Magnetic field dependence of the non-Fermi-liquid state in ferromagnetic CePd1-xNix

Article abstract of DOI:10.1016/j.jmmm.2003.12.604

The results of measurements of the electrical resistivity (ρ), specific heat (C), and magnetic susceptibility (χ) are reported for compounds near the ferromagnetic transition in the CePd_1-xNi _x system. The magnetoresistance is large

Full text of DOI:10.1016/j.jmmm.2003.12.604

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 207–208
Magnetic field dependence of the non-Fermi-liquid state in
ferromagnetic CePd1ꢀxNix
A.M. Strydoma,*, G. Bonfaitb,c, I. Catarinob,c, L. Pereirac, P. de V. du Plessisd
a Physics Department, Rand Afrikaans University, PO Box 524, Auckland Park 2006, JHB, South Africa
b Physics Deptartment, FCT-UNL, Caparica 2829-516, Portugal
c
!
Chemistry Department, ITN, Sacavem 2856, Portugal
d School of Physics, University of the Witwatersrand, PO WITS 2050, JHB, South Africa
Abstract
The results of measurements of the electrical resistivity ðrÞ; specific heat ðCÞ; and magnetic susceptibility ðwÞ are
reported for compounds near the ferromagnetic transition in the CePd1ꢀxNix system. The magnetoresistance is large
and positive at low temperatures. The zero-field non-Fermi-liquid characteristics of rðTÞ and of CðTÞ are shown to be
modified in an applied field.
r 2003 Elsevier B.V. All rights reserved.
PACS: 72.15.Gd; 75.20.Hr; 75.40.Cx
Keywords: CePd1ꢀxNix; Non-Fermi-liquid; Magnetoresistivity; Magnetic susceptibility; Specific heat
The pseudobinary CePd1ꢀxNix system shows interest-
ing non-Fermi-liquid behaviour [1]. The parent com-
pound CePd orders into the ferromagnetic state at
T ¼ 6:6 K [2] with a high-temperature effective mag-
netic moment of 2:50 mB which is very close to the full
Hund’s rule 4f-configuration moment value. On the
other hand, CeNi shows clear thermodynamic and
transport characteristics of an intermediate valent (IV)
metal [3]. In CePd1ꢀxNix; the orthorhombic CrB-type
structure was found to persist throughout the entire
concentration range [2]. Since Pd and Ni are approxi-
mately isoelectronic d-electron metals, their systematic
substitution in CePd1ꢀxNix can be expected to represent
a controlled variation in the cerium interionic distance.
The sensitive balance between the IV state and the FM
state was shown [3] to lead to a narrow concentration
range that displays non-Fermi-liquid (nFL) behaviour.
In the present study we report on measurements to
investigate the magnetic field dependence of the nFL
state of CePd1ꢀxNix: Samples with 0:92pxp0:955;
together with LaNi were prepared by arc-melting of
stoichiometric quantities of Ce, La, and Pd ð99:99 wt%Þ
and Ni ð99:95 wt%Þ in an ultrahigh-purity argon atmo-
sphere. No further heat treatment was given. The
samples were all checked using powder X-ray diffraction
and verified to have formed in the expected crystal
structure, free from parasitic phases and unreacted
material.
Fig. 1 shows the temperature dependence of the
magnetic susceptibility, wðTÞ; for several compounds in
the CePd1ꢀxNix system. The data are plotted against
T0:75 to emphasize the development of a power-law
below B5 K for compounds near the critical point.
Measurements of wðT; BÞ are needed at lower tempera-
tures in order to investigate the possible extension of this
observed power-law behaviour. Fig. 2 shows the main
features of the temperature dependence of the cerium
4f-electron electrical resistivity, r4f ðT; BÞ that is
obtained by subtracting rLaNiðT; BÞ from the measured
rðT; BÞ data, for various values of applied field on
CePd0:06Ni0:94: Nieva et al. [2] indicated ferromagnetic
ordering for their 6% Pd compound, while in our series
of compounds CePd0:06Ni0:94 was found to be the
highest Pd concentration that did not show any anomaly
*Corresponding author. Tel.: +27-11-489-2320; fax: +27-
11-489-2339.
E-mail address: ams@na.rau.ac.za (A.M. Strydom).
0304-8853/$ - see front matter r 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2003.12.604

ARTICLE IN PRESS
A.M. Strydom et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 207–208
208
Fig. 3. Specific heat data vs. temperature for various applied
fields. The values of C=ðT ¼ 2 KÞ are plotted in the inset to
illustrate the evolution with field.
Fig. 1. Magnetic susceptibility vs. T0:75 for various CePd1ꢀxNix
compounds. The straight line is a guide to the eye.
isofield curves between zero field and B ¼ 16 T: The
inset to Fig. 2 plots the steady increase of the n-exponent
with field. For high fields, the exponent reaches
n ¼ 1:55ð1Þ; a value which is close to the rBT5=3
behaviour predicted for rðTÞ very near the ferromag-
netic transition [4]. This supports an interpretation of
the applied field inducing ferromagnetic spin alignment.
In Fig. 3 specific heat data are plotted in the main
figure on semi-log axes to reveal the C=TBln T
behaviour in zero field, as was also found by Kappler
et al. [1]. The applied magnetic field is mainly found to
cause a suppression of the low-temperature enhance-
ment of C=T; which is probably due to the magnetic
field lifting the strongly correlated spin degeneracy. As a
result, the B ¼ 12 T data of C=T enters near-saturation
towards low temperatures, which could be reconciled
with a Fermi-liquid ground state. The inset of Fig. 3
illustrates the E30% decrease in the C=ðT ¼ 2 KÞ
measured values when applying a field of B ¼ 12 T:
Fig. 2. Electrical resistivity vs. temperature. The solid lines
represent least-squares fits to the data (see text) the temperature
exponent of which is plotted in the inset against applied field.
in AC-susceptibility data down to 1:78 K (not shown),
and hence we analyze this particular compound as being
just at the edge of a ferromagnetic transition. We note
that the r values are increased by an applied field,
indicating an anomalous positive magnetoresistivity
(MR) for this system. Weak and nearly ferromagnetic
metals are expected to show negative MR, in response
to suppression of spin fluctuations [4]. There is a
clear evolution seen in the power-law dependence,
rðTt10 KÞ ¼ r0 þ ATn (see solid lines in Fig. 2) for
References
[1] J.-P. Kappler, et al., Physica B 230–232 (1997) 162.
[2] G.L. Nieva, et al., Z. Phys. B: Condens. Matter 70 (1988)
181.
[3] D. Gignoux, et al., J. Less-Common Met. 94 (1983) 165.
[4] T. Moriya, Spin Fluctuations in Itinerant Electron Magnet-
ism, Springer, Berlin, 1985.