Insert JSON data to file with Laravel

I am inserting JSON data to a file with Laravel, I have 300 000 records and I want to insert them by block of 5000 records.

 public function fileput($start,$end,$n) {
        $final = [];
        $res = DB::table('company')
                ->Where('company_id', '>',$start)
                ->Where('company_id', '<',$end)
                ->get();

        foreach ($res as $k => $v) {
            $id = $v->company_id;
            $index = 10000000 + $id;
            unset($res[$k]->company_id);
            unset($res[$k]->company_data);
            $arr = array('index' => ['_id' => $index]);
            $ind = json_encode($arr);
            $data = json_encode($v);
            array_push($final, $ind, $data);
        }
        $written = File::put('file.txt', $final);
} 

Problem is, after entering first 5000, when incrementing to 10000, first 5000 records got erased.

Therefore how can I insert all the records in one file?