Suppressed magnetic order and non-Fermi-liquid behavior in MnSi thin films under hydrostatic pressure

In MnSi thin films the magnetic properties of the B20 compound are influenced by induced uniaxial anisotropy. In comparison to bulk MnSi the critical magnetic fields are enhanced and the Skyrmion phase is found to be enlarged within the magnetic phase diagram. Furthermore the ordering temperature depends on the film thickness reaching 43 K for films of around 10 nm and is considerably higher than in bulk crystals ($T_{c,\mathrm{bulk}}=29$ K). In bulk MnSi the ordering temperature can be reduced by pressure, where at 1.46 GPa the magnetic order is completely suppressed and a non-Fermi-liquid behavior characterized by a $T^{3/2}$ law of the resistivity is observed. We present resistance measurements on MnSi thin films under applied pressure of up to 3.44 GPa. Qualitatively, the behavior is similar to bulk MnSi. However, the critical pressure is considerably enhanced to 3.1 GPa, which is assumed to be a consequence of strain. At high pressure non-Fermi-liquid behavior evidenced by a $T^{3/2}$ behavior of the resistance is observed up to $T_{\mathrm{lin}}=30$ K, i. e., in a larger temperature range than for bulk MnSi. Uniaxial anisotropy might play an important role in this breakdown of Fermi-liquid behavior, since it stabilizes nontrivial spin structures.

Figure 1

Normalized electrical resistance $R/R_{2K}$ vs temperature for a 9 nm film MnSi under hydrostatic pressure.

Figure 2

Temperature-pressure phase diagram for the MnSi thin film. Round and square symbols mark the values of $T_{\mathrm{ord}}$ and $T_{\mathrm{lin}}$ (see text), respectively. The lines are guides for the eye.

Figure 3

Temperature derivative of the resistance curves for pressures around 3.1 GPa. For $p<3.1$ GPa a steep decrease marked by arrows defines $T_{\mathrm{ord}}$. Above 3.1 GPa this feature vanishes.

Figure 4

Pressure dependence of the exponent $n$ in $R=R_0+A{T}^n$ defined by the logarithmic derivative of $(R-R_0)$ at low temperatures. The insets show the temperature dependence of $d$ ln$(R-R_0)/d$ ln $T$ for $p=0$ GPa (left) and 3.20 GPa (right).

Figure 5

Comparison of the pressure dependence of $T_{\mathrm{ord}}$ in thin film and bulk MnSi. Bulk values were taken from Refs. [4, 5].