مرکز منطقه ای اطلاع رساني علوم و فناوري - Static and anhysteretic magnetic properties of tapes

Abstract :

The anhysteretic remanence $\\bar{M}_{ar}(H_{o},T)$ of solidified suspensions of magnetic particles with predominant shape anisotropy is calculated from first principles for small dc fields Hoand arbitrary temperature $T < T_{B}$ (blocking temperature), describing the particle interactions by a mean field and assuming constant decrement of the ac field, $2H_{d}$ per cycle. For $H_{d}< 2H_{o}$ , the anhysteretic distribution of particle magnetizations is found to be subject to the condition that the net internal dc field $\\bar{H}_{i}$ is a minimum, and, for small Ho, to the condition, $\\bar{H}_{i} = 0$ . The theory yields $\\bar{M}_{ar}(H_{o},T)$ as a unique function of independently measurable static magnetic material properties, i.e., it contains no adjustable parameters and is hence quantitatively related to experimental data. Further, according to theory, if $\\bar{M}_{ar}(H_{o},T,T_{m})$ denotes $\\bar{M}_{ar}$ as acquired in Hoat T and measured at $T_{m}, \\bar{M}_{ar}(H_{o},T,T_{m} = T)$ is independent of $T$ for $H_{d} \\ll 2H_{o}$ , and $\\bar{M}_{ar}(H_{o},T,T_{m} \\neq T) = [M_{s}(T_{m})/M_{s}(T)] \\cdot \\bar{M}_{ar}(H_{o},T,T_{m} = T)$ . The thermoremanent magnetization acquired in Hoand measured at a temperature $T_{m} \\ll T_{B}$ , $\\bar{M}_{thr}(H_{o},T_{m})$ , is related to $\\bar{M}_{ar}(H_{o},T = T_{m}, T_{m})$ by $\\bar{M}_{thr}(H_{o},T_{m}) = [M_{s}(T_{m})/M_{s}(T_{B})]\\bar{M}_{ar}(H_{o},T=T_{m},T_{m})$ , where TBis the blocking temperature below which $\\bar{M}_{thr}$ becomes thermally stable. Up to a constant factor of about 2, the theoretical results agree quantitatively with the experimental data on all materials that correspond to the premises of the theory, i.e., solidified suspensions, tapes in particular, of particles having predominant shape anisotropy.