Two-channel optical bistability and multistability in a degenerate four-level atomic medium under a static magnetic field oleh Nguyen Thi Thu Hien, Nguyen Linh Dan, Nguyen Huy Bang, Dinh Xuan Khoa, Nguyen Van Phu, Nguyen Thi Lan Anh, Mai Thi Thu Huong, Luong Thi Cam Nhung, Tran Thi Truc Linh, Le Thi Thuy, Nguyen Thi Yen Chau, Le Nguyen Mai Anh, Le Van Doai