Kentaro Indoh

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...

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...

Quadrupolar and Magnetic Interactions in Antiferroquadrupolar Ordering Compound DyB2C2 Studied by Y Dilution

In order to elucidate quadrupolar and magnetic interactions in the antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) ordering compound DyB 2 C 2 , neutron diffraction experiments were performed on powdered and single-crystalline samples in addition to reexamination of specific heat and magnetization properties on the Y-diluted system Dy 1- x Y x B 2 C 2 . The results suggest that there is a percolation threshold at x =0.4–0.5 for the AFQ ordering. The broadening behavior of magnetic reflection peaks by the Y dilution suggests that the AFQ interaction is probably pseudo-one-dimensional with strong AFQ interactions along the c -axis and weak ferroquadrupolar interactions in the c -plane.

Detailed Measurements of Characteristic Profiles of Magnetic Diffuse Scattering in ErB2C2

Detailed neutron diffraction measurements were performed on a single crystalline sample of Er 11 B 2 C 2 . We observed magnetic diffuse scattering, which consists of three components, just above the transition temperatures. This scattering is also observed in anomalous antiferroquadrupolar ordering compounds,TbB 2 C 2 and HoB 2 C 2 . The results of the experiments indicate that the antiferroquadrupolar interaction is not essential for the origin of the magnetic diffuse scattering.

Neutron scattering study on the antiferroquadrupolar order of DyB2C2 under magnetic fields

Antiferroquadrupolar (AFQ) ordering in DyB2C2 has been investigated by means of neutron scattering under applied magnetic fields along [110] up to 10 T. In the AFQ ordered phase at 16 K, antiferromagnetic reflections indexed as 001/2 and 111/2 are induced by a magnetic field of 1 T. These induced magnetic reflections disappear at 2 T, and develop again, increasing in intensity with increasing field, above 3 T. As temperature increases, the integrated intensity at 4 T shows an anomalous decrease toward ~13 K in addition to a disappearance at TQ, while that at 8 T decreases normally toward TQ. We observed this curious behaviour of the induced magnetic reflections within the AFQ ordered phase.

Magnetic phase diagrams of Dy0.8Gd0.2B2C2

Gd substitution in DyB2C2, which undergoes an antiferroquadrupolar (AFQ) ordering at TQ = 24.7 K and an antiferromagnetic (AFM) one at TN = 15.3 K, enhances the AFM interaction and weakens the AFQ interaction, and the transition sequence at 20% Gd is the reverse of that in DyB2C2. The AFQ transition occurs at TQ = 17.5 K, below the AFM one at TN = 19.0 K in Dy0.8Gd0.2B2C2. The present work provides some experimental results on the specific heat and magnetization of Dy0.8Gd0.2B2C2. The magnetic phase diagrams of Dy0.8Gd0.2B2C2 have some resemblance to those of HoB2C2 and Ce0.75La0.25B6. There is an anomalous magnetic phase (named phase IV) that is adjacent to the AFQ phase in each compound.

Anomalous magnetic scattering in tetragonal RB2C2 (R = rare earth) observed by means of neutron diffraction

Detailed neutron diffraction experiments have been performed on tetragonal R11B 2C2 (R = rare-earth) compounds which show characteristic antiferroquadrupolar orderings. TbB2C2, ErB2C2 and HoB2C2, which have magnetic long-periodic states, show anomalous magnetic diffuse scattering with flat intensity. The anomalous diffuse scattering exists in a small region in the reciprocal space, surrounded by satellite peaks, due to the long-periodic magnetic structures. The profile and temperature dependence of the anomalous diffuse scattering indicate that the origin cannot be understood on the basis of magnetic short-range correlations.

Hyperfine interactions in antiferroquadrupolar ordering compound DyB2C2 studied by 161Dy Mössbauer spectroscopy on the Y-diluted system

In order to elucidate quadrupolar and magnetic interactions in the antiferroquadrupolar (AFQ) and antiferromagnetic (AFM) ordering compound DyB 2 C 2 , 161 Dy Mossbauer spectroscopy was performed on the Y-diluted system Dy 1- x Y x B 2 C 2 . The results reveal that the AFQ and AFM interactions compete with each other. The magnetic hyperfine field that is proportional to the magnetic moment strongly depends on the number and site of Y substitution in the nearest neighbors. Some kinds of Y substitution in the neighbors cause larger hyperfine fields than that in DyB 2 C 2 .