<s>
A	O
spin	B-General_Concept
valve	I-General_Concept
is	O
a	O
device	O
,	O
consisting	O
of	O
two	O
or	O
more	O
conducting	O
magnetic	O
materials	O
,	O
whose	O
electrical	O
resistance	O
can	O
change	O
between	O
two	O
values	O
depending	O
on	O
the	O
relative	O
alignment	O
of	O
the	O
magnetization	O
in	O
the	O
layers	O
.	O
</s>
<s>
The	O
resistance	O
change	O
is	O
a	O
result	O
of	O
the	O
giant	B-General_Concept
magnetoresistive	I-General_Concept
effect	I-General_Concept
.	O
</s>
<s>
In	O
the	O
simplest	O
case	O
,	O
a	O
spin	B-General_Concept
valve	I-General_Concept
consists	O
of	O
a	O
non-magnetic	O
material	O
sandwiched	O
between	O
two	O
ferromagnets	O
,	O
one	O
of	O
which	O
is	O
fixed	O
(	O
pinned	O
)	O
by	O
an	O
antiferromagnet	O
which	O
acts	O
to	O
raise	O
its	O
magnetic	O
coercivity	O
and	O
behaves	O
as	O
a	O
"	O
hard	O
"	O
layer	O
,	O
while	O
the	O
other	O
is	O
free	O
(	O
unpinned	O
)	O
and	O
behaves	O
as	O
a	O
"	O
soft	O
"	O
layer	O
.	O
</s>
<s>
Spin	B-General_Concept
valves	I-General_Concept
work	O
because	O
of	O
a	O
quantum	O
property	O
of	O
electrons	O
(	O
and	O
other	O
particles	O
)	O
called	O
spin	O
.	O
</s>
<s>
This	O
results	O
from	O
a	O
large	O
negative	O
exchange	B-General_Concept
coupling	I-General_Concept
energy	I-General_Concept
between	O
ferromagnets	O
and	O
antiferromagnets	O
in	O
contact	O
.	O
</s>
<s>
The	O
basic	O
operating	O
principles	O
of	O
a	O
pseudo	O
spin	B-General_Concept
valve	I-General_Concept
are	O
identical	O
to	O
that	O
of	O
an	O
ordinary	O
spin	B-General_Concept
valve	I-General_Concept
,	O
but	O
instead	O
of	O
changing	O
the	O
magnetic	O
coercivity	O
of	O
the	O
different	O
ferromagnetic	O
layers	O
by	O
pinning	O
one	O
with	O
an	O
antiferromagnetic	O
layer	O
,	O
the	O
two	O
layers	O
are	O
made	O
of	O
different	O
ferromagnets	O
with	O
different	O
coercivities	O
e.g.	O
,	O
NiFe	O
and	O
Co	O
.	O
</s>
<s>
Spin	B-General_Concept
valves	I-General_Concept
are	O
used	O
in	O
magnetic	O
sensors	O
and	O
hard	B-Device
disk	I-Device
read	O
heads	O
.	O
</s>
<s>
They	O
are	O
also	O
used	O
in	O
magnetic	B-General_Concept
random	I-General_Concept
access	I-General_Concept
memories	I-General_Concept
(	O
MRAM	B-General_Concept
)	O
.	O
</s>
