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Changes in structural modulation for the Bi2Sr2Ca1-y RE y Cu2O8+δ system (RE=Y, Nd), accompanied with the transition from the superconductor to the antiferromagnetic insulator, were examined. In the Bi2Sr2Ca1-y Y y Cu2O8+δ system, the modulation periodicity continuously decreased, from about 5.0 times to 4.0 times the length of the subcell along the b axis, with increasing Y content substituted. The modulation periodicity for Bi2Sr2NdCu2O8+δ was about 4.0 times the length of the subcell along the b axis, the same as in the Bi2Sr2YCu2O8+δ. This decrease in the modulation periodicity is attributed to the valence change of Y3+ for Ca2+.

D b r i e m e n t d'ktrophysique Relativiste et d e Cosmologie O b m t o i r e , 92190 Meudon, France AbsImacL Slatting from the equations of motion obeyed by fields, as they result from general approximations [they are m!ia to be of the following form [k2n(k)]+ = 0, for quasi bosons, and a similar equation for quasifermions] a lagmgian formalism is derived and, accordingly, consewed quantities are obtained. Next these fields are quantized and general expressions for the main observables are derived. Statistical mechanics of quasiparlicles then follow via the use of covariant Wigner functions.

We have examined electrical and magnetic properties of the Sr3V207d system. Electrical resistivity changes from metallic to semiconducting with decreasing oxygen content. Transport is governed by variable-range hopping of the electrons since the resistivity obeys the exp(AT '~) law at low temperature. Oxygen-deficient Sr3V207d exhibits different temperature-magnetic susceptibility curves for zero-field-cooled and field-cooled measurements below about 15 K. We have measured also the field dependence of the magnetic susceptibility and the long-time relaxation of thermoremanent magnetization, which obeys the relationship MTRM=At . The magnetic properties in the Sr3V207d system, therefore, are interpreted to be spin-glass-like, caused by the localized V spins introduced by the disorder-induced localization.Copper-based high-T, oxides have certain common features, such as a two-dimensional crystal structure, a -, ' spin on the Cu + ion, and the existence of the "parent" antiferromagnetic insulators, which are considered to be clues both to elucidating the mechanism for high-T, superconductivity and to searching for other high-T, super-

The inference of Ying et al. [EPL 104, 67005 (2013)] of a composition-induced change from c-axis ordered-moment alignment in a collinear A-type AFM structure (AFMI) at small x to ab-plane alignment in an unknown AFM structure (AFMII) at larger x in Ca1−xSrxCo2−yAs2 with the body-centered tetragonal ThCr2Si2 structure is confirmed. Our major finding is an anomalous magnetic behavior in the crossover region 0.2 x 0.3 between these two phases. In this region the magnetic susceptibility versus temperature χ ab (T) measured with magnetic fields H applied in the ab plane exhibit typical AFM behaviors with cusps at the Néel temperatures of ∼ 65 K, whereas χc(T) and the low-temperature isothermal magnetization Mc(H) with H aligned along the c axis exhibit extremely soft ferromagnetic-like behaviors. Much research since 2008 has focused on studies of iron-based layered pnictides and chalcogenides due to their unique lattice, electronic, magnetic and supercon-ducting properties [1-6]. An important family of these materials is comprised of doped and undoped body-centered tetragonal parent compounds AFe 2 As 2 (A = Ca, Sr, Ba, Eu) with the ThCr 2 Si 2-type structure (122-type compounds). The undoped and underdoped AFe 2 As 2 compounds exhibit a tetragonal to orthorhombic distortion of the crystal structure at T S 200 K. They also exhibit itinerant collinear antiferromagnetic (AFM) spin-density-wave ordering at a temperature T N the same or slightly lower than T S. The ordered moments in the stripe AFM structure of the orthorhombic phase are oriented in the ab plane. In 2014 a temperature T-induced AFM spin-reorientation transition to a new AFM C 4 phase was discovered in the hole-underdoped Ba 1−x Na x Fe 2 As 2 system upon cooling below T N that can coexist with superconductivity [7]. A subsequent investigation by polarized and unpolarized neutron diffraction determined that the ordered moments in the new phase are aligned along the c axis instead of along the ab plane as in the stripe AFM structure [8]. The work on the Ba 1−x Na x Fe 2 As 2 system was followed by the observation of the same AFM C 4 phase in the Ba 1−x K x Fe 2 As 2 [9-11], Sr 1−x Na x Fe 2 As 2 [12, 13], and Ca 1−x Na x Fe 2 As 2 [14] systems. These results are important to understanding the mechanism of superconductivity and other aspects of the hole-doped iron arsenides [15-21]. A similar but composition-induced moment realignment was suggested to occur in the isostructural CoAs-based system Ca 1−x Sr x Co 2−y As 2 [22]. CaCo 2−y As 2 has a so-called collapsed-tetragonal (cT) structure with As-As bonding along the c axis between adjacent CoAs layers [23] and has ≈ 7% vacancies on the Co sites [24, 25]. It exhibits itinerant A-type AFM ordering below T N = 52-77 K, depending on the sample, with the ordered moments of ≈ 0.3-0.4 µ B /Co (µ B is the Bohr magneton) within an ab-plane Co layer aligned ferromagnetically (FM) along the c axis and with AFM alignments between moments in adjacent Co planes [24-28]. The dominant interactions are found to be FM from...