Browsing by Author "HO, JC"

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ANISOTROPIC MAGNETIC-PROPERTIES OF BI2SR2CUO6+DELTA SINGLE-CRYSTAL
(1992-07-01)
SHI, JB
;
CHIOU, BS
;
HO, JC
;
KU, HC
;
電控工程研究所
Single crystals of Bi2Sr2CuO6+delta were synthesized and characterized by X-ray diffraction. The Bi(2201) sample remains not superconducting or magnetically ordered down to 5 K. With an applied magnetic field perpendicular or parallel to the c-axis, magnetic measurements yielded anisotropic magnetic susceptibilities chi(c)(H perpendicular-to c) and chi(ab)(H parallel-to c). Both can be fitted to the sum of a temperature-independent chi(0) and a Curie-Weiss term C/(T + theta(p)) in the temperature range between 5 and 300 K, with a common Curie constant C = 1.0 x 10(-2) cm3 K/mol and Curie-Weiss paramagnetic intercept theta(p) = + 1.1 K. Since the resulting Curie-Weiss term is the same for both directions, the overall anisotropy DELTA(chi) = chi(c) - chi(ab) = DELTA(chi-0) is also temperature independent. Its magnitude, 3.3 x 10(-5) cm3/mol, however, is lower than the corresponding values for Bi(2212) (2.3 x 10(-4) cm3/mol) and Bi(2223) (5.8 x 10(-4) cm3/mol).
ANOMALOUS PR ORDERING IN THE NEW TLBA2PRCU2O7-DELTA COMPOUND
(1992-11-01)
LAI, CC
;
CHIOU, BS
;
CHEN, YY
;
HO, JC
;
KU, HC
Magnetic measurements on the new tetragonal Tl(1212) compound TlBa2PrCu2O7-delta (a = 3.910 angstrom and c = 12.53 angstrom) reveal an anomalously high antiferromagnetic Neel temperature T(N) congruent-to 8 K. This transition temperature is higher than T(N) = 2.2 K for isostructural TlBa2GdCu2O7-delta. Corroborative evidence comes from calorimetric studies, in which a magnetic entropy was obtained DELTAS congruent-to 0.5 Rln 2 between 2 and 10 K, as well as a sizeable linear term in specific heat comparable to those found in heavy-fermion systems. Through structural consideration, these observations can not only be correlated to the almost identical but still puzzling features of PrBa2Cu3O7-y, but also remove some ambiguity in the interpretation of earlier results.
COBALT ORDERING IN LAYERED BI2SR2COO6+DELTA-SINGLE CRYSTAL
(1993-01-15)
SHI, JB
;
HO, JC
;
LEE, TJ
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CHIOU, BS
;
KU, HC
Insulating Bi2Sr2CoO6+delta is nearly isomorphic with the Bi(2201)-type high-T(c) superconductors. Magnetic and calorimetric studies were carried out on single crystal samples of this layered compound. Based on magnetic measurements, the cobalt ions undergo a canted antiferromapetic ordering at T(N) = 159 K. A low-temperature neutron diffraction study of the magnetic structure is in progress. The molar magnetic susceptibility chi(ab)(H perpendicular-to c) above 200 K can be well fitted by the Curie-Weiss form chi(ab)(T) = chi0+C/(T-theta(p)), with chi0 = 0.56 cm3K/mol, Curie constant C = 3.2 x 10(-2) cm3K/mol and Curie-Weiss intercept theta(p) = 159 K. There is no magnetic specific heat peak, however, prevailing around T(N). This anomalous calorimetric behavior is attributed to the two-dimensional quantum spin fluctuation of Co spins above T(N) in the layered compound as previously observed for Cu spins in (Gd1.85Ce0.15)CuO4-delta and La2CuO4-delta.
COMPARATIVE-STUDIES OF GD-ORDERING IN VARIOUS CUPRATE SYSTEMS
(1994-02-01)
HO, JC
;
WU, CY
;
LAI, CC
;
SHIEH, JH
;
KU, HC
Gd-ordering near 2.2 K in both superconducting and nonsuperconducting GdBa2Cu3O7-y has been well documented. This report summarizes our results from comparative studies on other Gd-containing cuprates (with well-defined Neel temperatures in parentheses) including Bi2Sr2GdCu2O8 (1.6 K), TlBa2GdCu2O7 (2.2 K), TlSr2GdCu2O7 (2.4 K), (Pb.5Cu.5)Sr2GdCu2O7 (2.3 K), Pb2Sr2GdCu3O8 (2.3 K), Gd2CuO4 (6.6 K) and (Gd1.85Ce0.15)CuO4 (5.3 K). The Neel temperature values for the Bi-, Tl-, and Pb-based cuprates remain close to that for PrBa2Cu3O7-y having similar layered structures but somewhat different Gd-Gd distance along the c-axis, whereas the T'(214) compounds become ordered at higher temperatures. Also to be noted is the general occurrence of a broad shoulder below the heat capacity peak, which needs to be taken into account for obtaining the expected magnetic entropy DELTAS = Rln8 associated with the ordering.
MAGNETIC AND CALORIMETRIC STUDIES OF GD ORDERING IN TLBA2GDCU2O7-DELTA
(1993-05-01)
CHEN, YY
;
LAI, CC
;
CHIOU, BS
;
HO, JC
;
KU, HC
Antiferromagnetic ordering among Gd3+ ions in the nonsuperconducting compound TiBa2GdCu2O7-delta occurs near 2.2-2.3 K as confirmed by magnetic and calorimetric measurements. This compound is similar in structure to that of superconducting GdBa2Cu3O7-y, but with the Cu-O chains replaced by Tl-O planes, which also exhibits a similar magnetic transition at 2.2-2.3 K. This paper further compares the Neel temperatures and magnetic specific-heat anomalies of various Gd-containing compounds and related systems. Some common features between the compounds are discussed.
MAGNETIC-BEHAVIOR IN PR-CONTAINING TL-BASED AND PB-BASED CUPRATES
(1994-02-01)
KU, HC
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LAI, CC
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SHIEH, JH
;
LIOU, JW
;
WU, CY
Magnetic ordering among Pr ions occurs at a relatively high temperature of 17 K in PrBa2Cu3O7, but is absent in Pr2CuO4 and Bi2Sr2PrCu2O8 above 1.6 K. This work extends the study of magnetic properties to other Pr-containing cuprates including TlBa2PrCu2O7, (Pb.6Cu.4)Sr2PrCu2O7 and Pb2Sr2PrCu3O8. Low temperature calorimetric and SQUID measurements show broad peaks in C and dchi/dT in all cases. The onset temperatures are near 10 K, while the maxima in C as well as minima in dchi/dT prevail at about 8 to 5 K. The heat capacity data provides additional information concerning the entropy associated with the magnetic anomalies and large contributions seemingly linear with temperature.