  A comprehensive study of selected properties of four (TiZrNbCu)_1-xNi_x (x
\le 0.25) amorphous high entropy alloys (a-HEA) has been performed. The samples
were ribbons about 20 \mum thick and their fully amorphous state was verified
by X-ray diffraction and thermal analysis. The surface morphology, precise
composition and the distribution of components were studied with a Scanning
electron microscope (SEM) with an energy dispersive spectroscopy (EDS)
attachment. The properties selected were the melting temperature (T_m), the low
temperature specific heat (LTSH), the magnetic susceptibility \chi_exp and the
Young^,s modulus (E). Whereas LTSH and \chi_exp were measured for the as-cast
samples, E was measured both for as-cast samples and relaxed samples (after a
short anneal close to the glass transition temperature). The LTSH showed that
the electronic density of states at the Fermi level, N_0(E_F), decreases with
increasing x, whereas the Debye temperature (\theta_D) increases with x. This
is similar to what is observed in binary and ternary amorphous alloys of early
transition metals (TE) with late transition metals (TL) and indicates that
N_0(E_F) is dominated by the d-electrons of the TE. The LTSH also showed the
absence of superconductivity down to 1.8K and indicated the emergence of the
Boson peak above 4K in all alloys.The free-electron like paramagnetic
contribution to \chi_exp also decreases with x, whereas E, like \theta_D,
increases with x, indicating enhanced interatomic bonding on addition of Ni.
The applicability of the rule of mixtures to these and other similar HEAs is
briefly discussed.
