${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$: Magnetic and magnetotransport properties at ambient pressure and ferro- to antiferromagnetic transition under pressure

Transition-metal dichalcogenides (TMDCs) stand out with their high chemical stability and the possibility to incorporate a wide range of atoms and molecules between the layers. The behavior of conduction electrons in such $3d$-metal-inserted materials is closely related to their magnetic properties and can be sensitively controlled by external magnetic fields. Here, we study the magnetotransport properties of Mn-inserted $\mathrm{Nb}{\mathrm{S}}_2, {\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$, demonstrating a complex behavior of the magnetoresistance and of the ordinary and anomalous Hall resistivity. Application of high pressure as tuning parameter leads to the drastic changes of the magnetotransport properties of ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$ exhibiting large negative magnetoresistance up to $-65\%$ at 7.1 GPa. First-principles electronic structure calculations indicate a pressure-induced transition from a ferromagnetic to antiferromagnetic state. Theoretical calculations accounting for the finite temperature magnetic properties suggest a field-induced metamagnetic ferromagnetic-antiferromagnetic transition as an origin of the large negative magnetoresistance. These results inspire the development of materials for spintronic applications based on $3d$-element-inserted TMDCs with a well controllable metamagnetic transition.

Figure 1

Observed and calculated diffraction patterns for a sample of ${\mathrm{Mn}}_{0.25}\mathrm{Nb}{\mathrm{S}}_2$ for the set of (a) $hk0$ reflections and (b) $00l$ reflections. In the inset of panel (b) a representative rocking curve of the 002 reflection is presented.

Figure 2

Magnetic moment $M$ per formula unit of ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$. (a) $M_{\mathrm{OP}}$ for magnetic field along [0001]. The inset (b) shows the central part of minor loops up to $\pm 0.4\mathrm{T}$. (c) $M_{\mathrm{IP}}$ for field along [1000]. The inset (d) shows the strongly magnified central part of minor loops up to $\pm 0.2\mathrm{T}$. The inset (e) displays magnetic moment obtained during cooling in low fields of 50 and 100 mT for both the IP and OP direction. The data sets are of high density and are thus displayed as lines. Only in the two lower insets is the individual data shown as symbols.

Figure 3

Specific heat capacity $c_p/T$ of ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$ for zero and 9 T magnetic field. The inset shows the data in a $c_p/T$ vs $T^2$ representation at low temperatures.

Figure 4

Electrical resistivity obtained experimentally for ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$ at zero magnetic field, plotted as function of temperature for different pressure values.

Figure 5

Comparison of magnetization and magnetotransport behavior of ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$: (a) Derivative $d{M}_{\mathrm{OP}}/dH$ of the magnetization (field out-of-plane). (b), (c) Transverse (TMR) and longitudinal magnetoresistance (LMR) in percent. (d) Hall resistivity ${\rho }_{\mathrm{H}}\left({\mu }_{0}H\right)$. The dashed vertical lines mark characteristic changes with field for $T=2.0$, 50, and 100 K.

Figure 6

(a) Pressure evolution of Raman spectra and (b) pressure dependence of the frequencies of the observed Raman peaks.

Figure 7

Pressure- and temperature-dependent (a) transverse magnetoresistance and (b) Hall resistivity at $T=2\mathrm{K}$ for ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$ plotted as function of external magnetic field.

Figure 8

Total Bloch spectral function for ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$ under pressure for (a) $p=0$ and (b) 8.0 GPa. (c), (d) The Bloch spectral functions $A(k_y,k_z,E_F)$ (left) and $A(k_x,k_y,E_F)$ (right) at the Fermi level for $p=0$, for the majority-spin and minority-spin states, respectively; the BSF's $A(k_y,k_z,E_F)$ (left) and $A(k_x,k_y,E_F)$ (right) in panels (e) and (f) correspond to the majority- and minority-spin states, respectively, for 8.0 GPa.

Figure 9

(a) Pressure-dependent exchange interactions for ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$. Open symbols represent the results calculated for the FM reference states, closed symbols the AFM reference state. The MC results for the temperature-dependent magnetization $M\left(T\right)$ of ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$ for different pressure: $M\left(T\right)$ calculated for ${\mu }_{0}H=0$ (closed circles) and 4.0 T (open circles) at (b) $p=0.0$, (c) $p=8.0$ and (d) $p=9.0\mathrm{GPa}$. (e) Schematic representation of the total energy modification under pressure, plotted as a function of spin modulation characterized by period $\lambda$.

Figure 10

(a) The temperature-dependent magnetoresistance of ${\mathrm{Mn}}_{1/4}\mathrm{Nb}{\mathrm{S}}_2$: (a) Experimental results for the magnetic field of 9 T and the two pressures 0 and 7.1 GPa; (b) theoretical results for the magnetic field of 4 T used in the case of $p=0$ and 5 GPa. The results for $p=8\mathrm{GPa}$ are obtained using the resistivities for the FM and AFM states, TMR = $\left[\rho \right(T,\mathrm{FM})-\rho (T,\mathrm{AFM}\left)\right]/\rho (T,\mathrm{AFM})$.