Ferromagnetism In Zn1 Research Articles

Enhancement of ferromagnetism in Zn 0.98 Co 0.02 O by quenching from high temperatures

Co-doped ZnO samples with above-room-temperature Curie point were fabricated by the standard solid-state reaction method. Ferromagnetic behavior varied with different quenching temperatures ranging from 1173 K to 573 K after calcination. Extensive analyses on structural and composition revealed that cobalt is homogeneously incorporated into the ZnO lattice forming solid solution instead of precipitation when x ≤ 0.02 in Zn1–xCoxO. In the case of Zn0.98Co0.02O, ferromagnetism was enhanced by decreasing the quenching temperature until 573 K. The coercive field measured by a vibrating sample magnetometer (VSM) at room temperature is around 60–80 Oe. The implication of the effect of quenching temperature in bulk Zn0.98Co0.02O is also discussed. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fe-doping effects of ferromagnetic Zn0.98−xFe0.02MgxO semiconductor

The X-ray diffraction patterns of the Zn0.98–xFe0.02MgxO (x=0, 0.05, 0.1, 0.2) powders showed no detectable MgO peaks for x⩽0.1, whereas clear MgO peaks x=0.2. All the peaks for the X-ray diffraction patterns of x⩽0.1 samples belong to the hexagonal (P63mc) lattice of ZnO. The hysteresis curve at 77K for the Zn0.88Mg0.1Fe0.02O indicated the coexistence of both a paramagnetic and a ferromagnetic phases. The temperature dependence of magneto-resistance curve shows semiconductor behavior over 220K.

Ferromagnetism in II–VI diluted magnetic semiconductor Zn1−xCrxTe

Magnetic and transport properties of an epitaxial film of ferromagnetic II–VI diluted magnetic semiconductor (DMS) Zn1−xCrxTe (x=0.035) were investigated. The Curie temperature TC of the film was about 15 K, which is the highest among the reported ferromagnetic II–IV DMS. Hall effect measurements at room temperature showed a hole concentration p of about 1×1015 cm−3, which is several orders lower than that reported for carrier-induced ferromagnetic Zn1−xMnxTe. These results suggest that a ferromagnetic superexchange interaction between Cr ions is responsible for the observed ferromagnetism in Zn1−xCrxTe.

Electronic States near the Fermi Level in the Antiferromagnetic and Ferromagnetic Spinels of Zn 1− x Cu x Cr 2 Se 4 ; 0.0 ≤ x ≤ 1.0

The electronic states of normal-type spinels in Zn 1 m x Cu x Cr 2 Se 4 have been studied by X-ray absorption spectroscopy near the K-edge of Zn, Cu, Cr and Se ions. It is found that characteristic white lines occur near the X-ray absorption threshold for Zn and Se ions, but not for Cu and Cr ions. It is also found that the white lines show a slight energy shift, which depends on the Cu concentration. The energy shifts mean that Fermi level gradually approaches the top region of the valence band of Se 2 m , on increasing the Cu ions. The substitution of Zn 2+ with Cu 1+ ions increases the number of positive carriers, holes. The holes occupying the top region of the valence band strongly correlate with Cr 4+ , which forms an empty orbital in the 3d-band of Cr 3+ and exchanges the valence electrons with Cr 3+ . It is interpreted that the ferromagnetism in Zn 1 m x Cu x Cr 2 Se 4 is made by double-exchange interaction between Cr 3+ and Cr 4+ ions and that holes contribute to the electronic conductivity of Zn 1 m x Cu x Cr 2 Se 4 .

Electronic structure of Zn1−xCuxCr2Se4

Some electronic properties of the metallic, ferromagnetic spinels Zn1−xCuxCr2Se4 are presented. The picture of the band structure for these solid solutions at T = 4.2 K is an extension of the Lotgering-Van Stapele model completed by a set of important exchange and band parameters, calculated with the help of the Stoner-Edwards-Wohlfarth theory. The main features of the band structure are: the wide conduction band is constructed from the 4s and 4p orbitals of Cu and Cr and the narrow d band of the delocalized d-electrons of the cations lies below it; the lower part of the valence band is dominantly constructed from the anion's p orbitals whereas the very narrow bands having mainly d-character range over the higher energy region of the valence band.