Magnetic recording medium, magnetic storage apparatus, and method for manufacturing magnetic recording medium
A magnetic recording medium includes a substrate, an underlayer, a first magnetic layer, and a second magnetic layer in this order. The first magnetic layer includes magnetic grains having a L1 0 structure, and the second magnetic layer has a granular structure including magnetic grains having a L1 0 structure, and a grain boundary portion including hexagonal boron nitride. A (111) plane of the magnetic grains included in the first magnetic layer is covered with boron nitride at an interface with the second magnetic layer. The magnetic grains included in the second magnetic layer are epitaxially grown from a (001) plane of the magnetic grains included in the first magnetic layer. The magnetic grains included in the first magnetic layer and the magnetic grains included in the second magnetic layer are columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively.
1 . A magnetic recording medium comprising:
a substrate, an underlayer, a first magnetic layer, and a second magnetic layer stacked in this order, wherein:
the first magnetic layer includes magnetic grains having a L1 0 structure,
the second magnetic layer has a granular structure including magnetic grains having a L1 0 structure, and a grain boundary portion including hexagonal boron nitride,
a (111) plane of the magnetic grains included in the first magnetic layer is covered with boron nitride at an interface with the second magnetic layer,
the magnetic grains included in the second magnetic layer are epitaxially grown from a (001) plane of the magnetic grains included in the first magnetic layer, and excluding the (111) plane of the magnetic grains included in the first magnetic layer,
the magnetic grains included in the first magnetic layer and the magnetic grains included in the second magnetic layer are columnar crystals penetrating the first magnetic layer and the second magnetic layer, respectively,
the boron nitride covering the (111) plane of the magnetic grains included in the first magnetic layer is hexagonal boron nitride having a (001) plane parallel to the (111) plane,
the hexagonal boron nitride included in the grain boundary portion of the second magnetic layer has a (001) plane surrounding a side surface of the magnetic grains included in the second magnetic layer, and
the hexagonal boron nitride included in the grain boundary portion of the second magnetic layer has a crystal orientation that gradually changes at an interface with the boron nitride at the interface between the first magnetic layer and the second magnetic layer.
2 . The magnetic recording medium as claimed in claim 1 , wherein the magnetic grains having the L1 0 structure and included in the first magnetic layer and the second magnetic layer are FePt alloy grains.
3 . A method for manufacturing the magnetic recording medium according to claim 1 , comprising:
forming a boron nitride layer by sputtering, between forming the first magnetic layer by sputtering and forming the second magnetic layer by sputtering.
4 . A magnetic storage apparatus comprising:
a magnetic recording medium according to claim 1 ; and
a head configured to record information on and reproduce information from the magnetic recording medium.
5 . The magnetic recording medium as claimed in claim 1 , wherein:
the magnetic grains included in the first magnetic layer has an aspect ratio in a range of 0.1 to 1.5, and
the aspect ratio is determined from t/D, where t denotes a height of the magnetic grains included in the first magnetic layer, and D denotes an equivalent diameter of the magnetic grains included in the first magnetic layer.
6 . The magnetic recording medium as claimed in claim 1 , wherein:
the magnetic grains included in the second magnetic layer has an aspect ratio in a range of 1.2 to 2.5, and
the aspect ratio is determined from t/D, where t denotes a height of the magnetic grains included in the second magnetic layer, and D denotes an equivalent diameter of the magnetic grains included in the second magnetic layer.
7 . The magnetic recording medium as claimed in claim 1 , wherein:
the magnetic grains included in the first magnetic layer has a first aspect ratio in a range of 0.1 to 1.5,
the first aspect ratio is determined from t 1 /D 1 , where t 1 denotes a height of the magnetic grains included in the first magnetic layer, and D 1 denotes an equivalent diameter of the magnetic grains included in the first magnetic layer,
the magnetic grains included in the second magnetic layer has a second aspect ratio in a range of 1.2 to 2.5, and
the second aspect ratio is determined from t 2 /D 2 , where t 2 denotes a height of the magnetic grains included in the second magnetic layer, and D 2 denotes an equivalent diameter of the magnetic grains included in the second magnetic layer.
8 . The magnetic recording medium as claimed in claim 1 , wherein a content of the hexagonal boron nitride in the second magnetic layer is in a range of 25 vol % to 50 vol %.
9 . The magnetic recording medium as claimed in claim 1 , wherein a content of the hexagonal boron nitride in the second magnetic layer is in a range of 35 vol % to 45 vol %.