tikz two magnets and magnetic field

Question

I've adapted some tikz code I found for a different purpose to draw magnetic field lines between two magnets.

However, what I'd like is that the positions of the arrows on the lines line up in the correct fashion so that it looks less messy.

Also I'd love to have a current-carrying wire go through the middle of the two magnets, but I'm having a really hard time figuring out the coordinate system from this code.

When I plot \draw (0,0) -- (0,1) it draws a diagonal line rather than a straight line along the y-axis. Very strange.

\documentclass[]{scrartcl}
\usepackage{tikz}
\usetikzlibrary{arrows,3d,calc,intersections}
\usetikzlibrary{arrows,shapes,positioning}
\usetikzlibrary{decorations.markings}
\tikzstyle arrowstyle=[scale=1]
\tikzstyle directed=[postaction={decorate,decoration={markings,
    mark=at position .65 with {\arrow[arrowstyle]{stealth}}}}]
\tikzstyle reverse directed=[postaction={decorate,decoration={markings,
    mark=at position .65 with {\arrowreversed[arrowstyle]{stealth};}}}]

\begin{document}

\begin{tikzpicture}[x  = {(-0.65cm,-0.45cm)},
                    y  = {(0.65cm,-0.45cm)},
                    z  = {(0cm,0.8cm)},
                    scale = 2,
                    color = {lightgray}] 

% style of faces
\tikzset{facestyle/.style={shade,line join=round,
                           bottom color=darkgray!60,
                           top color=lightgray}}

\path (1.5,1.5,2) coordinate (c);  

% face "front or left" magnet 2
\begin{scope}[canvas is zy plane at x=-5]
  \path[facestyle] (-0.05,-4.5) rectangle (1.95,-2.5);  
\end{scope}  
% face arriere magnet 1
 \begin{scope}[canvas is zx plane at y=0]
   \path[facestyle] (5,4) rectangle (7,7);  
%   \draw[black] (6.98, -0.5) -- (6.98, 4);     
\end{scope}  
% face front magnet 1
\begin{scope}[canvas is zy plane at x=3]
  \path[facestyle] (2.5,-4) rectangle (0.5,-2);  
\end{scope}
% face sup magnet 1  
\begin{scope}
 \draw[facestyle]
       (1,-3,3.60) --  (1,-1,3.60) --  (4,-1,3.60) -- (4,-3,3.60);
 \draw[facestyle]  
       (-3.5,-3,3.60) --  (-3.5,-1,3.60) --  (-7,-1,3.60) -- (-7,-3,3.60) ; 
\end{scope}


<--------------------------- face right  magnet 2 --------------------> 
\begin{scope}[canvas is zx plane at y=2]
  \path[facestyle,opacity=.8] (5,-4) rectangle (7,-0.5); 
\end{scope}  
%<---------------------------rays of magnets  ------------------------>
\begin{scope}[canvas is zx plane at y=2]
  \path[facestyle] (5,4) rectangle (7,7);
  \draw[black, directed] (7,  -0.5) -- (7,  4);
       \draw[black, directed]        (5,  -0.5) -- (5,  4);
       \draw[black, directed]        (6,  -0.5) -- (6,  4);
       \draw[black, directed]        (5.5,-0.5) -- (5.5,4);
       \draw[black, directed]        (6.5,-0.5) -- (6.5,4) ;
              \draw[black, directed]        (7.0,-0.5) -- (7.0,4) ;
%
        \draw[black, directed]       (7.45,-.05)-- (7.45,4.45);

         \draw[black,directed]      (8.35,0.75) node[above right=1cm]{\textcolor{black!50}{NORTH}}%
            -- (8.35,5.25) node[below left=1cm]{\textcolor{black!50}{SOUTH}};
          \draw[black, directed]     (8.8,1.15) -- (8.8,5.65); 
 \end{scope}

%  \node[black,right] at (d)  {Alpha};
 \end{tikzpicture}   
\end{document}

Answer 1

Another option. This is a 3d one, with a \pic for the magnets.

\documentclass[tikz,border=2mm]{standalone}
\usetikzlibrary{3d,decorations.markings,perspective}
\tikzset
{
  pics/magnet/.style n args={4}{% magnet dimensions
      code={%
        \draw[pic actions,canvas is xy plane at z= #3] (-#1,-#2) rectangle (#1,#2);
        \draw[pic actions,canvas is yz plane at x=-#1] (-#2,0)   rectangle (#2,#3);
        \draw[pic actions,canvas is xz plane at y=-#2] (-#1,0)   rectangle (#1,#3);
        \path[draw=none] (-#1,0,#3) -- (#1,0,#3) node[midway,sloped,xslant=-0.6] {\strut#4};
    }},
  field/.style={%
      decoration={markings,mark=at position 0.6 with {\arrow{latex}}},
      postaction={decorate}
    },
}
\begin{document}
\begin{tikzpicture}[isometric view,line cap=round,line join=round]
% magnet dimensions
\def\x{0.9} % half
\def\y{0.6} % half
\def\z{1}
\def\s{2}   % separation between centers
% north magnet
\pic [fill=gray!80] at (\s,0,0) {magnet={\x}{\y}{\z}{north}};
% magnetic field
\foreach\i in {1,...,4} \foreach\j in {1,...,4}
  \pgfmathparse{25\j}
  \draw[red!\pgfmathresult,field] (\s-\x,{(2\i-5)\y/3},\z\j/3-\z/3) --++ (2\x-2\s,0,0);
% south magnet
\pic [fill=gray!80] at (-\s,0,0) {magnet={\x}{\y}{\z}{south}};
\end{tikzpicture}
\end{document}

