Frustrated magnetism and the effects of titanium substitution in the mixed-valence oxide BaV{sub 10-x}Ti{sub x}O{sub 15}

Journal Article · Sat Jul 01 00:00:00 EDT 2006 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.74.024426· OSTI ID:20853331

Bridges, Craig A ^[1]; Hansen, T ^[2]; Wills, A S ^[3]; Luke, G M ^[4]; Greedan, J E ^[5]

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1. Department of Chemistry, University of Liverpool, Liverpool L697ZD (United Kingdom)
2. Institute Laue Langevin, 6 Rue Jules Horowitz, 32042 Grenoble (France)
3. Department of Chemistry, University College London, 20 Gordon Street, London WC1H OAJ (United Kingdom)
4. Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, L8S 4M1 (Canada)
5. Brockhouse Institute for Materials Research and Department of Chemistry, McMaster University, Hamilton, Ontario, L8S 4M1 (Canada)

The low temperature magnetic phase transitions in BaV{sub 10}O{sub 15} at {approx}40 K and {approx}25 K are investigated in detail. The topology of the V sublattice, which consists of linked V{sub 10} clusters formed by four tetrahedra sharing edges and corners, leads to geometric magnetic frustration and a depression of the ordering temperature characterized by the frustration index, f=vertical bar {theta} vertical bar/T{sub c}{approx}30. Specific heat data show the coexistence of both long range and short range magnetic order at low temperature. The position of a {lambda} peak, identified with T{sub c} for long range antiferromagnetic order, depends on the V{sup 2+}/V{sup 3+} ratio and varies from 43.0 K to 41.6 K for samples with the highest V{sup 2+} content but is suppressed to zero for highly oxidized samples. A broad maximum in the specific heat occurs at {approx}25 K and is present in all samples regardless of the level of oxidation. For samples with a well defined T{sub c}, estimates of the entropy removal over the range 5 K to 55 K are only 11% of that expected for 8 V{sup 3+}(S=1) and 2 V{sup 2+}(S=3/2) ions per formula unit, suggesting the presence of considerable short-range order. Neutron diffraction data support the presence of long range antiferromagnetic (AF) order with T{sub c}{approx}40 K. The magnetic structure below T{sub c} is complex: there are five crystallographically independent vanadium ions in the unit cell, leading to 40 magnetic ions in the crystal unit cell and 80 spins per magnetic cell. Furthermore, the magnetic structure is of the multi-k type involving the two unrelated wave vectors k=(0 0 0) and k=(1/2 0 0). Zero field muon spin relaxation data show spin freezing below 30 K. ac susceptibility results are anomalous. Two peaks, at {approx}0 K and {approx}25 K are seen in {chi}{sup '} but the maxima are frequency independent as is the prominent maximum in {chi}{sup ''} near 25 K, behavior atypical of spin glasses. Ti-doped samples, BaV{sub 10-x}Ti{sub x}O{sub 15}, show remarkable results as only 5% Ti doping is sufficient to destroy the AF long range order and induce conventional spin glass behavior in the dc and ac susceptibility, with freezing temperatures ranging from 15 K-5 K for doping levels from 5% to 50%. The frustration indices reach enormous values to f=130 for x=3. The spin glass state is quenched for 70% Ti doping and only paramagnetic behavior is seen.

• OSTI ID: 20853331
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 74, Issue 2; Other Information: DOI: 10.1103/PhysRevB.74.024426; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ANTIFERROMAGNETIC MATERIALS
ANTIFERROMAGNETISM
BARIUM COMPOUNDS
CRYSTALS
CURIE POINT
DOPED MATERIALS
ENTROPY
FREEZING
MAGNETIC SUSCEPTIBILITY
MUON PROBES
MUON SPIN RELAXATION
NEUTRON DIFFRACTION
OXIDATION
PARAMAGNETISM
SPECIFIC HEAT
SPIN
SPIN GLASS STATE
TITANATES
TITANIUM
VALENCE
VANADIUM COMPOUNDS
VANADIUM IONS