  We have generated an extended version of rather simplified but physically
oriented three-dimensional magnetar emission model, STEMS3D, to allow spectral
investigations up to 100 keV. We have then applied it to the broadband spectral
spectra of four magnetars: 4U 0142+61, 1E 1841-045, 1E 2259+586 and 1E
1048.1-5937, using data collected with Swift/XRT or XMM-Newton in soft X-rays,
and Nuclear Spectroscopic Telescope Array in the hard X-ray band. We found that
the hard X-ray emission of 4U 0142+61 was spectrally hard compared to the
earlier detections, indicating that the source was likely in a transition to or
from a harder state. We find that the surface properties of the four magnetars
are consistent with what we have obtained using only the soft X-ray data with
STEMS3D, implying that our physically motivated magnetar emission model is a
robust tool. Based on our broadband spectral investigations, we conclude that
resonant scattering of the surface photons in the magnetosphere alone cannot
account for the hard X-ray emission in magnetars; therefore, an additional
non-thermal process, or a population of relativistic electrons is required. We
also discuss the implication of the non-detection of persistent hard X-ray
emission in 1E 1048.1-5937.
