Aya Tobo

Characteristic magnetic structure due to antiferroquadrupolar ordering in Ho11B2C2

We determined the magnetic structures of the antiferroquadrupolar (AFQ) ordering material with a tetragonal crystal structure, Ho 11 B 2 C 2 , by neutron diffraction technique. The ground state of ...

Anomalous Antiferromagnetic Properties of the Tetragonal Compound, TbB2C2

Magnetic properties of the tetragonal compound TbB 2 C 2 were investigated by means of specific heat, magnetization and neutron diffraction measurements. TbB 2 C 2 is an antiferromagnet with T N = ...

Magnetic Order-Order Transition in Tetragonal ErB2C2.

We have investigated magnetic properties of ErB 2 C 2 which is an isostructural compound of the antiferroquadrupolar ordering materials, DyB 2 C 2 and HoB 2 C 2 , by magnetisation and neutron diffraction measurements. ErB 2 C 2 shows magnetic transitions at T N = 15.9 K and T t = 13.0 K. The magnetic structure of the ground state is a simple Ising-type antiferromagnetic one with a propagation vector of k =(1, 0, 0). The intermediate phase between T N and T t under zero magnetic field is a long range magnetic ordered state with a transverse sinusoidal modulation with a propagation vector of (1+δ, δ, 0), where δ=0.1120(2) which is nearly the same as that in phase IV in HoB 2 C 2 .

Systematic Study on Crystal Structures in Tetragonal RB2C2 (R=Rare Earth) Compounds

Detailed crystal structures of the tetragonal RB 2 C 2 (R=La, Ce, Pr, Nd, Tb, Dy, Ho, Er, Tm and Lu) compounds which include the antiferroquadrupolar ordering materials, DyB 2 C 2 and HoB 2 C 2 , h...

Effects of Y dilution on the antiferroquadrupolar ordering in the tetragonal compound DyB2C2

Antiferroquadrupolar (AFQ) and magnetic transitions in Dy 1- x Y x B 2 C 2 (0≤ x ≤0.6) have been investigated on the single-crystalline samples by magnetization and specific heat measurements. As the Y concentration increases, the magnetic transition temperature decreases from 15.3 K at x =0 to 4.5 K at x =0.6. The AFQ transition temperature also decreases from 24.7 K at x =0 to 7.4 K at x =0.6, although it becomes unclear for x ≥0.5 in the magnetization. A λ-type peak of specific heat at T Q becomes broader as x increases, and changess to a small upheaval for x ≥0.5. On the other hand, the field-induced transitions at the boundary between the AFQ and paramagnetic phases are clearly observed in the magnetization processes at 1.5 K x ≤0.6. The behavior of specific heat implies that the AFQ interaction acts strongly in a rather shorter distance than the antiferromagnetic interaction in DyB 2 C 2 . The Y dilution causes in a wide distribution of the AFQ interaction strength acting on the Dy quadrupoles. Then...

Lattice Constants, Electrical Resistivity and Specific Heat of RNiC2

Anomalous temperature dependence of electrical resistivity was found to be ubiquitous among the compounds RNiC 2 with R = La, Ce, Nd, Sm, Gd, Tb and Er. Lattice parameters were also observed to exhibit anomalous temperature dependence for some of the compounds studied by X-ray diffraction. It is argued that the existence of charge modulated structures is the cause of the former anomalies. The latter anomalies, on the other hand, are likely to be related to the coupling between the lattice and the f-electrons. Results of heat capacity measurements are used to estimate crystal field levels in NdNiC 2 and SmNiC 2 .

Antiferroquadrupolar Ordering in the Pseudo-Binary Tetragonal Compounds Ho1-xDyxB2C2

Antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) transitions in Ho 1- x Dy x B 2 C 2 (0 ≤ x ≤1.0) have been investigated on the single-crystalline samples by magnetization and specific heat measurements. As the Dy concentration increases, the both transition temperatures increases from T Q =4.5 K and T N =5.9 K for x =0 to T Q =24.7 K and T N =15.3 K for x =1. For x =0.2 and 0.3, there appears a single transition at which the AFQ and AFM transitions occur simultaneously. For 0.4 ≤ x , the two transition temperatures are reversed. The temperature dependence of specific heat is interpreted well by assuming that the entropy of R ln 3 is released through the successive transitions in HoB 2 C 2 , that is, the 4 f ground state of Ho 3+ ion is a quasi-triplet. It is supposed that the Ho 3+ ion has a rather small quadrupolar moment compared with the Dy 3+ quadrupole.

Antiferromagnetic order above antiferroquadrupolar transition temperature of HoB2C2

Abstract We have performed neutron diffraction measurements on a single crystal sample of tetragonal Ho11B2C2, which shows an antiferromagnetic order above an antiferroquadrupolar transition temperature. The magnetic structure of the intermediate phase, phase IV, has a long periodicity, and the order is short ranged. It is represented with a propagation vector k=[1+δ δ δ′] , where δ∼0.11 and δ′∼0.04.

Magnetic Property and Phase Diagram of the Diluted Antiferromagnet MnxMg1-xTiO3.

In order to investigate the mechanism of the occurrence of a spin-glass freezing in diluted antiferromagnets, we have measured the temperature variation of the low-field dc-magnetizations for the single crystal samples of the diluted antiferromagnet Mn x Mg 1- x TiO 3 (0.50≤ x ≤0.96). We also performed ac-susceptibility measurements and neutron scattering measurements. We have found that the samples with 0.62≤ x ≤0.96 establish antiferromagnetic long-range order at low temperatures, the sample with x =0.60 behaves like a reentrant-spin-glass system, and the samples with 0.50≤ x ≤0.56 behave like a spin-glass system. From these results, we construct the magnetic phase diagram of Mn x Mg 1- x TiO 3 in the concentration-temperature plane. The origin of the spin-glass behavior and reentrant-spin-glass behavior is discussed in relation to the percolation concentration of diluted magnetic systems.

Magnetic Phase Diagrams of Antiferroquadrupolar Ordering Compound DyB2C2

Specific heat and magnetization measurements were performed precisely on the antiferroquadruplar (AFQ) ordering compound DyB 2 C 2 in order to reexamine its magnetic B – T phase diagrams. We find new phase boundaries in both diagrams with B ∥[1 0 0] and B ∥[1 1 0], and revise the field dependency of some boundaries. In the resultant diagrams, all the phase have closed regions in the B – T space. Two phase boundaries start from T N in both diagrams with B ∥[1 0 0] and B ∥[1 1 0]. The one decreases its transition temperature with increasing field which is the same behavior just to normal antiferromagnets. The other gradually increases its transition temperature with increasing fields, which seems to satisfy behavior demanded for magnets with spontaneous magnetizations. The new-found boundary divides the previously reported AFQ phase into two phases. The one has magnetically ordered moments on the AFQ ordered quadrupoles and exists only in magnetic fields. The other is a pure AFQ phase with paramagnetic mome...