Patent ID: 8031425

Claim:
A method for writing magnetization states in a multi-layer continuous magnetic medium comprising N magnetic layers denoted as L( 1 ), L( 2 ), . . . , L(N), each magnetic layer comprising magnetic material continuously distributed in an X-Y plane defined by an X direction and a Y direction orthogonal to each other, consecutive magnetic layers separated by non-magnetic spacer material and distributed along a Z direction orthogonal to the X-Y plane, said N at least 3, said method comprising: selecting M layer groups denoted as G( 1 ), G( 2 ), . . . , G(M) from the N magnetic layers, said M layer groups consisting of P layer pairs and Q single layers, wherein 2≦M≦N-1, P≧1, and Q≧0; selecting magnetization states S( 1 ), S( 2 ), . . . , S(M) corresponding to the layer groups G( 1 ), G( 2 ), . . . , G(M), respectively, for each layer group G(m) (m=1, 2, . . . , or M) consisting of a layer pair, the magnetization state S(m) is denoted as [S 1 ; S 2 ](m), wherein S 1 and S 2 are a first and second magnetic state in a first and second magnetic layer, respectively, of the layer pair, wherein α 1 * and α 2 * are a first tilt angle and a second tilt angle at which a hard axis of the first magnetic layer and the second magnetic layer are respectively oriented with respect to the X direction, and wherein either or both of α 1 * and α 2 * are in a range of 0 to −90 degrees; for each layer group G(m′) (m′=1, 2, . . . , or M) consisting of a single layer, the magnetization state S(m′) is +1 or −1 if the magnetization is oriented at or opposite to, respectively, a tilt angle (α) at which an easy axis of the single layer is oriented with respect to the X direction; determining write currents I( 1 ), I( 2 ), . . . , I(M) sufficient to write the magnetization states S( 1 ), S( 2 ), . . . , S(M), respectively; for a set of indexes {i 1 , i 2 . . . , i m } such that each index maps to a unique integer in the set of integers{1, 2, . . . , M}, applying the write currents in a sequential order of I(i 1 ),I(i 2 ), . . . , I(i M ) to a magnetic write head moving in the X direction, resulting in generating the magnetization states S(i 1 ), S(i 2 ), . . . , S(i M ) for the layer groups of G(i 1 ), G(i 2 ), . . . , G(i M ), respectively, wherein the write current I(i m ) corresponding to layer group G(i m ) does not change the magnetization state of layer group G(i n ) (n<m) for m=2, 3, . . . , M), and wherein for each layer group G(m) consisting of said layer pair, said generating comprises said magnetic write head writing the magnetization state [S 1 ; S 2 ](m) by simultaneously writing the magnetic states S 1 and S 2 .