Abstract:
We present magnetization, specific heat, and
27
Al
NMR investigations on
YbFe
2
Al
10
over a wide range in temperature and magnetic field. The magnetic susceptibility at low temperatures is strongly enhanced at weak magnetic fields, accompanied by a
ln
(
T
0
/
T
)
divergence of the low-
T
specific heat coefficient in zero field, which indicates a ground state of correlated electrons. From our hard-x-ray photoemission spectroscopy study, the Yb valence at 50 K is evaluated to be 2.38. The system displays valence fluctuating behavior in the low to intermediate temperature range, whereas above 400 K,
Yb
3
+
carries a full and stable moment, and Fe carries a moment of about
3.1
μ
B
. The enhanced value of the Sommerfeld-Wilson ratio and the dynamic scaling of the spin-lattice relaxation rate divided by
T
[
27
(
1
/
T
1
T
)
]
with static susceptibility suggests admixed ferromagnetic correlations.
27
(
1
/
T
1
T
)
simultaneously tracks the valence fluctuations from the
4
f
Yb ions in the high temperature range and field dependent antiferromagnetic correlations among partially Kondo screened Fe
3
d
moments at low temperature; the latter evolve out of an Yb
4
f
admixed conduction band.
DOI: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.216403