Vector pulse magnet

Abstract

The underlying symmetry of the crystal, electronic structure, and magnetic structure manifests itself in the anisotropy of materials' properties, which is a central topic of the present condensed matter research. However, it demands such a considerable effort to fill the explorable space that only a small part has been conquered. We report a vector pulse magnet (VPM) as an alternative experimental technique to control the direction of applied magnetic fields, which may complement the conventional methods with its characteristic features. The VPM combines a conventional pulse magnet and a vector magnet. The VPM can create vector pulsed magnetic fields and swiftly rotating pulsed magnetic fields. As a demonstration, the three-dimensional magnetoresistance measurement of a highly oriented pyrolytic graphite is carried out using the AC four-probe method at 4.5 K and 6 T. The two-dimensional electronic structure of graphite is visualized in the three-dimensional magnetoresistance data. One can uncover the rotational and time-reversal symmetry of materials using a VPM and a variety of measurement techniques.

Figures (5)

• Figure 1: A schematic drawing of the VPM that can create a magnetic field in an arbitrary direction. The VPM is made of an inner coil and an outer coil. The inner and the outer coils are a mono-coil and a split-pair coil, respectively. One power supply is connected to the inner coil. The other power supply is connected to the outer split pair coil. The two electric circuits are independent, so one can trigger them with arbitrary delayed timing.
• Figure 2: (a) The trajectory of the generated vector pulsed magnetic field using a VPM plotted on the polar coordinates. The two insets show the magnetic field profiles generated by the inner coil $B_{z}$, and the outer coil $B_{x}$. Notice that two pulses are generated at the same time. The ratio of the magnetic field strength $B"/B'$ determines the direction $\theta$ of the generated magnetic field. The photo shows two orthogonal pickup coils for simultaneous measurements of $B_{x}$ and $B_{z}$. (b) The trajectory of the generated rotating pulsed magnetic field using a VPM plotted on the polar coordinates. The inset at bottom left shows the magnetic field profiles generated by the inner coil $B_{z}$, and the outer coil $B_{x}$. Notice that the pulses are shifted for $\pi/4$ in phase from each other. The inset at bottom right shows the profiles of $|B|$ and $\theta$ generated by the VPM.
• Figure 3: (a) The strength of the rotating magnetic field $|B| = \sqrt{B_z^{2} + B_{xy}^{2}}$ as a function of time, shown with the magnetic field profile of the inner coil $B_z$, and outer coil $B_{xy}$. (b) The angle of the rotating magnetic field $\theta = \tan^{-1}(B_{z}/B_{xy})$ as a function of time. (c) The $R_{xx}$ data of HOPG shown as a function of time measured using the AC four-probe method.
• Figure 4: (a) A schematic to show how to change $\phi$ by rotating the sample probe. (b) $R_{xx}(\theta, \phi, B)$ mapped in 3D space, where $B \simeq 6$ T for $0^{\circ}<\theta<90^{\circ}$ and $B< 6$ T for $90^{\circ}<\theta<180^{\circ}$. (c) Side view of the same data seen from $-x$ direction.
• Figure 5: (a) The data of $\Delta R_{xx}(\theta, \phi, B)/R_{xx}(0 {\rm\ T})$ mapped in the 3D space. Here, note that $B \simeq 6$ T for $0^{\circ}<\theta<90^{\circ}$ and $B< 6$ T for $90^{\circ}<\theta<180^{\circ}$. (b) The contour plot of the data in the $xy$ plane and (c) $zy$ plane. (d) The schematic drawings of the crystal structure and Fermi surface of graphite.