Drastic change of the electrical resistivity related to the novel magnetic phase transition in α-Sm2S3

Magnetization and electrical resistivity of α-Sm2S3 have been investigated by using single crystals. The temperature dependence of the magnetization; M(T), demonstrates a magnetic transition at around T = 4.5 K. The M(T) shows abrupt rise below 5K with decreasing temperature in the low magnetic filed of H = 100 Oe. Zero-field-cooled M(T) shows a sudden decrease with marking a maximum at 4.5 K, while field-cooled M(T) keeps steady rising around this temperature. The magnetization M(H) in the magnetic field along the c-axis shows a ferromagnetic hysteresis at the lower temperature than TC = 4.5 K, although its magnitude is much smaller than the value for the full Sm3+ moment. The resistivity ρ(T) indicates a double peak having the maxima at T = 4.65 and 3.3 K in no magnetic field. The ratio of ρ(4.65 K) to ρ(6.0 K) is extremely large as it exceeds 100. The double peak diminishes rapidly with increasing magnetic field. The negative giant magneto-resistance effect having the magneto-resistance ratio of −99 % at H = 10 kOe has been observed at T = 4.5 K

Extremely broad hysteresis in the magnetization process of α-Dy2S3 single crystal induced by high field cooling

α-Dy2S3 possesses orthorhombic crystal structure having two crystallograpically inequivalent Dy sites. Magnetization process of α-Dy2S3 single crystal after cooling in the high magnetic field of 18 T has been investigated. The magnetization under the field of 18 T along the α-axis on the cooling process from 150 K shows step-like rises at 70 and 40 K and reaches about 9 μB per one Dy3+ at 1.5 K. This value, which corresponds to 90 % of full saturation moment of Dy3+, is much larger than 6 μB obtained at the same conditions after cooling in no magnetic field (zero-field cooling; ZFC). After cooling to 1.5 K, the magnetization while decreasing field shows abrupt drops at 3.0 and 1.7 T, and then comes to 0 μB at 0 T. Subsequently, while increasing field, the magnetization demonstrates a similar curve to that obtained after ZFC without step-like rise below 13.1 T. At μ0H = 13.1 T, the magnetization rises suddenly and agrees with the curve for the decreasing process. This irreversible magnetization process yields extremely broad hysteresis having width of μ0ΔH = 11.4 T. Broader hysteresis and narrower one are also observed at 4.2 and 10 K, respectively

Mapping dust column density in dark clouds by using NIR scattered light : Case of the Lupus 3 dark cloud

We present a method of mapping dust column density in dark clouds by using near-infrared scattered light. Our observations of the Lupus 3 dark cloud indicate that there is a well defined relation between (1) the H-Ks color of an individual star behind the cloud, i.e., dust column density, and (2) the surface brightness of scattered light toward the star in each of the J, H, and Ks bands. In the relation, the surface brightnesses increase at low H-Ks colors, then saturate and decrease with increasing H-Ks. Using a simple one-dimensional radiation transfer model, we derive empirical equations which plausibly represent the observed relationship between the surface brightness and the dust column density. By using the empirical equations, we estimate dust column density of the cloud for any directions toward which even no background stars are seen. We obtain a dust column density map with a pixel scale of 2.3 x 2.3 arcsec^2 and a large dynamic range up to Av = 50 mag. Compared to the previous studies by Juvela et al., this study is the first to use color excess of the background stars for calibration of the empirical relationship and to apply the empirical relationship beyond the point where surface brightness starts to decrease with increasing column density

Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands

We have determined the ratios of total to selective extinction directly from observations in the optical V band and near-infrared J band toward the Galactic center. The OGLE (Optical Gravitational Lensing Experiment) Galactic bulge fields have been observed with the SIRIUS camera on the IRSF telescope, and we obtain A(V)/E(V-J)=1.251+-0.014 and A(J)/E(V-J)=0.225+-0.007. From these ratios, we have derived A(J)/A(V) = 0.188+-0.005; if we combine A(J)/A(V) with the near-infrared extinction ratios obtained by Nishiyama et al. for more reddened fields near the Galactic center, we get A(V) : A(J) : A(H) : A(Ks) = 1 : 0.188 : 0.108 : 0.062, which implies steeply declining extinction toward the longer wavelengths. In particular, it is striking that the Ks band extinction is \approx 1/16 of the visual extinction A(V) much smaller than one tenth of A(V) so far employed.Comment: 8 pages, 7 figures, Accepted for publication in Ap

Van Vleck paramagnetism of the trivalent Eu ions

Magnetic susceptibilities of Eu2O3, EuF3 and EuBO3 have been measured over the wide temperature range 5 to 650 K. The Van Vleck paramagnetism, with the ground state of 7F0 (S = 3, L = 3), has been investigated comprehensively. The temperature independent paramagnetism emerges manifestly below approximately 100 K. The variation of the susceptibility with temperature for EuBO3 is in satisfactory agreement with the coupling constant λ = 471 K, where the spin-orbit interaction is λL・S for the Russell-Saunders coupling on the basis of Van Vleck theory with one parameter λ. The value of λ = 490 K can fit the susceptibility data of EuF3. The deviation from the theory arises in Eu2O3 . This discrepancy originates mainly from the influence of the crystalline field. Susceptibility of Gd2O3, having the ground state of 8S7/2 (S = 7/2, L = 0), is also presented as a magnetic standard compound in comparison with these results

