Hydrostatic pressure and hexagonal magnetic anisotropy of hematite

Effective hexagonal magnetic anisotropy of hematite: Accounting for higher-order invariants

“…In [4], this discrepancy is explained by the residual after growth mechanical stresses in a sample. In [8], we sug gested a mechanism explaining the increase in the effective hexagonal magnetic anisotropy constant in the case when the crystal is not perfect. The residual mechanical stresses arising in the process of fast cool ing after the synthesis [9] were simulated by a hypo thetic hydrostatic pressure.…”

“…The hydrostatic pressure P contributes to the effective uniaxial anisotropy constant in the form a -μP (a is the uniaxial crystalline anisotropy constant and μ is a constant, see below). In turn, this constant determines the contribution Δe to the effective hexagonal anisot ropy of the crystal [8]: Δe = d 2 /4(a -μP) (d is the fourth order magnetic anisotropy constant). The model constructed in [8] led to rather a high hydro static pressure (~10 10 dyn/cm 2 ).…”

“…In turn, this constant determines the contribution Δe to the effective hexagonal anisot ropy of the crystal [8]: Δe = d 2 /4(a -μP) (d is the fourth order magnetic anisotropy constant). The model constructed in [8] led to rather a high hydro static pressure (~10 10 dyn/cm 2 ). Our estimates pre sented in [8] show that, despite a significant value, such pressure is feasible, because it agrees with calcu lated thermal strains of the crystal due to the tempera ture drop ΔT ~ 10 2 -10 3°C as a result of fast cooling until termination of the crystallization process.…”

“…The model constructed in [8] led to rather a high hydro static pressure (~10 10 dyn/cm 2 ). Our estimates pre sented in [8] show that, despite a significant value, such pressure is feasible, because it agrees with calcu lated thermal strains of the crystal due to the tempera ture drop ΔT ~ 10 2 -10 3°C as a result of fast cooling until termination of the crystallization process.…”

“…As was noted above, this term simulates the residual mechani cal stresses in a sample [8]. Another possible reason for the stresses is the contact of the crystal with piezoelec tric converters attached to its basal faces.…”