IEEE Transactions on Magnetics

This paper points out that the magnetic-phase transition and magnetocaloric effect of La0.7Ca0.3MnO3 (LCMO) can be easily controlled by using the mechanical milling method. Changing the milling time from 5 to 30 min, we have obtained LCMO nanoparticles (NPs) with average crystallite sizes (d, determined by the Williamson–Hall method) ranging from 100 to 45 nm. The magnetic studies (based on a superconducting quantum interference device) and simple analyses (based on Banerjee’s criteria) prove the magnetic-phase transformation from the first-order to the second-order, which takes place at a threshold value of d located in the range 60−70 nm. Compared with the as-prepared LCMO sample (a first-order magnetic phase transition), though the d decrease reduces the values of the T \(_{\mathrm {\textit{C}}}\) , magnetization, magnetic-entropy change, and refrigerant capacity, but the width of the magnetic phase transition is increased remarkably. This widens the working range of LCMO NPs in magnetic refrigeration applications. We believe that the presence of surface-related effects, lattice strain, and distortions leads to Mn3+–Mn4+ ferromagnetic interactions in LCMO NPs weaker than that in the as-prepared sample.

The modified Arrott plot method was used to analyze magnetic-field dependences of magnetization, \(M\) ( \(H\) ), for two polycrystalline samples Pr1-x Srx CoO3 with \(x = 0.4\) and 0.5. The analyses determined the values of critical parameters \(T_{C} \approx 204\) K, \(\beta = 0.654~\pm ~0.016\) , \(\gamma = 1.11~\pm ~0.009\) , and \(\delta = 2.70~\pm ~0.009\) for \(x = 0.4\) , and \(T_{C} \approx 218\) K, \(\beta = 0.495~\pm ~0.004\) , \(\gamma =0.991~\pm ~0.003\) , and \(\delta = 2.86~\pm ~0.009\) for \(x = 0.5\) . With these critical values, the \(M(H\) ) data around the \(T_{C}\) of the samples fall into two universal branches of a scaling function \(M(H\) , \(\varepsilon ) ={} \vert \varepsilon \vert ^{\beta }\!f_{\pm }\) ( \(H/ \vert \varepsilon \vert ^{\beta +\gamma }\) ), where \(\varepsilon =(T\) – \(T_{C}\) )/ \(T_{C}\) , and \(f_{+}\) for \(T > T_{C}\) and \(f_{-}\) for \(T < T_{C}\) . Here, the \(T_{C}\) increase with the increasing Sr content is ascribed to an increase of ferromagnetic (FM) double-exchange interaction pairs of Co3+–Co4+, and to the \(\beta \) change from 0.654 (for \(x = 0.4\) ) to 0.495 (for \(x = 0.5\) ). This corresponds to the change in FM interactions from short-range to nearly long-range FM orders. Based on the \(M(H)\) data, we also determined the magnetic-entropy change, which reaches a maximum value ( \(\vert \Delta S_{\max } \vert \) ) around the \(T_{C}\) ; \(\vert \Delta S_{\max } \vert \,\approx ~1.9\) and 2.2 J/kg \(\cdot \) K for \(x =0.4\) and 0.5, respectively, for a magnetic field change \(\Delta H = 50\) kOe. The relative cooling power thus increases from 52 J/kg (for \(x = 0.4\) ) to 84 J/kg (for \(x = 0.5\) ). In particular, field dependences of the magnetic-entropy change ( \(\Delta S_{m}\) ) obey a power function \(\vert\Delta S_{m}\) ( \(H\) ) \(\vert ~\propto H^{\mathbf {n}}\) , where the magnetic-ordering parameter ( \(n\) ) slightly decreases from 0.75 for \(x = 0.4\) to 0.70 for \(x = 0.5\) .

High frequency characteristics and mechanical properties of CuBe alloy pins are evaluated to meet the fast computer connector requirements. A new jig to measure the 1 MHz-1 GHz impedance of the pins is developed. The inductance and the cross-talk for CuBe pins were similar to those of phosphor bronze pins because both are non-magnetic materials. The feature of CuBe alloy pins are low ac resistance and good mechanical deflection properties in the case of short pins which is desirable for miniaturized connector development.

Recording results of write heads using sputtered laminated FeN/Al/sub 2/O/sub 3/ materials on thin film media with coercivity up to 3800 Oe are compared with those obtained using plated NiFe materials. The thickness of P2 (second pole) of FeN merged write heads is about 3.2 /spl mu/m, and those of plated NiFe heads, 3.5 and 6.3 /spl mu/m respectively. These heads have two write gap thickness, around 0.2 and 0.4 /spl mu/m. Various recording measurements show that these high magnetization FeN heads of 0.15 /spl mu/m gap write well on media of 3800 Oe, while the corresponding NiFe ones with a P2 of twice the thickness could not. For a wide 0.39 /spl mu/m gap, the FeN write heads still work well and the NiFe ones with twice the pole thickness, also did, but at reduced resolution, In short, write heads using a narrow gap and high magnetization materials such as FeN can write 3800 Oe coercivity media, which is capable of storing a bit density over 10 Gb/in/sup 2/.<>

In this paper, we have investigated the change in magnetization of multiferroic material, based on magnetic nanostructured CoFe/NiFe film grown on the piezoelectric lead zirconate titanate (PZT), under the effect of the strain originated from PZT layer. In this material, a converse magnetoelectric effect and especially, an electric field-induced magnetic anisotropy and magnetization switching process have been observed at the changing stages of applied electric voltage. In addition, a significant relative change in magnetization, above 100%, is obtained, which facilitates practical applications of the materials. This opens possibilities in achieving new types of memory devices, the low energy consumption devices, as well as other functionalities, such as voltage-tunable field sensing. A simple theory based on strain-mediated magnetic-electric coupling is also presented to understand the origin of the change in magnetic properties of the materials.