Fermi surface and interlayer transport in the two-dimensional magnetic organic conductor (Me-3,5-DIP)[Ni(dmit)${}_2$]${}_2$

Resistance and magnetic torque measurements at low temperatures under high magnetic fields have been performed for a magnetic organic conductor (Me-3,5-DIP)[Ni(dmit)${}_2$]${}_2$ to investigate the electronic state. This conductor contains two types of Ni(dmit)${}_2$]${}_2$ anion layers, layers I and II. Shubnikov-de Haas and angular-dependent magnetoresistance oscillations clearly show that there exists a two-dimensional Fermi surface in layer II, whose spins are strongly coupled with the localized spins in layer I. When the magnetic field is applied parallel to the layers, the interlayer resistance shows a sharp minimum at $~8$ T and then slow oscillation at higher fields. The minimum is explained by the combined effect of the field-dependent magnetic potential and momentum shift in the interlayer tunneling. The mechanism of the slow oscillation is not clarified yet.

Figure 1

(a) Crystal structure of (Me-3,5-DIP) [Ni (dmit)${}_2$]${}_2$. (b) The first Brillouin zone and the Fermi surface in layer II obtained by the band-structure calculation. ${{\mathit{a}}_p}^{*}$ and ${{\mathit{b}}_p}^{*}$ show the reciprocal lattice vectors of the primitive cell. The unit vectors of the primitive cell are taken as ${\mathit{a}}_p=(\mathit{a}+\mathit{b})/2$ and ${\mathit{b}}_p=\mathit{b}$ (from Ref. 14).

Figure 2

Temperature dependence of the $c$-axis resistance under magnetic fields for $H\parallel c^{*}$, perpendicular to both $a$ and $b$ axes.

Figure 3

AMRO measurements at various fields for (a) $\varphi =0^{°}$ and (b) $\varphi =90{}^{ˆ}$ Inset: Definition of the magnetic field angles $\theta$ and $\varphi$.

Figure 4

(a) The second derivative curves of the AMRO data at 14 T. Peaks isolated from the periodic ones are denoted by arrows. The triangle for $\varphi =0$ indicates a missing peak for some reason. (b) Polar plot of $k_{\parallel }$. The ellipsoid (solid curve) shows the cross section of the 2D Fermi surface.

Figure 5

The resistance in magnetic field perpendicular to the conduction layers. Insets: Closeup of the SdH oscillation at $~15$ T and the Fourier transform spectrum of the oscillation between 8 and 18 T.

Figure 6

(a) The field dependence of the resistance at various angles. Each curve is shifted for clarity. (b) The magnetic field angle dependence of the SdH oscillation frequencies obtained from the SdH oscillations shown in (a). The solid lines show $1/\cos \theta$ dependences expected for the 2D Fermi surface.

Figure 7

(a) Resistance as a function of magnetic field. Each curve is shifted for clarity. (b) The second derivative curve of the resistance vs the inverse field. (c) The magnetic field angle dependence of the oscillation frequency. The solid line shows $16/\cos \theta$ (T).

Figure 8

High-field interlayer resistance for a different sample from the same batch. (a) Resistance at various field angles. (b) Resistance at various temperatures.

Figure 9

Magnetic torque as a function of the field angle $\theta$ at various magnetic fields for (a) $H$ in the $c^{*}b$ plane and (b) $H$ in the $c^{*}a$ plane.

Figure 10

(a) Magnetic torque divided by field as a function of field. (b) Oscillatory part (dHvA oscillations) of the data shown in (a). (c) The FT spectra of the dHvA oscillations.

Figure 11

Peak-to-peak amplitude and the peak angle of the torque curve as a function of temperature for (a) $H$ in the $c^{*}b$ plane and (b) $H$ in the $c^{*}a$ plane.

Figure 12

Schematic interpretation of the resistance minimum in parallel fields.