Latency spikes in android when writting to file

I am running some performance tests and see some spikes in my tests results. This is the code I use to measure the time of the writing to file.

public class Test extends AndroidTestCase {

private DecimalFormat decimalFormat = new DecimalFormat("#.##");
private final Boolean isInternal = true;

public void testWrite() {
    Thread thread = new Thread() {
        public void run() {
            File dummy_file = createFile("dummy2", true);
            File file = createFile("normal_write", isInternal);
            for (int i = 0; i < 12500; i++) {
                long start = System.nanoTime();
                write(dummy_file, String.valueOf(i));
                long stop = System.nanoTime();
                double mSec = ((double) (stop - start) / 1000000.0);
                write(file, decimalFormat.format(mSec));
            }
        }
    };

    thread.start();

    try {
        thread.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

public File createFile(String fileName, Boolean isInternal) {
    deleteFile(fileName, isInternal);
    try {
        String file_path = "";
        if(isInternal == true) {
            file_path = getContext().getFilesDir().getAbsolutePath() + "/" + fileName + ".dat";
        } else {
            file_path = Environment.getExternalStorageDirectory() + "/" + fileName + ".dat";
        }
        File file = new File(file_path);
        file.createNewFile();
        FileWriter fw = new FileWriter(file.getAbsoluteFile(), true);
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write("##;##\n" +
                "@LiveGraph demo file.\n" +
                "Time");
        bw.newLine();
        bw.close();
        return file;
    } catch (IOException e) {
        e.printStackTrace();
    }
    return null;
}

public void deleteFile(String fileName, Boolean isInternal) {
    String file_path = "";
    if ( isInternal == true) {
        file_path = getContext().getFilesDir().getAbsolutePath() + "/" + fileName + ".dat";
    } else {
        file_path = Environment.getExternalStorageDirectory() + "/" + fileName + ".dat";
    }
    File file = new File(file_path);
    file.delete();
}

public void write(File file, String content) {
    try {
        FileWriter fw = new FileWriter(file.getAbsoluteFile(), true);
        BufferedWriter bw = new BufferedWriter(fw);
        bw.write(content);
        bw.newLine();
        bw.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

}

Mostly the time it takes to write is ~0.1-0.2ms but there are spikes which takes 10+ ms and can not figure out what the cause of this is. I can not link the graph here right now as I am a new user here.

I am really stuck with this any ideas?.