High pressure electrical resistivity and specific heat of the heavy fermion compound CeCoGe_2.2Si_0.8

Abstract

We study the evolution of the magnetic ground state close to the putative quantum critical point in CeCoGe 2.2 Si 0.8 by using electrical resistivity and specific heat measurements under the same high hydrostatic pressure conditions. The electrical resistivity shows that the antiferromagnetic ordering temperature, T N , is suppressed above P C ¼ 5.9 kbar, with the emergence of non-Fermi liquid behavior. On the other hand, the specific heat shows two different magnetic transitions at 0 kbar, one at T N and another one at T l % 0.3 K. Both transition temperatures are reduced by pressure but remain finite up to at least 7.2 kbar. The height of the specific heat anomaly at T N , DC N , is strongly reduced above P C . These features suggest that the quantum criticality in CeCoGe 2.2 Si 0.8 is governed by disorder.1 Introduction Investigations of the role that disorder plays in strongly correlated electron materials close to a quantum critical point (QCP) have awaken a lot of interest during the last decade [1][2][3][4]. An open issue [5] is to understand how for systems with translational invariant symmetry disorder changes the universal quantum criticality and the low-lying energy scales that emerge in the vicinity of the phase transition at T ¼ 0 K. The pseudo-ternary heavy fermion (HF) system CeCoGe 3-x Si x [6] with tetragonal BaNiSn 3 -type structure and antiferromagnetic (AF) order between 0.5 < x 1 has been claimed to be dominated by the disordered Griffiths phase at its doping-induced QCP [7]. A recent investigation using electrical resistivity, r(T), under hydrostatic high pressure, P, on the AF HF compound x ¼ 0.9 [8] has revealed that the P-tuned QCP (P C ¼ 6.2 kbar) is dominated by different effects on both sides of the QCP: on the magnetic side spin fluctuations govern the criticality, while on the non-magnetic side the criticality is dominated by disorder that quenches the spin fluctuations. More recently, we have performed DC-magnetic susceptibility, x(T), measurements under high P on a sample with x ¼ 0.8 [9], a composition close to that reported in previous r(T) measurements. Our results suggested that a spin glass-like

Converse effect of pressure on the quadrupolar and magnetic transition inCe3Pd20Si6

“…4(c). As the size of ρ N /ρ 0 is generally considered to be a measure of the strength of the AF order [1,11,24,26,27], its increase with pressure confirms that pressure stabilizes the AF order, at least up to 6.2 kbars. To determine the pressure-magnetic field-temperature phase diagram, isothermal magnetoresistance (MR) measurements were done at different pressures (Fig.…”

“…3). As the size of ∆ρ N /ρ 0 is generally considered to be a measure of the strength of the AF order [1,11,24,26,27], its increase with pressure confirms that pressure stabilizes the AF order, at least up to 6.2 kbar.…”

“…The sample modulation temperature was read out by a lock-in amplifier in a second harmonic mode and recorded as pick-up voltage (V ac ). The inverse of this quantity is approximately proportional to the sample's specific heat [24]. The sample temperature was corrected for a DC offset due to Joule heating by separately measuring the temperature signal with a DC nanovoltmeter.…”

Complex magnetism and non-Fermi liquid state in the vicinity of the quantum critical point in the CeCo$_{1-x}$Fe$_x$Ge$_3$ series

“…43,44 Adding a small amount of Si in the place of Ge leads to even a more complex magnetic structures. [45][46][47] CeFeGe 3 is a paramagnet with a high Kondo temperature (over 100 K) 48,49 . Substituting cobalt with iron and creating the CeCo 1−x Fe x Ge 3 alloys series is expected to compensate magnetic ordering of CeCoGe 3 at QCP.…”