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Abstract:
Magnetization, P-31 nuclear magnetic resonance study, and
first-principles electronic structure calculations have been performed
in the spin-1 trimer chain compound CaNi3(P2O7)(2). Two separate spectra
arising from magnetically and crystallographically inequivalent P sites
are observed. In the ordered state, the resonance lines for both the P
sites (P1 and P2) are found to be split into two, which is clear
microscopic evidence of the development of two-sublattice AFM order
below T-M. A nonnegligible contribution of ferromagnetic hyperfine field
and dipolar field have also been seen in the ordered state. The
first-principles calculations show that the intratrimer (J(1)) and
intertrimer interactions (J(2)) are of weak ferromagnetic type with the
values 2.85 and 1.49 meV, respectively, whereas the interchain
interaction (J(3)) is of strong antiferromagnetic type with a value of
5.63 meV. The anisotropy of the imaginary part of dynamical spin
susceptibility around T-M along with the exponential decrement of 1/T-1
below T-M indicate the probable participation of the Ni-3d electron's
orbital degrees of freedom in the ferrimagnetic transition. The
dominance of orbital fluctuations over the spin fluctuations seems to be
responsible for showing low value of the binding energy u of the local
spin configuration (estimated from local spin models) and an unusually
weak exponent in the power-law behavior of 1/T-1 below 50 K, in the
paramagnetic state. Electronic structure calculations also reveal the
importance of orbital degrees of freedom of Ni-3d moments, which is
consistent with our NMR data analysis.
