Magnetic Microstructure and Properties of the Nanocrystalline Hard Magnet Terbium

Abstract

We present an experimental study of the magnetic properties and magnetic microstructure in the nanocrystalline hard magnet Tb. Field-dependent small-angle neutron scattering (SANS) data suggest that up to applied fields of several Tesla the magnetization remains 'locked in' to the basal planes of the hcp crystal lattice of each individual crystallite; as a consequence, domain-wall movement along the basal planes is eliminated as a mechanism for magnetization reversal, and the coercive field is substantially increased.Introduction The dependence of the magnetic properties of nanocrystalline hard magnets on the nanoscale microstructure is the subject of current research. Micromagnetics computer simulations (for instance, Ref.[1]) predict remanence and coercivity in qualitative agreement with experimental data, but their predictions have not been verified on a microscopic scale. This is a consequence of the inadequate lateral resolution of present microscopic techniques (Kerr, magnetic force and Lorentz microscopy) and of their inability to image the magnetic domain structure in the bulk (as opposed to at the surface). At present, the only known technique with a potential to resolve the magnetic microstructure in the bulk and on the length scale of nanometers is magnetic smallangle neutron scattering (SANS). SANS data have provided insight into the magnetic microstructure of soft magnetic nanocrystalline samples [2][3][4][5], yielding quantitative results for the magnetic microstructure, the exchange-stiffness constant, and the magnitude and microstructure of the magnetic anisotropy [5,6]. We have investigated nanocrystalline Tb as a model nanocrystalline hard magnet; the present paper complements a first report of the scattering data [7] with results of the magnetic characterization.

Structural and magnetic properties of bulk nanocrystalline Erbium metal

“…As a result, some nanostructured heavy rare earth metals, including Gd, Tb, and Dy, have been prepared and widely studied for their structure and magnetic properties. [1][2][3][4][5][6][7][8][9][10] As one of the heavy rare earth elements, Erbium (Er) had been intensively studied for its complex magnetic structures and magnetic properties. [11][12][13][14][15][16][17][18] Er metal has hexagonal close packed (hcp) crystal structure, and it undergoes three differentmagnetic phase transitions below 100 K. At T N of 85 K, a c-axis modulated sinusoidal structure appears; then with decreasing temperature at T B of 52 K a basal plane modulated structure, namely a quasi anti-phase domain magnetic structure; finally at T C of 20 K a conical ferromagnetic structure.…”

“…Similar coercive force enhancement in nanocrystalline Dy and Tb metals was also reported previously. [5][6][7] The magnetic structure of polycrystalline Er metal is quite complex. As the temperature is down to 85 K, the metal becomes from paramagnetic to anti-ferromagnetic with a c-axis modulated (CAM) structure, which turns to a basal plane modulated structure at 52 K with the squaring off of the c-axis component wave modulation; below 20 K, it changes to a conical ferromagnetic structure.…”

“…Similar phenomena have been observed and reported in previous studies for Dy and Tb nanocrystalline samples. 6,7,10 …”