PGGFlots 文本问题

Question

我正在尝试使用 TikZ 生成一些图，代码如下：

这与babel、、fontenc或无关inputenc；我曾尝试删除它们，但没有成功。

\documentclass[a4paper]{article}
\usepackage{pgfplots}
\usepackage[spanish]{babel}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\parindent=40pt
\begin{document}

\begin{tikzpicture}
    \begin{axis}[
        xlabel=$x$,
        ylabel=$y$]
    \addplot[smooth,mark=*,blue] plot coordinates {
        (0,2)
        (2,3)
        (3,1)
    };
    \addlegendentry{Case 1}

    \addplot[smooth,color=red,mark=x]
        plot coordinates {
            (0,0)
            (1,1)
            (2,1)
            (3,2)
        };
    \addlegendentry{Case 2}
    \end{axis}
    \end{tikzpicture}

\begin{tikzpicture}
    \begin{axis}
    [
        axis equal image,
        width = 5cm,
        height = 5cm,
        xmin=-1.0,xmax=10,
        ymin=-1.0,ymax=6,
        xlabel = {$f$},
        ylabel = {$I$},
        xtick = {0},
        xticklabels={},
        ytick = {0},
        yticklabels={},
        grid = none,
        axis x line=middle,
        axis y line=middle,
        clip=false,
        small,
    ]
    \draw[-] (axis cs:0,0) to [in=180,out=0] (axis cs:4,4) to [in=180,out=0] (axis cs:8,0);
    \draw[dashed] (axis cs:4,4) -- (axis cs:4,0) node [below] {$f_r$};
    \draw[dashed] (axis cs:4,4) -- (axis cs:0,4) node [left] {$\frac{V_s}{R}$};
    \end{axis}

\end{tikzpicture}


\end{document}

但我的结果将所有文本放在每个图的同一位置。