Pressure-induced suppression of ferromagnetism in ${\mathrm{CePd}}_2{\mathrm{P}}_2$

The correlated electron material ${\mathrm{CePd}}_2{\mathrm{P}}_2$ crystallizes in the ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure and orders ferromagnetically at 29 K. Prior work by Lai et al. [Phys. Rev. B 97, 224406 (2018)] found evidence for a ferromagnetic quantum critical point induced by chemical compression via substitution of Ni for Pd. However, disorder effects due to the chemical substitution interfere with a simple analysis of the possible critical behavior. In the present paper, we examine the temperature—pressure—magnetic-field phase diagram of single crystalline ${\mathrm{CePd}}_2{\mathrm{P}}_2$ to 25 GPa using a combination of resistivity, magnetic susceptibility, and x-ray diffraction measurements. We find that the ferromagnetism appears to be destroyed near 12 GPa, without any change in the crystal structure.

Figure 1

The left panel shows the PM-FM transition of ${\mathrm{CePd}}_2{\mathrm{P}}_2$ in the real part of the AC magnetic susceptibility at various pressures. Note that as pressure increases, the transition temperature decreases, as does the size of the transition. At 10.0 Gpa and above, the transition becomes undetectable in $\chi$. The transition temperature was defined as the inflection point, as determined by the second derivative of the real part of the magnetic susceptibility and is indicated by arrows on each curve. The right panel shows the second derivative of the real part of the AC magnetic susceptibility for each transition. In both plots, data are offset for clarity.

Figure 2

Resistivity as a function of temperature for ${\mathrm{CePd}}_2{\mathrm{P}}_2$ run A at pressures below 12 GPa (left) and above (right). Above 12 GPa, the transition temperature can not be accurately determined.

Figure 3

Resistivity as a function of temperature for ${\mathrm{CePd}}_2{\mathrm{P}}_2$ run B at pressures below 12GPa (left) and above (right), showing resistivity behavior up to 180K.

Figure 4

Resistivity as a function of pressure for ${\mathrm{CePd}}_2{\mathrm{P}}_2$. Note the resistivity peak near 12 GPa, close to the pressure where the transition disappears in $\chi$ and $\rho$.

Figure 5

Magnetoresistance as a function of temperature for ${\mathrm{CePd}}_2{\mathrm{P}}_2$ at varying pressures. At low pressure, magnetoresistance is negative and possesses a clear valley near the transition temperature for a given pressure. Above about 12 GPa, however, this feature vanishes, and as pressure increases further, magnetoresistance shifts from negative to positive above about 13.4 GPa. The inset shows magnetoresistance of ${\mathrm{CePd}}_2{\mathrm{P}}_2$ as a function of pressure at 6 K and 25 K. At 25 K, above $T_C$, magnetoresistance starts negative and gradually increases, becoming positive at higher pressures. The 6 K data shows a deep minimum at 11.7 GPa, near the critical pressure where the magnetic order appears to vanish.

Figure 6

XRD patterns for ${\mathrm{CePd}}_2{\mathrm{P}}_2$ at various pressures. Pressure increases with increasing height, beginning at about 1 GPa and increasing to a maximum of about 30 GPa. No structural transition is observed within this pressure range.

Figure 7

Unit cell volume versus pressure, obtained by x-ray diffraction. The Vinet equation was fitted to the data to obtain the bulk modulus. The inset shows the ratio of lattice constants $c/a$ as a function of pressure. The $c/a$ ratio increases with pressure, suggesting that ${\mathrm{CePd}}_2{\mathrm{P}}_2$ exhibits substantially three-dimensional bonding. The increased scatter at around 7.4 GPa may be due to the freezing of the pressure medium. Error bars are approximately the size of the symbols shown.

Figure 8

Phase diagram showing the ferromagnetic transition temperature of ${\mathrm{CePd}}_2{\mathrm{P}}_2$ versus pressure. The orange line represents a linear fit to this data and the vertical blue line indicates the pressure at which the resistivity peaked as a function of pressure.

Figure 9

Critical temperature as a function of volume for ${\mathrm{CePd}}_2{\mathrm{P}}_2$ and $\mathrm{Ce}{(\mathrm{Ni},\mathrm{Pd})}_2{\mathrm{P}}_2$. The filled symbols represent high-pressure data on ${\mathrm{CePd}}_2{\mathrm{P}}_2$, while the open symbols correspond to lattice constants for $\mathrm{Ce}{(\mathrm{Ni},\mathrm{Pd})}_2{\mathrm{P}}_2$ from Ref. [22]. The magnetic transition is suppressed by chemical and mechanical compression at different rates, though both decrease roughly linearly. Despite a large difference in $T_C$, the magnetic transition becomes undetectable at the same critical volume.