3 research outputs found
Cobalt-Based Single-Ion Magnets on an Apatite Lattice: Toward Patterned Arrays for Magnetic Memories
Single-ion magnets (SIMs) that can
maintain magnetization direction on an individual transition metal
atom represent the smallest atomic-scale units for future magnetic
data storage devices and molecular electronics. Here we present a
robust extended inorganic solid hosting efficient SIM centers, as
an alternative to molecular SIM crystals. We show that unique dioxocobaltateÂ(II)
ions, confined in the channels of strontium hydroxyapatite, exhibit
classical SIM features with a large energy barrier for magnetization
reversal (<i>U</i><sub>eff</sub>) of 51–59 cm<sup>–1</sup>. The samples have been tuned such that a magnetization
hysteresis opens below 8 K and <i>U</i><sub>eff</sub> increases
by a factor of 4 and can be further enhanced to the highest values
among 3d metal complexes of 275 cm<sup>–1</sup> when Ba is
substituted for Sr. The SIM properties are preserved without any tendency
toward spin ordering up to a high Co concentration. At a maximal Co
content, a hypothetical regular hexagonal grid of SIMs with a 1 nm
interspacing on the (001) crystal facet would allow a maximal magnetic
recording density of 10<sup>5</sup> Gb/cm<sup>2</sup>
Cobalt-Based Single-Ion Magnets on an Apatite Lattice: Toward Patterned Arrays for Magnetic Memories
Single-ion magnets (SIMs) that can
maintain magnetization direction on an individual transition metal
atom represent the smallest atomic-scale units for future magnetic
data storage devices and molecular electronics. Here we present a
robust extended inorganic solid hosting efficient SIM centers, as
an alternative to molecular SIM crystals. We show that unique dioxocobaltateÂ(II)
ions, confined in the channels of strontium hydroxyapatite, exhibit
classical SIM features with a large energy barrier for magnetization
reversal (<i>U</i><sub>eff</sub>) of 51–59 cm<sup>–1</sup>. The samples have been tuned such that a magnetization
hysteresis opens below 8 K and <i>U</i><sub>eff</sub> increases
by a factor of 4 and can be further enhanced to the highest values
among 3d metal complexes of 275 cm<sup>–1</sup> when Ba is
substituted for Sr. The SIM properties are preserved without any tendency
toward spin ordering up to a high Co concentration. At a maximal Co
content, a hypothetical regular hexagonal grid of SIMs with a 1 nm
interspacing on the (001) crystal facet would allow a maximal magnetic
recording density of 10<sup>5</sup> Gb/cm<sup>2</sup>
Slow Spin Relaxation in Dioxocobaltate(II) Anions Embedded in the Lattice of Calcium Hydroxyapatite
Pure-phase cobalt-doped calcium hydroxyapatite
ceramic samples with composition Ca<sub>10</sub>(PO<sub>4</sub>)<sub>6</sub>[(CoO<sub>2</sub>)<sub><i>x</i></sub>(OH)<sub>1–2<i>x</i></sub>]<sub>2</sub>, where <i>x</i> = 0–0.2,
were synthesized by high-temperature solid-state reaction, and their
crystal structures, vibrational spectra, and magnetic properties were
studied. Co atoms are found to enter into the apatite trigonal channel
formally substituting H atoms and forming bent dioxocobaltateÂ(II)
anions. The anion exhibits single-molecule-magnet (SMM) behavior:
slow relaxation of magnetization below 8 K under a nonzero magnetic
field with an energy barrier of 63 cm<sup>–1</sup>. The barrier
value does not depend on the concentration of Co ions, virtually coincides
with the zero-field-splitting energy as determined from direct-current
magnetization, and is very close to the value obtained earlier for
cobalt-doped strontium hydroxyapatite. Moreover, the vibration frequencies
of the dioxocobaltateÂ(II) anion are found to be the same in calcium
and strontium apatite matrixes. The very weak dependence of the SMM
parameters on the matrix nature in combination with good chemical
and thermal stabilities of the compounds provides wide opportunities
to exploit the intrinsic properties of such a SMM-like anion