Hideaki Miyatake

First observation of an antiferromagnetic phase in the Y1Ba2Cu3Ox system

The magnetic properties of four different phases of the YBa2Cu3Ox system, including the famous 90 K superconductor, have been probed by the positive muon spin relaxation method (µ+SR). The oxygen-deficient tetragonal insulating phase (x~6.2) was found to be magnetically ordered, thus most likely antiferromagnetic, near room temperature.

μ+SR Studies of Magnetic Properties of the YBa2Cu3Ox System

Samples of YBa 2 Cu 3 O x in four different phases have been probed by positive muon spin relaxation (µ + SR) method. Each phase was found to show different magnetic behavior. In the famous orthorhombic 90K superconductor ( x ∼6.9), neither magnetic ordering nor magnetic fluctuations were observed. However, in another orthorhombic superconducting phase ( x ∼6.4, T c ≈60 K) a magnetic fluctuation was observed below 7 K via muon spin-nuclear spin double relaxation. Its magnetic ordering temperature was expected to be below 2.4 K. Similar behavior was observed in an oxygen-rich ( x ∼6.5) tetragonal insulating phase, whereas the oxygen-deficient ( x ∼6.2) tetragonal insulating phase was found to be magnetically ordered, most likely antiferromagnetic, near room temperature. This is the first observation of a magnetically ordered state in the YBa 2 Cu 3 O x system.

Observation of antiferromagnetic ordering in Bi2Sr2YCu2Oy above room temperature by the μSR method

Abstract We have observed a long-range magnetic ordering (probably an antiferromagnetic one) with a transition temperature above 300 K in Bi 2 Sr 2 YCu 2 O y by the μ + SR method. This is the first observation of the antiferromagnetic ordering with a high Neel temperature in the Bi-Sr-Ca-Cu-O system. The Bi 2 Sr 2 YCu 2 O y may be treated as an analogue of the high- T c superconductor-rela ted antiferromagnets such as YBa 2 Cu 3 O 6 or La 2 CuO 4−δ .

Positive muon sites and possibility of anyons in the YBa2Cu3O x system

Possible positive muon sites in YBa2Cu3Ox were determined from the observedμ+ hyperfine fields in antiferromagnetically ordered YBa2Cu3Ox and GdBa2Cu3O7. After determining theμ+ sites, the possibility of anyons or chiral spin ordering in the superconducting YBa2Cu3O7 is discussed. Positive muon implanted in YBa2Cu3O7 feel static magnetic fields of average 1.4G, which are explicable in terms of nuclear magnetic dipolar fields. Non observation of static local magnetic fields of electronic origin (the upper limit is the order of 0.1 G) means that anyons or chiral spin ordering might not exist in superconducting YBa2Cu3O7.

Internal magnetic fields at μ+ sites and the magnetic phase diagram of Bi2Sr2Y1−xCaxCu2Oy system studied by the μSR method

Abstract The magnetic properties of the Bi 2 Sr 2 Y 1− x Ca x Cu 2 O y system have been studied by positive muon spin rotation or relaxation methods. The magnetic phase diagram has been obtained as a function of Ca content x and temperature T . A long-range magnetic ordering (probably antiferromagnetic) has been observed in Bi 2 Sr 2 Y 1− x Ca x Cu 2 O y with Ca content x ranging from 0.0 to about 0.3. The Neel temperature T N decreases with increasing Ca content; T N is above 300 K for x =0.0, 200–250 K for x =0.2 and drops abruptly to 10–20 K for x =0.3. Superconductivity sets in around the same Ca content ( x ≈0.5) where the magnetic ordering disappears completely. The magnetic phase diagram of the Bi 2 Sr 2 Y 1− x Ca x Cu 2 O y system is thus similar to that of YBa 2 Cu 3 O x or La 2− x A x CuO 4−δ (A=Sr or Ba) and suggests a common origin of the superconductivity in all these oxide superconductors. The temperature dependence of the internal magnetic field at μ + in Bi 2 Sr 2 YCu 2 O y is also discussed.

Magnetic Phase Transitions in 90 K Superconductors HoBa2Cu3O7-δ and GdBa2Cu3O7-δ Observed by ZF- µ+SR

Freezing of holmium magnetic moments was observed below 3 K in a 90 K superconductor HoBa2Cu3O7-δ by zero-field positive muon spin relaxation (ZF-µ+SR) measurements. The ZF-µ+SR function revealed a marked change of µ+ local field from a critically fluctuating regime (4–7 K) to a quasi-static regime below 3 K (of nearly Gaussian distribution). The observation indicates that holmium magnetic moments are short-range ordered around 2 K. In contrast, a 90 K superconductor GdBa2Cu3O7-δ showed a zero-field spin precession at 2 K, indicating long-range ordering of gadolinium magnetic moments.

Observation of an Antiferromagnetic Phase in the Bi 2 Sr 2 CuO 6+ y System by the μ + SR Technique

We have observed antiferromagnetic ordering in the insulating phase ( x ≥0.50) of the single-CuO 2 -layer (per unit cell) Bi 2 (Sr 1- x La x ) 2 CuO 6+ y system. The Neel temperature increases from 10 K to 140 K with increasing La concentration. In this respect the system behaves like other high- T c copper oxide superconductors. In both x =0.55 and x =0.60 specimens, two hyperfine magnetic fields (45 G and 300 G) were observed at different µ + sites in the crystal.

Magnetic properties and magnetic phase diagram of (RE) Ba2Cu3Ox system studied by positive muon spin relaxation

Magnetic phase diagram of the (RE)Ba 2 Cu 3 O x (RE=Y, Ho) system against the oxygen content was obtained by μ + SR. Antiferromagnetic ordering of YBa 2 Cu 3 O x was found not to be influenced by the replacement of Y by Ho. The interaction between rare-earth atoms and electrons in 2-dimensional Cu-O planes was shown to be very weak.

Probing magnetism of high-Tc superconductor Y−Ba−Cu oxide by positive muons

Magnetic properties of a newly discovered high-Tc superconductor, Y-Ba-Cu oxide, were studied by zero-field positive muon spin relaxation method in a zero external magnetic field. Some kind of a magnetic phase transition was found at a temperature between 10 K and 27 K. It is discussed how this magnetism relates to the superconductivity.