2007/11/08 by N. Tristan, V. Zestrea, G. Behr +7
Chemistry · Materials Science · Physics and Astronomy · #Advanced Condensed Matter Physics #Antiferromagnetism #Chemistry #Condensed matter physics #Crystallography #Curie temperature #Ferromagnetism #Frustration #Heat capacity #Magnetic and transport properties of perovskites and related materials #Magnetic susceptibility #Materials science #Multiferroics and related materials #Physics #Spin glass #Spinel #Superexchange #Thermodynamics #cond-mat.mtrl-sci #cond-mat.other
paper · pdf · doi:10.1103/physrevb.77.094412
19 pages, 9 figures, 46 references
arxiv created 2007/11/08 · openalex publication_date 2008/03/17 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We report on x-ray diffraction, magnetic susceptibility, electron-spin resonance, and heat-capacity studies of Co[Al_1\ensuremath-xCox]2O4 for Co concentrations 0\ensuremath\leqslantx\ensuremath\leqslant1. In this spinel system only the A-site Co2+ cation is magnetic, while the nonmagnetic B-site Al3+ is substituted by the low-spin nonmagnetic Co3+, and it is possible to investigate the complete phase diagram from Co2+Al3+2O4 to Co2+Co3+2O4. All samples reveal large negative Curie-Weiss temperatures \ensuremathΘCW of the order of \ensuremath-110\phantom\rule0.3em0exK independent of concentration, which is attributed to a high multiplicity of the superexchange interactions between the A-site Co2+ cations. A pure antiferromagnetic state is found for x=1.0 and 0.9 with N'eel temperatures TN=29.5 and 21.2\phantom\rule0.3em0exK, respectively, as evidenced by lambdalike anomalies in the specific heat. Compositions with 0.3\ensuremath\leqslantx\ensuremath\leqslant0.75 show smeared out strongly reduced magnetic ordering temperatures. At low temperatures, a T2.5 dependence of the specific heat is indicative of a spin-liquid state. For x\ensuremath\leqslant0.2 a T2 dependence of the specific heat and a spin-glass-like behavior of the susceptibility below Tf\ensuremath∼4.7\phantom\rule0.3em0exK are observed. The high value of the frustration parameter f=\ensuremath|\ensuremathΘCW\ensuremath|∕Tf>10 indicates the presence of strong spin frustration at least for x\ensuremath\leqslant0.6. The frustration mechanism is attributed to competing nearest-neighbor and next-nearest-neighbor superexchange interactions between the A-site Co2+ ions.