Patent ID: 7924609

Claim:
A spin valve element driving method for obtaining an electromagnetic signal from a spin valve element, the spin valve element including an intermediate layer, which is an insulating layer or an electrically conductive nonmagnetic layer, and a pair of ferromagnetic layers including a fixed layer and a free layer sandwiching the intermediate layer, the fixed layer having a higher coercivity than the free layer, and being magnetized in a direction substantially perpendicular to a film plane thereof, the method comprising a driving step of passing current from one of the pair of ferromagnetic layers to the other through the intermediate layer, wherein in the driving step, an amount X of the current and the value Y of a magnitude of an external magnetic field satisfy both a first condition: ( A+BYD ) 2 −4 AD ( BY−CX )>0 and a second condition: −1<(( A+BYD )−(( A+BYD ) 2 −4 AD ( BY−CX )) 0.5 )/(2 AD )<(( A+BYD )+(( A+BYD ) 2 −4 AD ( BY−CX )) 0.5 )/(2 AD )<1 when A>0; and (( A+BYD )−(( A+BYD ) 2 −4 AD ( BY−CX )) 0.5 )/(2 AD )<1 when A<0, where X is positive when the current passes from the free layer toward the fixed layer, A=αγHu and B=αγ, α being the Gilbert damping constant, γ being the gyromagnetic ratio, and Hu being the component of the magnetic field, which is the sum of a magnetocrystalline anisotropy field crystal anisotropy magnetic field and a demagnetizing field of the free layer, perpendicular to the free layer, and C=μP/(Ms×V×e) and D=P 2 if the intermediate layer is an insulating layer, and C=(μP/(Ms×V×e))/(−16+3(P 1/2 +P −1/2 ) 3 ) and D=(P 1/2 +P −1/2 ) 3 /(−16+3(P 1/2 +P −1/2 ) 3 ) if the intermediate layer is an electrically conductive nonmagnetic layer, P being a spin polarization, μ being a Bohr magneton, Ms being a saturation magnetization of the free layer, V being a volume of the free layer, and e being an electronic charge.