اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدLiquid-like correlations in single crystalline Y2Mo2O7: an unconventional spin glass
258
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The spin glass behavior of Y2Mo2O7 has puzzled physicists for nearly three decades. Free of bulk disorder within the resolution of powder diffraction methods, it is thought that this material is a rare realization of a spin glass resulting from weak disorder such as bond disorder or local lattice distortions. Here, we report on the single crystal growth of Y2Mo2O7. Using neutron scattering, we present unique isotropic magnetic diffuse scattering arising beneath the spin glass transition despite having a well-ordered structure at the bulk level. Despite our attempts to model the diffuse scattering using a computationally exhaustive search of a class of simple spin Hamiltonians, we were unable to replicate the experimentally observed energy-integrated (diffuse) neutron scattering. A T^2-temperature dependence in the heat capacity and density functional theory calculations hint at significant frozen degeneracy in both the spin and orbital degrees of freedom resulting from spin-orbital coupling (Kugel-Khomskii type) and random fluctuations in the Mo environment at the local level.
قيم البحث
اقرأ أيضاً
We report on isothermal pulsed (20 ms) field magnetization, temperature dependent AC - susceptibility, and the static low magnetic field measurements carried out on 10 nm sized Pr0.5Ca0.5MnO3 nanoparticles (PCMO10). The saturation field for the magne
tization of PCMO10 (~ 250 kOe) is found to be reduced in comparison with that of bulk PCMO (~300 kOe). With increasing temperature, the critical magnetic field required to melt the residual charge-ordered phase decays exponentially while the field transition range broadens, which is indicative of a Martensite-like transition. The AC - susceptibility data indicate the presence of a frequency-dependent freezing temperature, satisfying the conventional Vogel-Fulcher and power laws, pointing to the existence of a spin-glass-like disordered magnetic phase. The present results lead to a better understanding of manganite physics and might prove helpful for practical applications.
A solid conducts heat through both transverse and longitudinal acoustic phonons, but a liquid employs only longitudinal vibrations. Here, we report that the crystalline solid AgCrSe2 has liquid-like thermal conduction. In this compound, Ag atoms exhi
bit a dynamic duality that they are exclusively involved in intense low-lying transverse acoustic phonons while they also undergo local fluctuations inherent in an order-to-disorder transition occurring at 450 K. As a consequence of this extreme disorder-phonon coupling, transverse acoustic phonons become damped as approaching the transition temperature, above which they are not defined anymore because their lifetime is shorter than the relaxation time of local fluctuations. Nevertheless, the damped longitudinal acoustic phonon survives for thermal transport. This microscopic insight might reshape the fundamental idea on thermal transport properties of matter and facilitates the optimization of thermoelectrics.
Spin glasses are a highly complex magnetic state of matter, intricately linked to spin frustration and structural disorder. They exhibit no long-range order and exude aging phenomena, distinguishing them from quantum spin liquids. We report a new typ
e of spin glass state, the spin-Q glass, observable in bulk-like crystalline metallic neodymium thick films. Using spin-polarized scanning tunneling microscopy combined with ab initio calculations and atomistic spin-dynamics simulations, we visualize the variations in atomic-scale non-collinear order and its response to magnetic field and temperature. We quantify the aging phenomena relating the glassiness to crystalline symmetry and the energy landscape. This result not only resolves the long-standing debate of the magnetism of neodymium, but also suggests that glassiness may arise in other magnetic solids lacking extrinsic disorder.
There has been growing interest in structural quantum phase transitions and quantum fluctuations of phonons in the research area of condensed matter physics. Here, we report the observation of glass-like features in the lattice heat capacity of a stu
ffed tridymite-type crystal, Ba1-xSrxAl2O4, a candidate compound of quantum paraelectrics. Substitutional chemical suppression of the ferroelectric phase transition temperature (TC) of Ba1-xSrxAl2O4 results in the disappearance of the TC at x=0.07. For the compositional window of x=0.2-0.5, the lattice heat capacity is enhanced below approximately 10 K and diverges from the T3-scaling law below 2.5 K. Synchrotron X-ray diffraction experiments on single crystals reveal the weakly correlated disorder in the crystal structure that survives down to low temperature; this disorder is responsible for the observed excess heat capacity. These features can be considered one of the manifestations of structural quantum fluctuations.
It is textbookly regarded that phonons, i.e., an energy quantum of propagating lattice waves, are the main heat carriers in perfect crystals. As a result, in many crystals, e.g., bulk silicon, the temperature-dependent thermal conductivity shows the
classical 1/T relationship because of the dominant Umklapp phonon-phonon scattering in the systems. However, the thermal conductivity of many crystalline metal-organic frameworks is very low and shows no, a weakly negative and even a weakly positive temperature dependence (glass-like thermal conductivity). It has been in debate whether the thermal transport can be still described by phonons in metal-organic frameworks. Here, by studying two typical systems, i.e., crystal zeolitic imidazolate framework-4 (cZIF-4) and crystal zeolitic imidazolate framework-62 (c-ZIF62), we prove that the ultralow thermal conductivity in metal-organic frameworks is resulting from the strong phonon intrinsic structure scattering due to the large mass difference and the large cavity between Zn and N atoms. Our mean free path spectrum analysis shows that both propagating and non-propagating anharmonic vibrational modes exist in the systems, and contribute largely to the thermal conductivity. The corresponding weakly negative or positive temperature dependence of the thermal conductivity is stemming from the competition between the propagating and non-propagating anharmonic vibrational modes. Our study here provides a fundamental understanding of thermal transport in metal-organic frameworks and will guide the design of the thermal-related applications using metal-organic frameworks, e.g., inflammable gas storage, chemical catalysis, solar thermal conversion and so on.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
