Pressure-induced Magnetic Transition in a Single Crystal of YbCo₂Zn₂₀

Abstract

We have measured the electrical resistivity of a single crystal of YbCo 2 Zn 20 at pressures up to 2.37 GPa and at temperatures from 50 mK to 300 K. Above a critical pressure P c ($ 1 GPa), we have found a resistivity anomaly at T M ($ 0:15 K at 1 GPa) that increases with the pressure. At the ambient pressure, the system shows a nonmagnetic ground state described by the Fermi-liquid model. The T 2 coefficient of the electrical resistivity A strongly increases with the pressure upon approaching P c . However, in the vicinity of P c , the temperature dependence of the resistivity deviates from the Fermiliquid description. These observations suggest that the application of hydrostatic pressure induces a magnetically ordered state for P ! P c and T T M .In intermetallic compounds, including Ce and Yb, the hybridization between the 4f and itinerant conduction-band electrons induces the instability of magnetic moments and charge configurations. In recent years, one of the most interesting topics is the ground state properties of heavy fermion metals located at or close to a magnetic quantum critical point (QCP). 1) The application of external pressure is one of the important tools for controlling the electronic configurations as well as chemical pressure. In the case of heavy fermion Ce compounds exhibiting antiferromagnetic order, such as CeIn 3 and CePd 2 Si 2 , 2) the magnetic order is suppressed by applying pressure. Interestingly, unconventional superconductivity appears in the vicinity of the QCP at which the magnetic ordering temperature is decreased to zero.So far, pressure-induced magnetic transitions have been observed in some Yb-based compounds. [3][4][5][6][7] The key point here is that Yb ions fluctuate between the nonmagnetic Yb 2þ (J ¼ 0) and the magnetic Yb 3þ (J ¼ 7=2) states. Since the ionic volume of the magnetic Yb 3þ state is smaller than that of the nonmagnetic Yb 2þ one, applying pressure stabilizes the magnetic Yb 3þ configuration and induces the appearance of a magnetically ordered state in contrast to the Ce case. However, the critical pressure for these compounds is as high as or higher than 6 GPa, which prevents us from understanding the physics in the vicinity of the magnetic QCP because of difficulties in high-pressure experiments.The series of compounds YbT 2 Zn 20 (T = Fe, Co, Ru, Rh, Or, Ir) belongs to a new heavy fermion system crystallizing in the cubic CeCr 2 Al 20 structure. 8,9) All these compounds show an enhanced Sommerfeld coefficient of the specific heat exceeding 400 mJ/(mol K 2 ). The high-temperature magnetic susceptibility of these compounds follows the Curie-Weiss law with the effective moments close to the value for the free Yb 3þ ion ( eff ¼ 4:54 B ), although there is no indication of magnetic order down to 20 mK. In the YbT 2 Zn 20 family, YbCo 2 Zn 20 exhibits some notable features as follows. The low temperature electrical resistivity and specific heat can be described by the formulas ¼ 0 þ AT 2 and C=T ¼ constant, as expected from the Fermiliquid behavior; the value...

Thermal and magnetic properties of the low-temperature antiferromagnetCe4Pt12Sn25

“…Ce-based filled skutterudites CeT 4 X 12 ͑T = Fe, Ru, Os; X = P, As, Sb, d Ce-Ce ϳ 7 Å͒ form one of these families, with most members semiconducting with the gap size that correlates with the lattice constant. 19 Another example is a family of Yb-based HF compounds YbA 2 Zn 20 ͑A = Fe, Co, Ru, Rh, Os, Ir, d Yb-Yb ϳ 6 Å͒, [20][21][22] where the Kondo physics appears to dominate the RKKY interaction, in accord with the simple argument above.…”

NMR Studies of Yb-Based Heavy Fermion Compound YbCo2Zn20

“…Single crystal samples of YbCo 2 Zn 20 were grown using the Zn self-flux method as reported previously [2]. Some pieces of them were ground into powder with a typical grain size of a few hundred microns.…”

“…Besides, electrical resistivity and specific heat measurements under pressure suggest a nonmagnetic-magnetic transition with low critical pressure of ∼ 1 GPa [2,3], which implies that this compound locates very close to the magnetic instability at ambient pressure. Recently, magnetoresistance and magnetization measurements have shown anomalously large magnetic field effect on this compound, which brought new interest of this compound, including rapid decreases in cyclotron effective mass and in T 2 coefficient A of resistivity with increasing field, metamagnetic like anomaly, and a new field-induced ordered phase [4][5][6].…”

Field-Induced Order in Heavy-Fermion Compound YbCo2Zn20

“…In fact, YbCo 2 Zn 20 reacts sensitively against external fields. Relatively small pressure of ∼1 GPa is sufficient to induce an ordered state with T M =0.15 K, which increases with pressure [3]. Single crystal neutron scattering experiments under pressure confirmed that an antiferromagnetic peak is induced at (1 0 0) in the pressure-induced ordered state [4].…”