Answer 2

Just stumbled over this old question. Maybe it is a little late and there are definitely better ways to draw cubes. Nevertheless it is one less unanswered question. Arrow style.

\documentclass[border=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{decorations.markings}
\pgfdeclarelayer{background}
\pgfdeclarelayer{foreground}
\pgfsetlayers{background,foreground}
\begin{document}
\tikzset{middlearrow/.style={
        decoration={markings,
            mark= at position 0.5 with {\arrow{#1}} ,
        },
        postaction={decorate},red,very thin
    }
}

\begin{tikzpicture}

\begin{pgfonlayer}{foreground}
    % cube 1
    \node[coordinate] at (0,1)(1){1};
    \node[coordinate] at (1,-1)(3){3};
    \node[coordinate] at (1,0)(2){2};
    \node[coordinate] at (-1,-2)(4){4};
    \node[coordinate] at (-2,-1)(5){5};
    \node[coordinate] at (-2,0)(6){6};
    \node[coordinate] at (-1,-1)(7){7};
    \node[] at (0,0.2)(S){\tiny SOUTH};

    % cube 2
    \node[coordinate] at (2,2)(8){1};
    \node[coordinate] at (3,0)(10){3};
    \node[coordinate] at (3,1)(9){2};
    \node[coordinate] at (2,1)(11){4};
    \node[coordinate] at (5,1)(12){5};
    \node[coordinate] at (5,2)(13){6};
    \node[coordinate] at (4,3)(14){7};
    \node[] at (3,1.75)(N){\tiny NORTH};

     %draw cube 1
    \draw[thick]  (1) to (2);
    \draw[thick]  (2) to (3);
    \draw[thick]  (3) to (4);
    \draw[thick]  (4) to (5);
    \draw[thick]  (5) to (6);
    \draw[thick]  (6) to (7);
    \draw[thick]  (7) to (4);
    \draw[thick]  (6) to (1);
    \draw[thick]  (7) to (2);

    \fill [gray,opacity=.5] (1.center) -- (2.center) -- (3.center) -- (4.center) -- (5.center) -- (6.center) --  cycle;

    %draw cube 2
    \draw[thick]  (8) to (9);
    \draw[thick]  (9) to (10);
    \draw[thick]  (10) to (11);
    \draw[thick]  (11) to (8);
    \draw[thick]  (12) to (13);
    \draw[thick]  (13) to (14);
    \draw[thick]  (10) to (12);
    \draw[thick]  (9) to (13);
    \draw[thick]  (8) to (14);

    \fill [gray,opacity=.5] (14.center) -- (13.center) -- (12.center) -- (10.center) -- (11.center) -- (8.center) --  cycle;
\end{pgfonlayer}

\begin{pgfonlayer}{background}
    % additional nodes for arrows
    \node[coordinate] at (3,0.8) (15){15};
    \node[coordinate] at (3,0.6) (16){16};
    \node[coordinate] at (3,0.4) (17){17};
    \node[coordinate] at (3,0.2) (18){18};
    \node[coordinate] at (1,-0.8) (181){181};
    \node[coordinate] at (1,-0.6) (171){171};
    \node[coordinate] at (1,-0.4) (161){161};
    \node[coordinate] at (1,-0.2) (151){151};

    \node[coordinate] at (2.7,1.3) (19){19};
    \node[coordinate] at (2.4,1.6) (20){20};
    \node[coordinate] at (0.7,0.3) (191){191};
    \node[coordinate] at (0.4,0.6) (201){201};

    % magnetic arrows
    \draw[middlearrow={stealth}] (8) -- (1);
    \draw[middlearrow={stealth}] (9) -- (2);
    \draw[middlearrow={stealth}] (10) -- (3);
    \draw[middlearrow={stealth}] (15) -- (151);
    \draw[middlearrow={stealth}] (16) -- (161);
    \draw[middlearrow={stealth}] (17) -- (171);
    \draw[middlearrow={stealth}] (18) -- (181);

    \draw[middlearrow={stealth}] (19) -- (191);
    \draw[middlearrow={stealth}] (20) -- (201);   

\end{pgfonlayer}
\end{tikzpicture}       


\end{document}