O. Isnard

We investigate the complex magnetic behavior of LaFe12B6 by means of magnetostriction, and thermal expansion measurements in applied fields of up to 14 T, elucidating the interplay between crystal lattice and spins. As main results, we have discovered a remarkably large negative thermal expansion (NTE) and giant magnetostriction in this itinerant-electron system. Of particular interest are the low-temperature magnetostriction isotherms (T ≤ 5 K) all of which reach saturation discontinuously, by way of ultrasharp multistep transitions. These are rather unusual kind of first-order phase transitions. By contrast, the field-dependent magnetostriction varies smoothly at temperatures exceeding 5 K. A huge positive magnetostrictive effect of ΔV/V (20 K, 14 T) = 0.87% accompanies the field-induced first-order metamagnetic transition. In the vicinity of the Curie point, a magnetically driven giant NTE phenomenon with an average linear thermal expansion coefficient αL = −27 × 10−6 K−1 is observed.