Evolution from a ferromagnetic to a spin-glass regime in the spinel-type Cu(Cr1-xTix)2S4

Successive changes from ferromagnetic, re-entrant mixed, to spin-glass regime have been manifestly found with increasing Ti-composition x in the quaternary spinel-type Cu(Cr1-xTix)2S4 system. The Curie temperature Tc　decreases steeply with increasing x and this transition becomes ill-defined around x = 0.47. Two distinct transitions appear below Tc over the range x = 0.40 - 0.47. Coexistence of the ferromagnetism and spin-glass order would be observed below the Gabay and Toulouse transition TGT, owing to freezing of the transverse-spin components without changing of the ferromagnetic order parameter. Finally, at a yet lower temperature de Almeida-Thouless transition TAT, the longitudinal-spin component freezes randomly at which an irreversibility arises between zero-field-cooled (ZFC) and field-cooled (FC) magnetizations. Over the range of 0.47 ≤ x ≤ 0.85, a cusp of the ZFC magnetization is seen at Tg like conventional spin-glass. Specimens with x ≥ 0.90 remain paramagnetic down to 2.0 K. A magnetic phase diagram between T versus x has been obtained experimentally. The values of the multi critical point in 100 Oe is detected to be x = 0.47 and T = 7.40 K. The low field magnetization and the phase diagram are satisfactorily explained by the theory of Gabay and Toulouse on the basis of Heisenberg isotropic vector spin model rather than the Ising spin model

Spin-glass and novel magnetic behavior in the spinel-type Cu1-xAgxCrSnS4

A dual non-magnetic substitution system on A- and B-sites in the spinel structure has been studied. The mother compound is a ferromagnet CuCr2S4 with the Curie temperature Tc ≅ 380 K. A system of Cu1-xAgxCrSnS4, which is the same notation as (Cu1-xAgx)(Cr0:50Sn0:50)2S4, has been prepared over the entire range of 0.00≦x≦1.00 although the Cr-Sn sublattice is unchanged in the fixed composition of 0.50 on B-sites. All these compounds exhibit the spin-glass phase with the freezing temperature Tg approximately at 16 K in 100 Oe. Since only Cr ions have the magnetic moment on the B-sites, the substitution of Ag for Cu on the A-sites does not influence strongly the spin-glass freezing behavior over the whole composition range. Nevertheless, the magnetization of Cu1-xAgxCrSnS4 with x = 0.50 and 0.55 causes a broad upturn hump over 30–130 K where the spin-glass phase is broken. Strong magnetic field dependence of this hump anomaly has been observed with an irreversibility between zero-field-cooled (ZFC) and field-cooled (FC) magnetizations even though above Tg. The hump is suppressed in higher fields and collapsed down at approximately 1.0 kOe with a tiny trace quantity of the anomaly where the difference between the ZFC and FC processes disappears. The specimen with x = 0.45 shows as mall hump anomaly in low field ≦20 Oe which corresponds to a precursor of the huge anomaly for x = 0.50. The hump anomaly could be attributed to a formation of the cluster-glass. The spin-clusters are embedded in the matrix of spin-glass elements in high degree of disorder without long-range order. All the spins eventually are frozen below Tg. The strange magnetic freezing originates from the delicate dual substitutions. The mechanism of the anomaly is far from a complete picture and remains enigmatic

CHARACTERISTICS IN AN RF SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE AS A FUNCTION OF APPLIED MAGNETIC FLUX : SYSTEMATIC CALCULATIONS Ⅰ

There has been a lot of discussion of characteristics in superconducting quantum interference device (SQUID).However, much less information is available on systematic calculations of these behavior. In this report, we describe various features in a superconducting ring having one Josephson junction. Systematic computer calculations of static behavior of the rf-SQUID have been carried out. The characteristic features depend strongly on a parameter β=(2πLI₀)/Ф₀. where I₀ is a critical current of the junction. L is a self -inductance of the ring and Ф₀ is the flux quantum. In the regime β>1, the quantum states are discrete and the transitions between the quantum states are irreversible. The present work is focused on the correspondence between energy of the system and the characteristics in the rf-SQUID over the range of β= 0.20 to 2π. The results of the calculations are shown in the following No. 2 paper

A Chain of Dark Clouds in Projection Against the Galactic Center

In the J, H, and Ks bands survey of the the Galactic Center region over an area of 2deg x 5deg, we have found many dark clouds, among which a distinguished chain of dark clouds can be identified with a quiescent CO cloud. The distances of the clouds is estimated to be 3.2-4.2 kpc, corresponding to the Norma arm by our new method to determine distance to dark clouds using the cumulative number of stars against J-Ks colors. Adopting these estimated distances, the size is about 70 pc in length and the total mass of the cloud is 6x10^4 M_solar. Three compact HII regions harbor in the cloud, indicating that star forming activities are going on at the cores of the quiescent CO cloud on the spiral arm.Comment: 13 pages, 7 figures, accepted for publication in PAS