O17andV51NMR for the zigzag spin-1 chain compound

Xiaopeng Zong

¹

,

B. J. Suh

²

,

A. Niazi

³

et al.

Abstract

Abstract51V NMR studies on CaV 2 O 4 single crystals and 17O NMR studies on 17O-enriched powder samples are reported. The temperature dependences of the 17O NMR linewidth and nuclear spin-lattice relaxation rate give strong evidence for a long-range antiferromagnetic transition at T N =78 K in the powder. Magnetic susceptibility measurements show that T N =69 K in the crystals. A zero-field 51V NMR signal was observed at low temperatures (f≈237 MHz at 4.2 K) in the crystals. The field-swept spectra with the field in different directions suggest the presence of two antiferromagnetic substructures. Each substructure is collinear, with the easy axes of the two substructures separated by an angle of 19(1)°, and with their average direction pointing approximately along the b axis of the crystal structure. The two spin substructures contain equal numbers of spins. The temperature dependence of the ordered moment, measured up to 45 K, shows the presence of an energy gap E G in the antiferromagnetic spin wave excitation spectrum. Antiferromagnetic spin wave theory suggests that E G ∕k B lies between 64 and 98 K. 17 O NMR linewidth and nuclear spin-lattice relaxation rate give strong evidence for a long-range antiferromagnetic transition at T N = 78 K in the powder. Magnetic susceptibility measurements show that T N = 69 K in the crystals. A zero-field 51 V NMR signal was observed at low temperatures ͑f Ϸ 237 MHz at 4.2 K͒ in the crystals. The field-swept spectra with the field in different directions suggest the presence of two antiferromagnetic substructures. Each substructure is collinear, with the easy axes of the two substructures separated by an angle of 19͑1͒°, and with their average direction pointing approximately along the b axis of the crystal structure. The two spin substructures contain equal numbers of spins. The temperature dependence of the ordered moment, measured up to 45 K, shows the presence of an energy gap E G in the antiferromagnetic spin wave excitation spectrum. Antiferromagnetic spin wave theory suggests that E G / k B lies between 64 and 98 K.

Single-crystal growth, crystallography, magnetic susceptibility, heat capacity, and thermal expansion of the antiferromagneticS=1chain compoundCaV2ONiazi1, Bud’ko2, Schlagel3 et al. 2009Phys. Rev. BSelf Cite333550View full textAdd to dashboardCite

“…10,11 In single crystals, at temperatures below 45 K we do find a zero-field 51 V NMR signal where the 51 V nuclei resonate in the static component of the local magnetic field generated by the long-range AF order below T N Ϸ 70 K. 14 The ordered moment at 4.2 K in the crystals was estimated from the zero-field 51 V NMR measurements to be 1.3͑3͒ B / ͑V atom͒, somewhat larger than but still consistent with the value 1.06͑6͒ B / ͑V atom͒ from the above neutron diffraction measurements. 13 An energy gap ⌬ for antiferromagnetic spin wave excitations was found with a value ⌬ / k B =80͑20͒ K in the temperature range of 4-45 K, where k B is Boltzmann's constant.…”

“…As discussed in Sec. I, our recent NMR and magnetic neutron diffraction experiments on single crystal CaV 2 O 4 indicated that the magnetic structure at 4 K is noncollinear, 14,15 which can at least partially explain the nonzero spin susceptibility along the ͑average͒ easy b axis at low temperatures. In addition, the reduction in the local ordered moment ͑1.0-1.6͒ B / ͑V atom͒ of the ordered vanadium spins found in these studies from the expected value gS B =2 B / ͑V atom͒ suggests that quantum zero-point spin fluctuations could be strong and could contribute to the large finite b spin ͑T → 0͒.…”

Synthesis and structural, magnetic, thermal, and transport properties of several transition metal oxides and aresnides

“…The Ca atoms are located in between these chains. The system undergoes an orthorhombic to monoclinic structural distortion at a sample-dependent T S ≈ 108 − 145 K and an antiferromagnetic transition with noncollinear spin structure at a sample-dependent T N ≈ 50 − 70 K. [40][41][42] A peak in the heat capacity versus temperature at T ∼ 200 K has been observed which might be the long-sought chiral phase transition. A detailed study involving synthesis of polycrystalline and single crystal samples of CaV 2 O 4 , and investigation of magnetic, structural, and thermal properties of the samples, is given in Appendix A of this thesis.…”

“…[40,41] This unusual magnetic susceptibility provided us with a strong motivation to further study this class of materials and the results are described in Ch. 7 of this thesis.…”

“…This result is consistent with our observed noncollinear magnetic structure below T N . [150,151] In view of the fact that CaV 2 O 4 is a low-dimensional spin system, quantum fluctuations could also contribute to both the observed reduced zero temperature ordered moment and the relatively large zero temperature spin susceptibility.…”