$SR results indicate that for La$_{2}$CoIrO$_6$ a nearly constant fraction of a paramagnetic (PM) phase persists down to low temperature, possibly related to the presence of a small amount of Ir$^{3+}$ and to the anti-site disorder at Co/Ir sites. For the doped compounds the PM phase freezes below 30 K, but there is still some dynamics associated with the SG. The dielectric data obtained for the parent compound and the one with 25% of Ca-doping indicate a possible magnetodielectric effect, which is discussed in terms of the electron hopping between the TM ions, the anti-site disorder and the distorted crystalline structure.
We present the results of structural and magnetic phase comparisons of the iron oxychalcogenides La$_{2}$O$_{2}$Fe$_{2}$O$M$$_{2}$ ($M$ = S, Se). Elastic neutron scattering reveals that $M$ = S and Se have similar nuclear structures at room and low t emperatures. We find that both materials obtain antiferromagnetic ordering at a Neel temperature $T_{N}$ 90.1 $pm$ 0.16 K and 107.2 $pm$ 0.06 K for $M$= Se and S, respectively. The magnetic arrangements of $M$ = S, Se are obtained through Rietveld refinement. We find the order parameter exponent $beta$ to be 0.129 $pm$ 0.006 for $M$ = Se and 0.133 $pm$ 0.007 for $M$ = S. Each of these values is near the Ising symmetry value of 1/8. This suggests that although lattice and electronic structural modifications result from chalcogen exchange, the nature of the magnetic interactions is similar in these materials.
Here, we report the growth and characterization of single crystals of NdxSb2-xTe3, by solid state reaction route via self-flux method. The phase and layered growth are confirmed through x-ray diffraction and Scanning electron microscopy respectively. A slight contraction in lattice parameters is seen after Nd doping. Also a minute shift in vibrational modes of recorded Raman spectra has been observed by doping of Nd in Sb2Te3. The magneto-resistance values under magnetic field of 5Tesla for Sb2Te3 are 75 percent at 2.5K and 60 percent at 20K, but only 40 percent at 5K for Nd0.1Sb1.9Te3. DC magnetic measurements exhibit expected diamagnetic and paramagnetic behaviors for pure and Nd doped crystals respectively. A cusp-like behavior is observed in magneto conductivity of both pure and Nd doped crystals at low magnetic fields below 1 Tesla which is analyzed using Hikami Larkin Nagaoka (HLN) model. For Sb2Te3 the fitted parameters alpha values are -1.02 and -0.58 and the phase coherence lengths are 50.8(6)nm & 34.9(8)nm at temperatures 2.5K and 20K respectively. For Nd0.1Sb1.9Te3, alpha is -0.29 and coherence length is 27.2(1) nm at 5K. The {alpha} values clearly show the presence of weak anti localization effect in both, pure and Nd doped samples. Also with Nd doping, the contribution of bulk states increases in addition to conducting surface states in overall conduction mechanism.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا