High-density bulk materials of a newly discovered 40K intermetallic MgB2 superconductor were prepared by high pressure sintering. Superconducting transition with the onset temperature of 39K was confirmed by both magnetic and resistive measurements. Magnetization versus field (M-H) curve shows the behavior of a typical Type II superconductor and the lower critical field Hc1(0) estimated from M-H curve is 0.032T. The bulk sample shows good connection between grains and critical current density Jc estimated from the magnetization hysteresis using sample size was 2x10 4 A/cm 2 at 20K and 1T. Upper critical field Hc2(0) determined by extrapolating the onset of resistive transition and assuming a dirty limit is 18T

We report a coexistence of superconductivity and antiferromagnetism in five-layered compound HgBa2Ca4Cu5Oy (Hg-1245) with Tc = 108 K, which is composed of two types of CuO2 planes in a unit cell; three inner planes (IP's) and two outer planes (OP's). The Cu-NMR study has revealed that the optimallydoped OP undergoes a superconducting (SC) transition at Tc = 108 K, whereas the three underdoped IP's do an antiferromagnetic (AF) transition below TN ∼ 60 K with the Cu moments of ∼ (0.3 − 0.4)µB . Thus bulk superconductivity with a high value of Tc = 108 K and a static AF ordering at TN = 60 K are realized in the alternating AF and SC layers. The AF-spin polarization at the IP is found to induce the Cu moments of ∼ 0.02µB at the SC OP, which is the AF proximity effect into the SC OP.

We report unusual magnetic and superconducting ͑SC͒ characteristics in multilayered CuO 2 planes in Hgand Cu-based high-T c cuprates through the 63 Cu-NMR measurements. These compounds, in which the number of CuO 2 planes ͑n͒ ranges from 3 to 5 in a unit cell, include crystallographically inequivalent outer ͑OP͒ and inner ͑IP͒ CuO 2 plane that are surrounded by pyramidal and square oxygen, respectively. The Knight shift ( 63 K) at the OP and IP exhibits respective characteristic temperature dependence, consistent with its own doping level. Using an experimental relation between the spin part in 63 K at room temperature and the doping level in a CuO 2 layer N h , we show that N h (OP) at the OP is larger than N h (IP) at the IP for all the systems and its difference ⌬N h ϭN h (OP)ϪN h (IP) increases as either a total carrier content ␦ or n increases. At ⌬N h 's exceeding a critical value, the pseudogap behavior in the normal state is seen alone at the IP, and a bulk SC transition does not set in simultaneously at the IP and OP. A SC nature at the OP becomes consistent with a mean-field behavior only below T c2 that is significantly lower than T c . Reduction in T c with increasing n is associated with an increase in ⌬N h . It is a rather remarkable aspect that a T c is not always reduced even though these multilayered high-T c compounds are heavily overdoped. This arises, we show, because the IP remains underdoped and keeps a high value of T c , while the OP is predominantly overdoped. This may be a microscopic origin for the lowest anisotropic SC characteristics reported to date in Cu-based multilayered high-T c compounds.