Partial antiferromagnetism in spin-chainSr5Rh4O12,Ca

Abstract

We report a structural, thermodynamic, and transport study of the newly synthesized Sr 5 Rh 4 O 12 , Ca 5 Ir 3 O 12 , and Ca 4 IrO 6 single crystals. These quasi-one-dimensional insulators consist of a triangular lattice of spin chains running along the c axis, and are commonly characterized by a partial antiferromagnetic ͑AFM͒ order, a small entropy removal associated with the phase transitions, and a sizable low-temperature specific heat linearly proportional to temperature. Sr 5 Rh 4 O 12 is antiferromagnetically ordered below 23 K with strong evidence for an Ising character. Isothermal magnetization of Sr 5 Rh 4 O 12 exhibits two steplike transitions leading to a ferrimagnetic state at 2.4 T and a ferromagnetic state at 4.8 T, respectively. Ca 5 Ir 3 O 12 and Ca 4 IrO 6 are also antiferromagnetically ordered below 7.8 and 12 K, respectively, and show an unusually large ratio of the Curie-Weiss temperature to the Néel temperature. In particular, Ca 5 Ir 3 O 12 , which includes both Ir 4+ and Ir 5+ ions, reveals that only S =1/2 spins of the Ir 4+ ions are involved in the magnetic ordering, whereas S = 1 spins of the Ir 5+ ions remain disordered. All results suggest the presence of a geometrical frustration that causes incomplete long-range AFM order in these quasi-one-dimensional compounds.

Measurement of the internal magnetic field in the correlated iridates Ca4IrO6, CaFranke1, Baker2, Blundell3 et al. 2011Phys. Rev. BSelf Cite494312View full textAdd to dashboardCite

“…Ca 4 IrO 6 has a rhombohedral structure, in which 1D chains of IrO 6 octahedra alternate with CaO 6 trigonal prisms 3,12 . In contrast Ca 5 Ir 3 O 12 has a triangular lattice and a hexagonal structure 4,15 and, unusually amongst iridates, in addition to Ir 4+ it also includes Ir 5+ ions.…”

“…A wide variety of behavior can be expected since the transition metal ion can be any one of the 3d, 4d or 5d series and the possible crystal architectures that can be synthesized include chains, ladders, square layers, triangular layers, kagome layers, pyrochlore lattices and many more. The 5d series has received the least attention but the extended nature of the 5d orbitals leads to large crystal field energies 3 . The spin-orbit interaction is also strong, owing to the large atomic number, and these competing energy scales are likely to open up new possibilities for their magnetic behavior.…”

“…For example, Ca 4 IrO 6 and Ca 5 Ir 3 O 12 are antiferromagnetically ordered at low temperature but exhibit weak ferromagnetism due to spin canting 3,4 . Ca 5 Ir 3 O 12 exhibits a more complex partial spin ordering due to the presence of both Ir 4+ and Ir 5+ ions 3 .…”

Crossover of conduction mechanism in Sr2IrO4 epitaxial thin films

“…In recent years, oxides with the 5d-element Ir have been established as a fertile ground for studying new physics arising from the large relativistic spin-orbit-coupling (SOC) [1][2][3]. So far, a variety of exotic properties related to the strong SOC such as intriguing insulating behavior [3][4][5][6][7][8][9][10] In addition to the newly raised controversy on the insulating nature of SIO, the conduction mechanism of the insulating state has been a long-standing issue. In an early work, variable range hopping (VRH) conduction was reported in single crystalline SIO [3].…”

One-dimensional magnetic order in the metal-organic framework Tb(HCOO)3

“…long-wavelength incommensurate spin density modulations and field-induced magnetisation plateaux reminiscent of Hofstadter fractalisation [9,10]. In the field of low-dimensional magnetism, arguably the strongest scientific interest from both experimental and theoretical perspectives has always been in the limit of strict 1D order [11][12][13][14][15][16]. Yet even in canonical systems such as Ca 3 Co 2 O 6 the divergence of correlation lengths along 1D spin chains is always accompanied by full 3D magnetic order [8,17].…”