Magnetic recording medium, magnetic recording and reproducing apparatus, magnetic tape cartridge, and magnetic tape cartridge group

A magnetic recording medium comprising:

• a non-magnetic support;
• a magnetic layer including ferromagnetic powder;
• a non-magnetic layer including non-magnetic powder between the non-magnetic support and the magnetic layer;
• and
• a back coating layer including non-magnetic powder on a surface side of the non-magnetic support opposite to a surface side provided with the magnetic layer,
• wherein an average particle size of the ferromagnetic powder is 30 nm or less,
• a number distribution A of a plurality of bright regions, based on equivalent circle diameters thereof, in a binarized image of a secondary electron image obtained by imaging a surface of the magnetic layer by a scanning electron microscope at an acceleration voltage of 5 kV satisfies the following (1) to (3):
• (1) bright regions having an equivalent circle diameter of 1 nm or more and 50 nm or less are 10,000 or more and 30,000 or less;
• (2) bright regions having an equivalent circle diameter of 51 nm or more and 100 nm or less are 7,000 or more and 25,000 or less;
• and
• (3) bright regions having an equivalent circle diameter of 101 nm or more are 3,000 or more and 7,000 or less, and
• a number distribution B of a plurality of dark regions, based on equivalent circle diameters thereof, in a binarized image of a secondary electron image obtained by imaging a surface of the magnetic layer by a scanning electron microscope at an acceleration voltage of 2 kV satisfies the following (4) to (6):
• (4) dark regions having an equivalent circle diameter of 1 nm or more and 50 nm or less are 1,000 or more and 25,000 or less;
• (5) dark regions having an equivalent circle diameter of 51 nm or more and 100 nm or less are 200 or more and 5,000 or less;
• and
• (6) dark regions having an equivalent circle diameter of 101 nm or more are 200 or more and 350 or less.