Magnetoresistive effect oscillator
A magnetoresistive effect oscillator executes a first step of applying a current, which has a first current density larger than a critical current density J O for oscillation, to a magnetoresistive effect element for a time T P , and then executes a second step of applying a current, which has a second current density J S smaller than the first current density and not smaller than the critical current density J O for oscillation, to the magnetoresistive effect element. The following formulae (1), (2) and (3), or the following formulae (1) and (4) are satisfied on an assumption that an average value of the first current density during the time T P in the first step is J P , a critical current density for magnetization reversal of the magnetoresistive effect element is J R , and a magnetization reversal time of the magnetoresistive effect element is T R : 0.1 × T R ( J R - J O ) J p - J S < T p < 0.9 × T R J R - J O J S - J O ( 1 ) T P < T R ( J R - J O ) J P - J O ( 2 ) J R ≤ J P ( 3 ) J P < J R . ( 4 )
1. A magnetoresistive effect oscillator comprising:
a magnetoresistive effect element including a first magnetic layer, a second magnetic layer, and a spacer layer sandwiched between the first magnetic layer and the second magnetic layer; and
a current applying unit that applies a current to the magnetoresistive effect element,
wherein the current applying unit executes a first step of applying a current, which has a first current density larger than a critical current density J O for oscillation of the magnetoresistive effect element, to the magnetoresistive effect element for a time T P ,
the current applying unit executes, after the first step, a second step of applying a current, which has a second current density J S smaller than the first current density and not smaller than the critical current density J O for oscillation, to the magnetoresistive effect element such that the magnetoresistive effect element oscillates at a predetermined frequency, and
the following formulae (1), (2) and (3), or the following formulae (1) and (4) are satisfied on an assumption that an average value of the first current density during the time T P in the first step is J P , a critical current density for magnetization reversal of the magnetoresistive effect element is J R , and a magnetization reversal time of the magnetoresistive effect element is T R :
0.1
×
T
R
(
J
R
-
J
O
)
J
p
-
J
S
<
T
p
<
0.9
×
T
R
J
R
-
J
O
J
S
-
J
O
(
1
)
T
p
<
T
R
(
J
R
-
J
O
)
J
P
-
J
O
(
2
)
J
R
≤
J
P
(
3
)
J
P
<
J
R
.
(
4
)
2. The magnetoresistive effect oscillator according to claim 1 , wherein the following formula (5) is satisfied:
0.25
×
T
R
(
J
R
-
J
O
)
J
p
-
J
S
<
T
p
<
0.75
×
T
R
J
R
-
J
O
J
S
-
J
O
.
(
5
)
3. The magnetoresistive effect oscillator according to claim 2 , wherein the following formula (6) is satisfied:
0.5
×
T
R
(
J
R
-
J
O
)
J
p
-
J
S
<
T
p
<
0.5
×
T
R
J
R
-
J
O
J
S
-
J
O
.
(
6
)
4. The magnetoresistive effect oscillator according to claim 3 , wherein the following formula (7) is satisfied:
0.75
×
T
R
(
J
R
-
J
O
)
J
p
-
J
S
<
T
p
<
0.25
×
T
R
J
R
-
J
O
J
S
-
J
O
.
(
7
)
5. The magnetoresistive effect oscillator according to claim 1 , wherein the following formula (8) is satisfied:
0.96
×
T
R
(
J
R
-
J
O
)
(
J
P
-
0.96
J
S
)
≤
T
p
≤
0.98
×
T
R
(
J
R
-
J
O
)
(
J
P
-
0.98
J
s
)
.
(
8
)