Electrical and Magnetic Properties in Bi₂Sr₂Ca_1-xY_xCu₂O_8+δ

Abstract

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...

Stoichiometric transfer of material in the infrared pulsed laser deposition of yttrium doped Bi-2212 films

“…At higher Y doping, the carrier concentration fall as low as 1.09 Â 10 20 carriers/cm 3 . This is consistent with the previous observation in bulk Y-doped samples with x approaching 0.5 values showing non-superconducting behavior [29]. This property of the film is due to the fact that IR-PLD transfers material stoichiometrically.…”

Lattice Effect on the Superexchange Interaction in Antiferromagnetic Bi2.1Sr1.9CaCu2O8+δ

“…43 The T N value obtained for the studied antiferromagnetic Bi 2.1 Sr 1.9 CaCu 2 O 8+δ compound is 20 K higher than those in the Bi 2 Sr 2 Ca 1−x Y x Cu 2 O 8+δ system. 41 This result confirms the strong antiferromagnetic properties of our sample. The relatively high T N also correlates with minimal excess oxygen content.…”

Electronic band structure ofBi2Sr2Satō1, Horiba2, Nagasaka3 1993Phys. Rev. Lett.

“…Therefore, the carrier concentration is mainly determined by 1 -x. On the other hand, the critical value of x of the metal-nonmetal transition, which was studied by a solid reaction method, is about 0.5 [8,14], while that of ours is about 0.4. This discrepancy may arise from the fact that Y atoms are more easily substituted than Ca atoms in the case of the flux method.…”