اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدEntropy evolution in the magnetic phases of partially frustrated CePdAl
56
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
In the heavy-fermion metal CePdAl long-range antiferromagnetic order coexists with geometric frustration of one third of the Ce moments. At low temperatures the Kondo effect tends to screen the frustrated moments. We use magnetic fields $B$ to suppress the Kondo screening and study the magnetic phase diagram and the evolution of the entropy with $B$ employing thermodynamic probes. We estimate the frustration by introducing a definition of the frustration parameter based on the enhanced entropy, a fundamental feature of frustrated systems. In the field range where the Kondo screening is suppressed the liberated moments tend to maximize the magnetic entropy and strongly enhance the frustration. Based on our experiments, this field range may be a promising candidate to search for a quantum spin liquid.
قيم البحث
اقرأ أيضاً
We report on a single-crystal neutron diffraction study of the evolution of the antiferromagnetic order in the heavy-fermion compound CePd$_{1-x}$Ni$_x$Al which exhibits partial geometric frustration due to its distorted Kagome structure. The magneti
c structure is found to be unchanged with a propagation vector $Q_mathrm{AF} approx (0.5~0~0.35)$ for all Ni concentrations $x$ up to $x_c approx 0.14$. Upon approaching the quantum critical concentration $x_c$, the ordered moment vanishes linearly with Neel temperature $T_{rm N}$, in good agreement with CePdAl under hydrostatic pressure. For all Ni concentrations, substantial short-range magnetic correlations are observed above $T_{rm N}$ as a result of frustration.
Ba3Mn2O8 is a spin-dimer compound based on pairs of S=1, 3d^2, Mn^{5+} ions arranged on a triangular lattice. Antiferromagnetic intradimer exchange leads to a singlet ground state in zero-field. Here we present the first results of thermodynamic meas
urements for single crystals probing the high-field ordered states of this material associated with closing the spin gap to the excited triplet states. Specific heat, magnetocaloric effect, and torque magnetometry measurements were performed in magnetic fields up to 32 T and temperatures down to 20 mK. For fields above H_{c1} ~ 8.7 T, these measurements reveal a single magnetic phase for H parallel to c, but two distinct phases (approximately symmetric about the center of the phase diagram) for H perpendicular to c. Analysis of the simplest possible spin Hamiltonian describing this system yields candidates for these ordered states corresponding to a simple spiral structure for H parallel to c, and to two distinct modulated phases for H perpendicular to c. Both single-ion anisotropy and geometric frustration play crucial roles in defining the phase diagram.
We have investigated the crystal structure and magnetic properties for polycrystalline samples of LaMn1-xFexO3+y, in the whole range x=0.0 to x=1.0, prepared by solid state reaction in air. All samples show the ORT-2 orthorhombic structure that suppr
esses the Jahn-Teller distortion, thus favoring a ferromagnetic (FM) superexchange (SE) interaction between Mn^{3+}-O-Mn^{3+}. For x=0.0 the oxygen excess (y ~ 0.09) produces vacancies in the La and Mn sites and generates a fraction around 18% of Mn^{4+} ions and 82% of the usual Mn^{3+} ions, with possible double exchange interaction between them. The Fe doping in this system is known to produce only stable Fe^{3+} ions. We find an evolution from a fairly strong FM phase with a Curie temperature T_{C} ~ 160 K, for x=0.0, to an antiferromagnetic (AFM) phase with T_{N} = 790 K, for x=1.0, accompanied by clear signatures of a cluster-glass behavior. For intermediate Fe contents a mixed-phase state occurs, with a gradual decrease (increase) of the FM (AFM) phase, accompanied by a systematic transition broadening for 0.2 < x < 0.7. A model based on the expected exchange interaction among the various magnetic-ion types, accounts very well for the saturation-magnetization dependence on Fe doping.
The magnetic phases of a triangular-lattice antiferromagnet, CuCrO$_2$, were investigated in magnetic fields along to the $c$ axis, $H$ // [001], up to 120 T. Faraday rotation and magneto-absorption spectroscopy were used to unveil the rich physics o
f magnetic phases. An up-up-down (UUD) magnetic structure phase was observed around 90--105 T at temperatures around 10 K. Additional distinct anomalies adjacent to the UUD phase were uncovered and the Y-shaped and the V-shaped phases are proposed to be viable candidates. These ordered phases are emerged as a result of the interplay of geometrical spin frustration, single ion anisotropy and thermal fluctuations in an environment of extremely high magnetic fields.
Owing to the hybridization of ceriums localised 4$f$ electron and conduction band composed of $d$-electrons, cerium based intermetallics exhibit various kinds of magnetic interactions. In crystals, these can result in exotic types of magnetic orderin
g. In this study, we report a detailed single-crystal neutron diffraction study on CePdAl$_3$ and CePtAl$_3$. We have synthesized a large crystal of CePdAl$_3$, which crystallizes in a non-centrosymmetric, orthorhombic structure with space group $Cmc2_1$, a new, distorted variant of the tetragonal BaNiSn$_3$ structure observed in other Ce$T$Al$_3$ compounds, such as CePtAl$_3$. Low-temperature diffraction measurements showed that CePdAl$_3$ orders in a collinear antiferromagnetic structure below T$_N$=5.3 (1) K, with magnetic moments pointing along the $a$-axis direction and an ordered magnetic moment $mu$=1.64(3) $mu_B$/Ce$^{3+}$. Tetragonal CePtAl$_3$ shows a modulated, cycloidal type of ordering with $vec{k}=(frac{2}{3},0,0)$, and a transition temperature T$_N$=3.2 K. Symmetry analysis allows two types of ordering, which show modulation of both amplitude and direction of magnetic moments. These results allow to conclude that in Ce$T$Al$_3$ system the orthorhombic distortion ($T$=Pd, Ag) releases some underlying magnetic frustration that results in modulated types of magnetic ordering in tetragonal compounds ($T$=Cu,Au,Pt).
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
