مرکز منطقه ای اطلاع رساني علوم و فناوري - Easy plane antiferromagnets (AFEP) for applications: Hematite

Abstract :

There are two modes of collective oscillations of spins in AFEP\´s: a gyrotropical (in relation to magnetic moment) mode with frequencies ω1Kand an ungyrotropical one with ω2K. Their strong nonlinear connection gives rise to some effects of technical interest both for cm and mm ranges of microwaves: mixing of oscillations, parallel pumping, biresonance frequency doubling, etc. The influence of magnetoelasic (m.e.) interaction on ω1Kis amplified by exchange field HE: $\\omega _{10}/\\gamma )^{2} = H(H + H_{D}) + 2H_{E}H_{mes}(P)$ where, for hematite (α-Fe2O3), HE= 9.2×10⁶Oe and, from our measurements, Hmes(P)= (0.74 - 6.0p) Oe at T = 300 K, $p\\parallel \\overrightarrow{H}\\perp C_{3}$ , and $0.1 \\leq p \\leq 1.5 k$ bar. Because of this, a performance of simple microwave power piezomodulator for mm range is possible even with a single crystal which is not of high quality ( $\\Delta \\omega _{10}/\\gamma \\sim450$ Oe). The "shear" m.e. interaction leads to a strong dependence of the sound velocity in hematite on magnetic field: $V_{s} = V_{scs} [1 - 2H_{E}H_{s}/(\\omega_{10}/\\gamma )^{2}]^{1/2}$ . The field variations of eigenfrequencies of hematite single crystal balls quasielastic oscillations, detected with the help of AFMR, give Hsup to 0.7 Oe.