Ferromagnetic tunnel junction element and method of driving ferromagnetic tunnel junction element

Abstract

In a tunnel junction element having a ferromagnetic free layer, an insulating layer and a ferromagnetic fixed layer, in order to reduce the current necessary for spin-transfer magnetization reversal operation in the tunnel junction element, the ferromagnetic free layer comprises first and second ferromagnetic layers, a nonmagnetic metal layer is provided between these ferromagnetic layers, the nonmagnetic metal layer is such that magnetic coupling is preserved between the first and second ferromagnetic layers, also such that there is no influence on the crystal growth of the first and second ferromagnetic layers, the first ferromagnetic layer and the second ferromagnetic layer are placed such that the first ferromagnetic layer is in contact with the insulating layer, and the second ferromagnetic layer has a smaller magnetization than the first ferromagnetic layer.

1 . A ferromagnetic tunnel junction element, comprising a ferromagnetic free layer, an insulating layer, and a ferromagnetic fixed layer which together with the ferromagnetic free layer sandwiches the insulating layer, wherein
 the ferromagnetic free layer comprises a first ferromagnetic layer in contact with the insulating layer, a nonmagnetic metal layer, and a second ferromagnetic layer which together with the first ferromagnetic later sandwiches the nonmagnetic metal layer and which has a saturation magnetization smaller than the saturation magnetization of the first ferromagnetic layer,   the film thickness of the nonmagnetic metal layer is set to a film thickness at which the magnetic coupling between the first ferromagnetic layer and the second ferromagnetic layer is ferromagnetic coupling, and   the magnetization direction of the first ferromagnetic layer is determined according to the magnetization direction of the second ferromagnetic layer.   
     
     
         2 . The ferromagnetic tunnel junction element according to  claim 1 , wherein the first ferromagnetic layer comprises any one among a single metal selected from the magnetic metal group consisting of iron, cobalt, and nickel, or an alloy comprising one metal selected from the magnetic metal group, or a compound comprising one metal selected from the magnetic metal group and metalloid element, and wherein the insulating layer comprises a single crystal or fine crystals or magnesium oxide. 
     
     
         3 . The ferromagnetic tunnel junction element according to  claim 1 , wherein the insulating layer and the first ferromagnetic layer are epitaxially joined with each other, and the material of the nonmagnetic metal layer is selected from materials which prevent mutual influence of the crystallinity of the first and second ferromagnetic layers. 
     
     
         4 . The ferromagnetic tunnel junction element according to  claim 1  wherein the second ferromagnetic layer is of Permalloy. 
     
     
         5 . Magnetic random access memory, comprising as a storage element the ferromagnetic tunnel junction element according to  claim 1 . 
     
     
         6 . Magnetic random access memory, comprising as a storage element the ferromagnetic tunnel junction element according to  claim 4 .