Hiroki Morodomi

Spin-Liquid Ground State in the Spin 1=2 Distorted Diamond Chain Compound K3Cu3AlO2(SO4)4

The new compound K3Cu3AlO2(SO4)4, representing a spin 1/2 distorted diamond chain system, was synthesized and its magnetic properties were studied by magnetic susceptibility, specific heat, and high-field magnetization measurements. Magnetic Cu2+ ions were found to form a highly one-dimensional distorted diamond chain with strong intrachain interactions. Short-range magnetic correlations were observed to develop in a two-stage process without magnetic long-range ordering by magnetic susceptibility and specific heat measurements. The exchange constant ratio J2/J1, where J2 is the magnetic interaction of the diamond backbone and J1 is the magnetic interaction of the monomers along the chain, was estimated to be 2.5, demonstrating that the magnetic ground state is composed of an alternating dimer–monomer spin-liquid phase. The absence of an M = 0 plateau in the high-field magnetization curve is also consistent with an alternating dimer–monomer model. These results strongly suggest that K3Cu3AlO2(SO4)4 is the...

New phase diagram of PrPb3 in [100] magnetic filed direction

We measured the magnetic field dependence of the specific heat in PrPb 3 in the field direction H ∥[100] up to H =8 T. At H =0 T, an antiferro-quadrupole ordering occurs at T Q =0.43 K, which is higher than T Q =0.4 K in previous measurements, and is evidence of the high quality of the sample. We describe a new T – H phase diagram in H ∥[100]. Note that a high-field phase appears above the low-field phase with the O 2 0 order parameter, which is likely the O 2 2 phase assisted by the octupole moment.

Magnetic phase diagram of DMACuCl3

Result of specific heat measurements on the single crystal of DMACuCl3 is presented and compared with previous one obtained for the powder crystal. Possible reason for the marked difference between them is discussed on the basis of competition between critical fluctuation in the magnon BEC process and short correlation length in the powder crystal.

Anomaly of Specific Heat in High Quality Single Crystal of PrAg2In

PrAg2In has a non-Kramers doublet Λ3 ground state, which is expected to show a quadrupolar phenomena. Although many studies have been devoted to investigate the novel features of PrAg2In, there is no clear result how to remove the degeneracy of quadrupolar moment because this compound has a Heusler structure, in which the substitution between Pr and In ions is inevitable. We therefore prepare a high quality single crystal of PrAg2In with the residual resistivity ratio of 14, which is much larger than that of the previous samples. We measure the magnetic susceptibility with the SQUID magnetometer down to T = 0.4 K and the specific heat in the magnetic fields up to H = 8T along [100] crystal direction down to T =0.1 K. The susceptibility is consistent with the CEF calculation. The specific heat shows a sharp peak at around Tp = 0.33 K. When the magnetic field is applied, the peak at TP does not move up to H = 2.5 T. In contrast, it shifts to higher temperatures with broadening above H = 2.5 T. The broad peak above H = 2.5 T is well reproduced by the Schottky specific heat due to the splitting of the Λ3 doublet in the magnetic fields. From these results, we conclude that a phase transition related to the r3 doublet occurs at around TP.

Low-temperature magnetization study of spin gap system (CH 3)2NH2CuCl3 with nanometer particle size

So far specific heat measurements for the title compound have revealed that the magnetic field vs. temperature phase diagram depended significantly on the system size. For instance, the single crystal showed the spontaneous magnetic ordered phase in low fields and the field induced one in high fields separated by the magnetization plateau range at around 3 T, while the powder sample with typically nanometer particle size showed a quite different trend that field induced magnetic ordered phase extended to zero field. In this study, we measures dc magnetization of powder sample and nano-sized powder sample. Measurements were performed down to the lowest temperature of 0.5 K using commercial Quantum Design MPMS equipped with homemade 3He refrigerator insert. Most remarkable feature is that 1/2 plateau was not observed clearly in the magnetization process for the nano-sized powder sample indicating the disappearance of the spin gap.

