COMPOSITIONS AND MATERIALS FOR ELECTRONIC APPLICATIONS
Embodiments disclosed herein relate to using cobalt (Co) to fine tune the magnetic properties, such as permeability and magnetic loss, of nickel-zinc ferrites to improve the material performance in electronic applications. The method comprises replacing nickel (Ni) with sufficient Co +2 such that the relaxation peak associated with the Co +2 substitution and the relaxation peak associated with the nickel to zinc (Ni/Zn) ratio are into near coincidence. When the relaxation peaks overlap, the material permeability can be substantially maximized and magnetic loss substantially minimized. The resulting materials are useful and provide superior performance particularly for devices operating at the 13.56 MHz ISM band.
1 . A composition represented by the formula
Ni 1-w-x-y-z Zn w Co x Mn y Cu z Fe 2-a O 4-x wherein
w is greater than or equal to 0.2 and less than or equal to 0.6;
x is greater than or equal to 0 and less than or equal to 0.2;
y is greater than or equal to 0 and less than or equal to 0.2;
z is greater than or equal to 0 and less than or equal to 0.2; and
a is greater than or equal to 0 and less than or equal to 0.2.
2 . The composition of claim 1 wherein w=0, x=0.0225, y=0.02, z=0 and a=0.08.
3 . The composition of claim 1 wherein z=0.
4 . The composition of claim 1 wherein y=0.
5 . An RF device incorporating the composition of claim 1 , wherein the RF device operates in the 13.56 MHz band.
6 . An RF device incorporating the composition of claim 1 , wherein the RF device is an antenna.
7 . A modified nickel-zinc ferrite composition represented by the formula
NiZn (1-x) Co x Fe 2 O 4 , wherein
x is greater than or equal to 0.1 and less than or equal to 0.3.
8 . The composition of claim 7 wherein x is greater than or equal to 0.125 and less than or equal to 0.275.
9 . The composition of claim 7 wherein x is greater than or equal to 0.2 and less than or equal to 0.3.
10 . The composition of claim 7 wherein x is greater than or equal to 0.1 and less than or equal to 0.2.
11 . The composition of claim 7 wherein x is equal to 0.0225.
12 . The composition of claim 7 wherein x is greater than or equal to 0.175 and less than or equal to 0.3.
13 . An RF device incorporating the composition of claim 7 , wherein the RF device is selected from the group consisting of RFID tags, biomedical sensors, and RF antennas.
14 . A method of fine tuning nickel-zinc ferrite material, said method comprising:
adjusting the nickel to zinc ratio to provide a Ni/Zn relaxation absorption peak at a desired frequency above a desired low magnetic loss frequency; and
doping the material with cobalt (Co 2+ ) to a level where the cobalt dominated relaxation peak merges into the low frequency end of the Ni/Zn relaxation absorption peak.
15 . The method of claim 14 further comprises forming a part with the nickel to zinc ratio and Co concentration.
16 . The method of claim 15 further comprises sintering the part.
17 . The method of claim 14 wherein the part comprises an antenna adapted for RF devices.
18 . The method of claim 14 wherein the nickel to zinc ratio is 0.45 to 0.55.
19 . The method of claim 14 wherein the relaxation peak associated with the Co +2 doping and the relaxation peak associated with the nickel to zinc (Ni/Zn) ratio are into near coincidence.
20 . The method of claim 14 further comprises blending raw oxides NiO, Fe 2 O 3 , CoO x , MnO x , ZnO, and CuO x to form a mixture having the determined ratio of Ni to Zn and the determined Co concentration.