Uniaxial anisotropy by "radiomagnetic" treatment; controlling factors in a new process

A new process-an electron-"radiomagnetic" treatment-for obtaining high-remanence, low-coercive-force loops in magnetic alloys was recently announced. As an example, 2-MeV electron irradiation of 6-mil-thick ring laminations of polycrystalline 5-80 Mo Permalloy with 10
¹⁷
e/cm
²
in an applied circumferential magnetic field of 0.2 Oe at
\sim100\deg
C produced record highs in remanence (∼6700 G) for this material. Additional studies of this process have been made to determine some of the controlling factors and the range of application. In particular, the effects of the dose (number of e/cm
²
) and of the preirradiation magnetic properties were examined. The results show that: 1) for a given dose of
1.1 \times 10^{17}
2-MeV e/cm
²
, the relative change in remanence (
\DeltaB_{r}/B_{r}
) is always positive, ranging from 10 to 50 percent, but varies inversely with the preirradiation value of remanence (B
r
); 2) for the same dose, the relative change in coercive force (
\DeltaH_{c}/H_{c}
) also depends upon the preirradiation value of remanence, but in a different way. For
B_{r} < 5000
G,
\DeltaH_{c}/H_{c}
is either negative or zero. For
B_{r} > 5000
G,
\DeltaH_{c}/H_{c}
is positive, ranging from 20 to 150 percent, and increases linearly with
B_{r}; 3
) if the dose is reduced to
\sim0.8 \times 10^{17}
e/cm
²
, then
\DeltaH_{c}/H_{c}
is reduced to a tolerable level (∼10 percent) with no significant sacrifice in the positive gain in remanence and rectangularity. Hence, there are optimum dose ranges in the "radio-magnetic" treatments of alloys, where significant gains in remanence may be obtained without appreciable increases in coercive force.