The magnetic tape includes a non-magnetic support; a magnetic layer including ferromagnetic powder and a binding agent on one surface side of the non-magnetic support; and a back coating layer including non-magnetic powder and a binding agent on the other surface side of the non-magnetic support, in which an isoelectric point of a surface zeta potential of the magnetic layer is equal to or smaller than 3.8, and an isoelectric point of a surface zeta potential of the back coating layer is equal to or smaller than 3.0, a magnetic tape cartridge, and a magnetic tape apparatus including this magnetic tape.

The invention provides high coercivity magnetic materials based on FeNi alloys having an L1.sub.0 phase structure, and methods for making the materials.

A rare earth permanent magnet includes a main phase composed of a main phase particle and a grain boundary present among a plurality of the main phase particles. The grain boundary includes a region whose electric resistance is higher than that of the main phase.

A sintered annular magnet with a radial orientation of a remanent magnetic field, including: a principal annular part made from a ferromagnetic material, that has a first degree of magnetic anisotropy in the radial direction; and an annular reinforcing part fixed to the principal part of the magnet, the reinforcing part being made from same ferromagnetic material as the ferromagnetic material forming the principal part, and that has a second degree of magnetic anisotropy in the radial direction, the first degree being higher than the second degree.

A permanent magnet of an embodiment includes: a composition represented by a composition formula: R(Fe.sub.pM.sub.qCu.sub.rCo.sub.1-p-q-r).sub.z, where R is at least one element selected from rare-earth elements, M is at least one element selected from Zr, Ti, and Hf, and relations of 0.3≦p≦0.4, 0.01≦q≦0.05, 0.01≦r≦0.1, and 7≦z≦8.5 (atomic ratio) are satisfied; and a structure including a cell phase having a Th.sub.2Zn.sub.17 crystal phase, and a cell wall phase existing to surround the cell phase. An average magnetization of the cell wall phase is 0.2 T or less.

A permanent magnet of an embodiment includes a sintered compact, the sintered compact including: a composition expressed by R.sub.pFe.sub.qM.sub.rCu.sub.sCo.sub.100-p-q-r-s, (R is at least one element selected from rare earth elements, M is at least one element selected from Zr, Ti, and Hf, 10.5≦p≦12.5 atomic %, 24≦q≦40 atomic %, 0.88≦r≦4.5 atomic %, and 3.5≦s≦10.7 atomic %); and a structure having crystal grains each composed of a main phase including a Th.sub.2Zn.sub.17 crystal phase, and a crystal grain boundary of the crystal grains. An average crystal grain diameter of the crystal grains is 50 μm or more and 100 μm or less, and a ratio of the crystal grains having a crystal grain diameter of 50 μm or more is 75% or more.

A step of, while a powder of an RLM alloy (where RL is Nd and/or Pr; M is one or more elements selected from among Cu, Fe, Ga, Co, Ni and Al) and a powder of an RH compound (where RH is Dy and/or Tb; and the RH compound is one, or two or more, selected from among an RH fluoride, an RH oxide, and an RH oxyfluoride) are present on the surface of a sintered R-T-B based magnet, performing a heat treatment at a sintering temperature of the sintered R-T-B based magnet or lower is included. The RLM alloy contains RL in an amount of 65 at % or more, and the melting point of the RLM alloy is equal to or less than the temperature of the heat treatment. The heat treatment is performed while the RLM alloy powder and the RH compound powder are present on the surface of the sintered R-T-B based magnet at a mass ratio of RLM alloy:RH compound=9.6:0.4 to 5:5.

A step of, while a powder of an RLM alloy (where RL is Nd and/or Pr; M is one or more elements selected from among Cu, Fe, Ga, Co, Ni and Al) which is produced through atomization and a powder of an RH compound (where RH is Dy and/or Tb) are present on the surface of a sintered R-T-B based magnet, performing a heat treatment at a sintering temperature of the sintered R-T-B based magnet or lower is included. The RLM alloy contains RL in an amount of 65 at % or more, and the melting point of the RLM alloy is equal to or less than the temperature of the heat treatment. The heat treatment is performed while the RLM alloy powder and the RH compound powder are present on the surface of the sintered R-T-B based magnet at a mass ratio of RLM alloy:RH compound=9.6:0.4 to 5:5.

A method for manufacturing an R-T-B based sintered magnet includes: 1) a step of preparing an R-T-B based sintered magnet material by sintering a molded body, the sintered magnet material having a particular composition and satisfying inequality expressions (1) and (2); 2) a high-temperature heat treatment step of heating the sintered magnet material to a heating temperature of 730° C. to 1,020° C. and then cooling the sintered magnet material to 300° C. at a cooling rate of 5° C./min or more; and 3) a low-temperature heat treatment step of heating the sintered magnet material after the high-temperature heat treatment step to 440° C. to 550° C.:

[T]−72.3[B]>0  (1)

([T]−72.3[B])/55.85<13[Ga]/69.72  (2)

where [T] is a T content in percent by mass, [B] is a B content in percent by mass, and [Ga] is a Ga content in percent by mass.

A method for manufacturing an R-T-B based sintered magnet includes: 1) a step of preparing an R-T-B based sintered magnet material by sintering a molded body, the sintered magnet material having a particular composition and satisfying inequality expressions (1) and (2); 2) a high-temperature heat treatment step of heating the sintered magnet material to a heating temperature of 730° C. to 1,020° C. and then cooling the sintered magnet material to 300° C. at a cooling rate of 5° C./min or more; and 3) a low-temperature heat treatment step of heating the sintered magnet material after the high-temperature heat treatment step to 440° C. to 550° C.:

[T]−72.3[B]>0  (1)

([T]−72.3[B])/55.85<13[Ga]/69.72  (2)

where [T] is a T content in percent by mass, [B] is a B content in percent by mass, and [Ga] is a Ga content in percent by mass.