  The thermodynamic properties of the pyrochlore Yb2Ti2O7 material are
calculated using the numericallinked-cluster (NLC) calculation method for an
effective anisotropic-exchange spin-1/2 Hamiltonian with parameters recently
determined by fitting the neutron scattering spin wave data obtained at high
magnetic field h. Magnetization, M(T,h), as a function of temperature T and for
different magnetic fields h applied along the three high symmetry directions
[100], [110] and [111], are compared with experimental measurements on the
material for temperature T>1.8K. The excellent agreement between experimentally
measured and calculated M(T,h) over the entire temperature and magnetic field
range considered provides strong quantitative validation of the effective
Hamiltonian. It also confirms that fitting the high-field neutron spin wave
spectra in the polarized paramagnetic state is an excellent method for
determining the microscopic exchange constants of rare-earth insulating magnets
that are described by an effective spin-1/2 Hamiltonian. Finally, we present
results which demonstrate that a recent analysis of the polarized neutron
scattering intensity of Yb2Ti2O7 using a random phase approximation (RPA)
method [Chang et al., Nature Communications {3}, 992 (2012)] does not provide a
good description of M(T,h) for $T\lesssim 10$ K, that is in the entire
temperature regime where correlations become non-negligible.
