Stress-Induced Magnetic Properties of Gadolinium Iron Garnet Nanoscale-Thin Films: Implications for Spintronic Devices

Abstract

The insulating nature and the low intrinsic damping of rare earth iron garnets made them the material of choice for spintronic research. While yttrium iron garnet (YIG) thin films are well studied and especially known for their ultralow Gilbert damping parameter, recently other rare earth iron garnet (RIG) thin films with more complex magnetic structures have gained interest. Tunable magnetic properties like the magnetic compensation temperature or perpendicular magnetic anisotropy (PMA) are hereby of great interest for the implementation in spintronic devices. In this regard, calculations predict PMA which can be induced by magnetoelastic anisotropy for the RIGs, depending on the substrate choice and subsequent film strain. We have therefore investigated the influence of lattice mismatch provided by various garnet substrates and film stoichiometry on the structural and magnetic properties of gadolinium iron garnet (GdIG) thin films with thicknesses between 13 and 218 nm. Epitaxial, single-crystalline films exhibiting smooth interfaces were prepared by pulsed laser deposition at elevated temperatures. PMA is obtained for GdIG thin films grown under tensile in-plane strain on Gd3Sc2Ga3O12 (GSGG) substrates. Furthermore, a thickness series reveals a slow structural relaxation and PMA even for 218 nm thick GdIG films. In contrast, slightly off-stoichiometric films show a reduction or even loss in PMA. All GdIG films exhibit a magnetic compensation point in the range between 210–260 K, which is lower than for bulk (286 K). In addition, a temperature dependent spin reorientation transition was observed for GdIG/GSGG samples. Therefore, GdIG films provide tunable magnetic properties controllable by film strain, stoichiometry, and temperature, which will be beneficial for further research in the related fields of magnonics and spintronics.

Temperature Evolution of Magnon Propagation Length in Tm3Fe5O12 Thin Films: Roles of Magnetic Anisotropy and Gilbert Damping

“…An annular detector with a small collector angle (24−48 mrad) was used to highlight strain (Bragg) contrast over mass (Z) contrast. 49 The TmIG film shows columnar features attributed to strain contrast. An atomically resolved STEM image at the TmIG film-Pt interface (Figure 2b) reveals a single-crystalline TmIG film under the polycrystalline Pt layer, with the bright spots indicating columns of Tm and Fe.…”

“…Films with 46 nm ≤ t ≤ 236 nm possess IP easy axes while the 28 nm film has an OOP easy axis of magnetization, which was confirmed via IP-magnetometry and OOP p -MOKE measurements (see Supplementary Figure 3e). The total magnetic anisotropy of a (111)-oriented TmIG film, neglecting growth and interfacial anisotropies, has contributions from shape anisotropy ( K shape ), cubic magnetocrystalline anisotropy ( K mc ), and magnetoelastic anisotropy ( K me ) ,, i.e. K e f f = K s h a p e + K m c + K m e = − 1 2 μ 0 M S 2 − K 1 12 − 9 4 λ 111 c 44 true( π 2 − β true) where K 1 is the magnetocrystalline anisotropy coefficient, λ 111 is the magnetostriction along the [111] direction, c 44 is the shear modulus, and β is the corner angle of the rhombohedrally distorted unit cell. For a negative magnetostriction (λ 111 = −5.2 × 10 –6 for bulk TmIG), the tensile IP strain, which results from the difference in lattice parameters ( a GSGG = 12.57 Å and a TmIG = 12.32 Å) promotes PMA ( K eff > 0). ,, PMA is expected for fully strained films (28 nm), but strain relaxation in thicker films reduces the magnetoelastic contribution, and the easy axis reorients to the IP direction …”

“…Films with 46 nm ≤ t ≤ 236 nm possess IP easy axes while the 28 nm film has an OOP easy axis of magnetization, which was confirmed via IP-magnetometry and OOP p-MOKE measurements (see Supplementary Figure 3e). The total magnetic anisotropy of a (111)-oriented TmIG film, neglecting growth and interfacial anisotropies, has contributions from shape anisotropy (K shape ), cubic magnetocrystalline anisotropy (K mc ), and magnetoelastic anisotropy (K me ) 47,49,60 i.e.…”

Rare Earth Based Iron Garnet – A Survey on Its Magnetic Properties

“…In this mechanism at high temperatures, Gd and Fe ions that are present on the surface layer, their spins are largely decoupled and the spins of Fe ions at the surface align themselves along the magnetic moments of the core. The magnetic anisotropy which is largely influenced by the presence of a magnetic compensation point can be fine-tuned in GdIG samples by preparing it on a different substrate and thereby varying the film strain [47]. The magnetic behaviour is also influenced by inter-particle interactions.…”

Sputtered terbium iron garnet films with perpendicular magnetic anisotropy for spintronic applications

“…16,17 Lately, however, the focus has started to shift towards REIGs with magnetic rare-earth elements such as Tm 3 Fe 5 O 12 (TmIG), Eu 3 Fe 5 O 12 (EuIG), Tb 3 Fe 5 O 12 (TbIG), etc. [18][19][20][21][22][23] In these films, it is possible to obtain straininduced PMA due to the lattice mismatch with Gd 3 Ga 5 O 12 (GGG) or similar substrates. [24][25][26] Moreover, coupled lattice dynamics, together with magnetic and angular compensation in ferrimagnets, allow high-speed and efficient magnetization manipulation by means of magnetic fields 27 and spinorbit torques.…”