Recording layer and multilayered soft underlayer
View Patent ↗A media for perpendicular recording and a method of creating the media is provided. The media includes a hard recording layer and a soft underlayer (SUL). The SUL is composed of at least two anti-ferromagnetically coupled (AFC) sub-underlayers. The sub-underlayers respond to a magnetic field established during dynamic reversal with respective magnetic fields. The sub-underlayers are formed and disposed to differ in one or more magnetic moment, anisotropy, and thickness, so that their respective magnetic fields constructively interfere in one or more points in the hard recording layer, thereby reducing a total SUL magnetic field response to the dynamic reversal field approximately to zero at one or more points in the hard recording layer, which reduces side track erasure.
1. A device comprising:
a substrate;
a hard magnetic layer; and
a Soft UnderLayer (SUL) formed between the substrate and the hard magnetic layer and comprising:
a first sub-underlayer; and
a second sub-underlayer, wherein
the first sub-underlayer and the second sub-underlayer are adjacent and anti-ferromagnetically coupled (AFC),
one of the sub-underlayers deposited to differ in one or more of thickness, magnetic moment, and anisotropy from the other sub-underlayer,
respective magnetic field responses of each sub-underlayer to a magnetic field established during dynamic reversal interfere to create a total SUL magnetic field response to the dynamic reversal magnetic field that is approximately zero at one or more points in the hard magnetic layer, and
the second sub-underlayer has a greater magnetic moment and is further away from the hard magnetic layer than the first sub-underlayer.
2. The media of claim 1 , wherein the first sub-underlayer is thinner than the second sub-underlayer.
3. The media of claim 1 , wherein the minimum thickness of the SUL is determined by
h
min
S
U
L
=
γ
(
u
+
1
)
W
tip
B
s
tip
(
u
-
1
)
2
B
s
S
U
L
,
wherein, h is the minimum thickness of the SUL, W tip is the width of the writer pole, γ is the ratio associated with the write pole saturation level and flux leakage, u is the permeability of the SUL, B tip is the moment of the tip, and B SUL is the moment of the SUL.
4. The media of claim 1 , wherein either Ms 1 t 1 <Ms 2 t 2 or Ms 1 t 1 >Ms 2 t 2 holds, wherein Ms 1 and t 1 respectively are the moment and thickness of the sub-underlayer closer to the hard magnetic layer and Ms 2 and t 2 respectively are the moment and thickness of the sub-underlayer farther from the hard magnetic layer, and the total SUL field strength decays more rapidly than a total field strength produced by a dual layer SUL with Ms 1 t 1 =Ms 2 t 2 under the same dynamic reversal field.
5. The media of claim 1 , further comprising a third sub-underlayer.
6. The media of claim 5 , wherein the three sub-underlayers are chosen such that one of the conditions Ms 1 t 1 +Ms 3 t 3 =Ms 2 t 2 , Ms 1 t 1 +Ms 3 t 3 >Ms 2 t 2 Ms 1 t 1 +Ms 3 t 3 <Ms 2 t 2 holds, wherein Ms is the moment of respective underlayers and t is the thickness of respective underlayers.
7. A method comprising:
depositing a soft underlayer (SUL) on a substrate; and
depositing a hard recording layer on the SUL, wherein
said depositing the SUL includes depositing:
a first sub-underlayer; and
a second sub-underlayer such that the second sub-underlayer is further away from the hard recording layer than the first sub-underlayer, wherein
the first sub-underlayer and the second sub-underlayer are anti-ferromagnetically coupled (AFC) sub-underlayers,
the first sub-underlayer and the second sub-underlayer are in a relative configuration selected so that each SUL sub-underlayer produces a respective magnetic field responsive to a dynamic reversal magnetic field, each respective magnetic field of a magnitude and polarity to cause destructive interference between the sub-underlayer fields at one or more points in the hard recording layer, reducing a total field perceived by the hard recording layer emanating from the SUL at those points to approximately zero at one or more points in the hard recording layer, and
the second sub-underlayer has a greater magnetic moment than the first sub-underlayer.
8. The method of claim 7 , further comprising determining the total thickness of the SUL based on:
h
min
S
U
L
=
γ
(
u
+
1
)
W
tip
B
s
tip
(
u
-
1
)
2
B
s
S
U
L
,
wherein, h is the minimum thickness of the SUL, W tip is the width of the writer pole, γ is the ration associated with the write pole saturation level and flux leakage, u is the permeability of the SUL, B tip is the moment of the tip, and B SUL is the moment of the SUL, and the at least two sub-underlayers are of at least two different materials and moments and thicknesses.
9. A media comprising:
a substrate;
a hard recording layer; and
a Soft UnderLayer (SUL) formed between the substrate and the hard recording layer and comprising at least two anti-ferromagnetically coupled (AFC) sub-underlayers, at least one of the sub-underlayers deposited to differ in one or more of thickness, magnetic moment, and anisotropy from the other sub-underlayers, wherein a vector sum of magnetic fields emanating from each sub-underlayer, at a location inside the hard recording layer during dynamic reversal, is substantially zero, and wherein further one of the sub-underlayers has a greater magnetic moment and is further away from the hard recording layer than the other sub-underlayer.
10. The media of claim 9 , wherein the other sub-underlayer is thinner than the sub-underlayer having a greater magnetic moment.
11. The media of claim 9 , wherein the minimum thickness of the SUL is determined by
h
min
S
U
L
=
γ
(
u
+
1
)
W
tip
B
s
tip
(
u
-
1
)
2
B
s
S
U
L
,
wherein, h is the minimum thickness of the SUL, W tip is the width of the writer pole, γ is the ratio associated with the write pole saturation level and flux leakage, u is the permeability of the SUL, B tip is the moment of the tip, and B SUL is the moment of the SUL.
12. The media of claim 9 , wherein either Ms 1 t 1 <Ms 2 t 2 or Ms 1 t 1 >Ms 2 t 2 holds, wherein Ms 1 and t 1 respectively are the moment and thickness of the sub-underlayer closer to the hard recording layer and Ms 2 and t 2 respectively are the moment and thickness of the sub-underlayer farther from the hard recording layer, and the total SUL field strength decays more rapidly than a total field strength produced by a dual layer SUL with Ms 1 t 1 =Ms 2 t 2 under the same dynamic reversal field.
13. The media of claim 9 , wherein there are three sub-underlayers.
14. The media of claim 13 , wherein the three sub-underlayers are chosen such that one of the conditions Ms 1 t 1 +Ms 3 t 3 =Ms 2 t 2 , Ms 1 t 1 +Ms 3 t 3 >Ms 2 t 2 Ms 1 t 1 +Ms 3 t 3 <Ms 2 t 2 holds, wherein Ms is the moment of respective underlayers and t is the thickness of respective underlayers.
15. The media of claim 9 , wherein the SUL includes two sub-underlayers, and the sub-underlayer farther from the hard recording layer exhibits a higher normalized field strength, measured at a point in the hard recording layer where the total SUL field is approximately zero, than a corresponding layer of a different SUL meeting the condition that Ms 1 t 1 =Ms 2 t 2 , wherein Ms 1 and t 1 respectively are the moment and thickness of the sub-underlayer closer to the hard recording layer and Ms 2 and t 2 respectively are the moment and thickness of the sub-underlayer farther from the hard recording layer, in response to the same dynamic reversal field strength.