Zheng-zhong Li

Geometry dependence of the annealing effect on the magnetic properties of Fe48Co52 nanowire arrays

Highly ordered Fe48Co52 nanowire arrays with various interpore distances and diameters were fabricated by electrochemical deposition. The change of their magnetic properties after annealing has great dependences on the interpore distance and the wire diameter. The model of the prolate ellipsoid chain modified with the magnetostatic interaction is employed to explain this geometry dependence of the annealing effect. After annealing at 550 °C in H2 atmosphere, good hard magnetic properties (at room temperature, coercivity Hc = 3.89 kOe, squareness Mr/Ms = 0.954; at 78 K, Hc = 4.55 kOe, Mr/Ms = 0.954) were obtained in the arrays with a diameter of about 22 nm and an interpore distance of about 50 nm.

A kind of potential permanent magnet film

Fe48Co52 nanowire arrays with various diameters and interpore distances were fabricated by electrochemical deposition. The dependences of the permanent magnetic properties on the diameter and interpore distance of the nanowire were investigated. The magnetic dipolar interaction among nanowires was employed to explain the experimental results. After annealing at 550°C, the excellent permanent magnetic properties were obtained. The coercivity Hc is 3.99kOe, the squareness Mr∕Ms is 0.96, and the maximum energy product of the whole composite film (BH)mf is estimated to be 7.1MGOe, which avails Fe–Co nanowire arrays prospective as a kind of potential permanent magnet film.

Pressure effects on the curie temperature of the colossal magnetoresistance manganites

Abstract In this paper, we investigate the pressure effects on the Curie temperature ( T c ) of the colossal magnetoresistance manganites by introducing a pressure dependence of the Hunds rule coupling strength. It is shown that the pressure coefficient of T c is positive and descended with the increase of the nomial hole concentration which is qualitatively in agreement with the experiments.

Preparation of Ge quantum crystallites embedded in a-SiNx matrix by the PECVD method

Abstract Preparation of Ge quantum crystallites embedded in a-SiN x matrix was successfully achieved by the PECVD technique and followed thermal annealing treatment at 800°C. The microscopic heterogeneity of the as-deposited and thermal-annealed films were analyzed by the TEM and X-ray diffraction. We have found that substrate temperature is a critical parameter for the formation of Ge clusters. The temperature and time duration of annealing determine the size of Ge quantum crystallites. We are temporarily using the diffusion-limited growth model to explain the crystallization mechanism of this quantum material.

The coherent effect in the two-conduction-band heavy fermion alloy system

The specific heat coefficient and magnetic susceptibility for different concentrations of the heavy fermion alloy are calculated in the slave boson mean-field scheme. The results show that the system undergoes a smooth variation from incoherent dilute limit to the coherent dense limit as the concentration of the alloy increases from zero to unity.

Weak temperature dependence of angle-resolved photoemission within the periodic Anderson model

Abstract Within the framework of the periodic Anderson model, we have studied the angle-resolved photoemission spectroscopy of heavy-fermion systems by using the non-crossing approximation for lattice introduced by Grewe. It is found that the spectroscopy is weak temperature-dependent as well as dispersive at T>10 T K , which is in qualitative agreement with the experiments on single-crystalline samples.

Effect of conduction-band impurities on heavy-fermion systems

The effects of conduction-band (CB) impurities in heavy-fermion (HF) systems are investigated by introducing mixing disorder into the n-CB periodic Anderson model under the slave-boson mean-field theory. Within the single-site coherent-potential approximation, we find a mixing-renormalization treatment for the disorder. Its application to two-CB HF systems can qualitatively reproduce the experimental observations.

Theoretical investigation of the competition between the superconductivity and the ferromagnetism and the direction of the successive phase transition in itinerant ferromagnets

Abstract The competition between the superconductivity and the itinerant ferromagnetism and the direction of the successive phase transition are investigated by using a single-band model and the mean-field approximation. Taking into consideration the fact that the effective attraction and Coulomb repulsion exist in different energy regions, we calculate the free energy and the ferromagnetic and superconducting order parameters of the system considering that the effective attraction and Coulomb repulsion exist in the different energy regions. As a result, we show that only the successive phase transition (para normal → ferromagnetic → superconducting state on cooling) is possible for an itinerant system and that the successive phase transition (para normal → superconducting → ferromagnetic state) will never occur. This is in agreement with the experimental results for Y9Co7. Therefore, a more reasonable mean-field theory of the itinerant magnetic superconductor is provided in this article.