Magnetic Ordering of Antiferromagnetic Trimer System 2b·3CuCl2·2H2O

In this paper, we present the magnetic properties of 2b3CuCl22H2O (b = betaine, C5H11NO2). 2b3CuCl22H2O is the first model substance for a two-dimensional S = 1/2 orthogonal antiferromagnetic trimer system. We have performed magnetic susceptibility, magnetization curve, and specific heat under extreme conditions: low temperatures and high magnetic fields in this system. The experimental results indicate that this substance is a magnetically S = 1/2 antiferromagnetic trimer system. The magnetization also shows one-third of the saturation value (MS ~ 3.2μB/f.u.) between 5 and 14T The specific heat in a zero field shows a sharp peak at 1.38K corresponding to a long-range magnetic ordering, TN. As the magnetic field increases, the TN shifts remarkably to a lower temperature and is suppressed. Above 5T, the specific heat has no anomaly down to 150mK In the plateau region with an energy gap, the magnetic ordering seems to be disappeared.

Specific heat study of geometrically frustrated magnet clinoatacamite Cu2Cl(OH)3

We have performed the specific heat study in a new geometrically frustrated system, clinoatacamite Cu2Cl(OH)3 with the corner-sharing tetrahedron structure of the Cu2+ ions with 5=1/2 Heisenberg spin. At H=0 T, two anomalies are observed at T2=18.1 K and at T2=6.2 K. The specific heat decreases rapidly below T2 and shows no anomaly down to T=150 mK despite the existence of the spin fluctuation shown in the μSR experiments. As the magnetic field is increased, the sharp peak at T2 is broadened and shows a small reentrant behavior in the T – H phase diagram. On the other hand, the peak at T1 shows no obvious change up to H=5 T. The entropy at T1 is estimated as ~0.35Rln2 at H=0 T. These features may be caused by the two dimensional nature of the kagome antiferromagnets which are weakly coupled via Cu2+ ions at the triangular sites located in between the kagome layers.

Cluster-Based Haldane State in an Edge-Shared Tetrahedral Spin-Cluster Chain: Fedotovite K2Cu3 O (SO4)3

Fedotovite K_{2}Cu_{3}O(SO_{4})_{3} is a candidate of new quantum spin systems, in which the edge-shared tetrahedral (EST) spin clusters consisting of Cu^{2+} are connected by weak intercluster couplings forming a one-dimensional array. Comprehensive experimental studies by magnetic susceptibility, magnetization, heat capacity, and inelastic neutron scattering measurements reveal the presence of an effective S=1 Haldane state below T≅4  K. Rigorous theoretical studies provide an insight into the magnetic state of K_{2}Cu_{3}O(SO_{4})_{3}: an EST cluster makes a triplet in the ground state and a one-dimensional chain of the EST induces a cluster-based Haldane state. We predict that the cluster-based Haldane state emerges whenever the number of tetrahedra in the EST is even.

Unusual magnetic ordering observed in nanosized S = 1/2 quantum spin system (CH3)2NH2CuCl3

Specific heat measurements were performed on nanometer-sized particles of an S = 1/2 quantum spin system, DMACuCl3 [DMA = (CH3)2NH2]. A tiny peak was observed at a low temperature of approximately 1.5 K at zero magnetic field, in addition to a well-defined and commonly observed peak with the bulk system at approximately 0.8 K. Under magnetic fields, it increased in intensity and coincided with the phase boundary responsible for the field-induced magnetic ordering phase above about 6 T. 1H-NMR studies confirmed that such extra peaks also indicated magnetic ordering. The resultant phase diagram is considerably different from that observed previously in the bulk system. Such a difference may be caused by the presence of extra spins found in a nanosized system by ESR measurements.

Susceptibility measurements in PrxLa1-xInAg 2 with Γ3 doublet ground state

We have measured the susceptibility and magnetization of PrxLa1-xInAg2 at Pr concentrations x=1 and 0.1 down to T ~ 0.5 K by SQUID magnetometer with a home-made 3He insert. The susceptibility above T = 15 K is well reproduced by the crystal-electric-field level scheme with a non-Kramers Γ3 doublet in the ground state for each concentration, while that below T = 15 K shows a non-Fermi-liquid (NFL) behavior with — ln T-dependence at low magnetic field. With increasing magnetic field, — ln T-dependence is suppressed and —T1−2-dependence appears at H = 7 T The magnetization at T = 0.5 K increases with increasing magnetic fields up to H = 7 T, indicating that the increase of the susceptibility does not come from impurity ions. These results suggest that the quadrupolar Kondo effect is responsible for NFL behavior of the susceptibility.