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

Specific-heat study on successive magnetic transitions in α-Dy2S3 single crystals under magnetic fields

Specific heat measurements in magnetic fields have been performed on !-Dy2S3 single crystal that shows successive magnetic transitions at TN1 = 11.4 K and TN2 = 6.4 K. The specific heat in no magnetic field exhibits sharp peaks at both temperatures of TN1 and TN2.The change of magnetic entropy across each transition is estimated as Rln2/2 per mol-Dy,which suggests magnetic moments on only one Dy site between two crystallographically inequivalent Dy sites order at each transition temperature. When the magnetic field is applied along the b-axis of the orthorhombic system, two peaks of the specific heat shift toward lower temperatures. On the other hand, the magnetic field perpendicular to the b-axis shifts the peaks toward higher temperatures. The TN1 shifts to 9.6 K (H// b) and 12.5 K (H⊥b) under the magnetic field of 2 T. The peak of TN2 broadens gradually with increasing magnetic field for each direction, and the peak is consequently obscure under the field of 2 T

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

Extremely anisotropic suppression of huge enhancement of electrical resistivity by magnetic field in α-R2S3 (R = Sm, Dy).

The electrical resistivity ρ and magnetization M of α-R 2S3 (R = Sm, Dy) single crystals have been measured in various magnetic fields lying in the ac-plane of an orthorhombic crystal structure. The measurements have been carried out by rotating the single crystals around the b-axis (being set parallel to a horizontal direction), corresponding to the longitudinal direction of needle-shaped single crystals, in vertical magnetic fields. The electrical resistivity under no magnetic field shows huge enhancement in a narrow temperature range around the successive magnetic transition temperatures, as reported previously. Such enhancement is suppressed rapidly by applying a magnetic field, which has been clearly seen as diminishing of the ρ(T) peak. The magnetic field along the easy magnetization axis; H easy, moves the ρ(T) peak toward higher temperature with diminishing it, while the magnetic field along the hard magnetization axis; H hard, moves it to lower temperature. The suppression effect is extremely anisotropic for the orientation of the magnetic field lying in the ac-plane. It has been concluded that H easy suppresses the ρ enhancement most strongly. The suppression effect under H easy is more than 200 times larger at least in some cases than that under H hard

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

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

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

Specific heat in magnetic field and magnetocaloric effects of α-R2S3 (R = Tb, Dy) single crystals

The magnetocaloric effects (MCE) of α-Tb2S3 and α-Dy2S3 single crystals exhibiting successive antiferromagnetic (AFM) transitions have been investigated by analyzing specific heat measured in magnetic field. The temperature dependence of specific heat in the vicinity of the successive transitions shows obvious distinction depending on the orientations of the applied magnetic field for both α-Tb2S3 and α-Dy2S3 that having orthorhombic crystal structures. When the magnetic field is increased, the specific heat is as follows: For α-Tb2S3 in H‖b, the peak around TN2 shifts to lower temperature but the other one peak around TN1 barely moves; In H⊥b, the peak around TN2 has no shift almost within 3 T but suddenly moves to lower temperature in 4 T and the other one peak around TN1 shifts to lower temperature in specific heat versus temperature. In the case of α-Dy2S3, the two peaks around TN2 and TN1 shift to lower temperatures in H‖b but move to higher temperatures when the magnetic field is increased up to 5 T by H⊥b in spite of antiferromagnetic transitions. Therefore, the maximum value and corresponding temperature of both isothermal magnetic entropy change (ΔSm) and adiabatic temperature change (ΔTad) in the magnetic field H⊥b are extremely different in low temperature range from that in the field of H‖b. The results propone that the MCE of α-Tb2S3 and α-Dy2S3 could be controlled at low temperature by the magnitude and orientation of magnetic field. It also indicates that the refrigerating capacity and thermal absorption capacity will be controlled by changing magnitude and orientation of magnetic field on the α-Tb2S3 and α-Dy2S3 single crystals

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