When was yibum stopped from ashkenazi tradition and why? Until when it was practiced among the sephardic jews? If a brother in law marries wants to marry his widowed sister in law, because he loves her and not for the sake of "perpetuating the name of the dead", is such a marriage acceptable by halacha?

The Mishna in Bechorot 13a (See also Ketuvot 64a) discusses the preference of Yibum or Chalitza and already in their time brought up the issue of intentions "leshem Shamayim" or ulterior motives for Yibum in which case Chalitza should be preferrred. The reason for forbidding Yibum other than the intention dictated by the Torah is because it removes the special permission of marrying a brother's wife which under normal circumstances would be considered "erva" and be forbidden. (See Yebamoth 39b) The issue of preference of Yibum or Chalitza is a lengthy debate among the Geonim and Rishonim. (See Talmudic Encyclopedia Vol. 21 under entry of Yibum for a summary. ) The Shulchan Aruch (Even Haezer 165: a) follows the opinion of the Rif and Rambam who say thar Yibum is preferred over Chalitza while the Rema seems to say otherwise. The Aruch Hashulchan (Even Ha'ezer 165:15 ) says that the minhag among Ashkenzim has been to prefer Chalitza over Yibum while the Sefardi custom has been the opposite. The Chief Rabbinate of Israel , under the leadership of Rabbi Hertzog zt"l and Rav Uziel in 1950, made an ordinance of uniformity for Askenzim and Sfardim that chalitza is to be preferred.