...since Hama bore off
to the shining city the Brosings' necklace,
Gem-figured filigree. He gained the hatred
Of Eormanric the Goth, chose eternal reward.
This seems to confuse two different stories as the Beowulf poet is clearly referring to the Dietrich Cycle. The Þiðrekssaga tells that the warrior Heime (Hama in Old English) takes sides against Eormanric, king of the Goths, and has to flee his kingdom after robbing him; later in life, Hama enters a monastery and gives them all his stolen treasure. However, this saga makes no mention of the great necklace. Possibly the Beowulf poet was confused, or invented the addition of the necklace to give him an excuse to drag in a mention of Eormanric. In any case, the necklace given to Beowulf in the story is not the Brísingamen itself; it's only being compared to it.
This myth is also recorded in a Swedish folksong called the Thor song (18th Century), where Freyja is called Miss Frojenborg, "den väna solen" (the fair sun).
Snorri Sturluson quoted this old poem in Skáldskaparmál, saying that because of this legend Heimdall is called "Seeker of Freyja's Necklace" (Skáldskaparmál, section 8) and Loki is called "Thief of Brísingamen" (Skáldskaparmál, section 16). A similar story appears in the later Sörla þáttr, where Heimdall does not appear.
"Freyja was a human in Asia and was the favorite concubine of Odin, King of Asialand. When this woman wanted to buy a golden necklace (no name given) forged by four dwarves (named Dvalinn, Alfrik, Berling, and Grer), she offered them gold and silver but they replied that they would only sell it to her if she would lie a night by each of them. She came home afterward with the necklace and kept silent as if nothing happened. But a man called Loki somehow knew it, and came to tell Odin. King Odin commanded Loki to steal the necklace, so Loki turned into a fly to sneak into Freyja's bower and stole it. When Freyja found her necklace missing, she came to ask king Odin. In exchange for it, Odin ordered her to make two kings, each served by twenty kings, fight forever unless some christened men so brave would dare to enter the battle and slay them. She said yes, and got that necklace back. Under the spell, king Högni and king Heðinn battled for one hundred and forty-three years, as soon as they fell down they had to stand up again and fight on. But in the end, the Christian lord Olaf Tryggvason, who has a great fate and luck, arrived with his christened men, and whoever slain by a Christian would stay dead. Thus the pagan curse was finally dissolved by the arrival of Christianity. After that, the noble man, king Olaf, went back to his realm.
The battle of Högni and Heðinn is recorded in several medieval sources, including the skaldic poem Ragnarsdrápa, Skáldskaparmál (section 49), and Gesta Danorum: king Högni's daughter, Hildr, is kidnapped by king Heðinn. When Högni comes to fight Heðinn on an island, Hildr comes to offer her father a necklace on behalf of Heðinn for peace; but the two kings still battle, and Hildr resurrects the fallen to make them fight until Ragnarök. None of these earlier sources mentions Freyja or king Olaf Tryggvason, the historical figure who christianized Norway and Iceland in the 10th Century.
C. 1000, a pagan priestess (Völva) was buried with considerable splendour in Hagebyhöga in Östergötland. In addition to being buried with her wand, she had received great riches which included horses, a wagon and an Arabian bronze pitcher. There was also a silver pendant which represents a woman with a broad necklace around her neck. This kind of necklace was only worn by the most prominent women during the Iron Age and some have interpreted it as Freyja's favourite necklace Brísingamen. The pendant may represent Freyja herself.