Magnetic field and gradient standards using permanent magnets: Design considerations, construction and validation by nuclear magnetic resonance

The construction and characterization of static magnetic density flux and gradient standards by using permanent magnets is presented. In the first case, the field homogeneity is high enough to be measured by a nuclear magnetic resonance magnetometer, confirming the traceability of the standard. In the second case, a gradient standard is shown. The experimental results obtained by Hall probes are in agreement with theoretical calculations. Designing considerations about materials choice and mounting are also addressed

On the specific absorption rate of hyperthermia fluids

The specific absorption rate (SAR) concept of hyperthermia ferrofluids is discussed. It is first suggested that SAR can be characterized at the steady state condition, taking into account the heating flow mechanism from the ferrofluid to the external environment. The temperature dependence of SAR is then addressed, indicating that the influence arises from both magnetic susceptibility and relaxation time of the system. At last, a single equation able to express the temperature versus time profile of a ferrofluid, when SAR is virtually temperature independent, is proposed up to the equilibrium condition

How Extrinsic Is the Coercivity in NdFeB Bonded Magnets?

The influence of the densification step, performed by uniaxial pressing at room temperature, on the coercivity of NdFeB bonded magnets has been analyzed. The mass density does not play any role on of non-cured magnets prepared by the mentioned method. Due to the brittle and intergranular character of the Nd Fe B-based phase fracture, the nano-sized grains are not affected or the modification is negligible, which maintains unchanged. After curing, the intrinsic coercivity of themagnets is reduced as a function of the compaction pressure increase

Stoner–Wohlfarth model for the anisotropic case

The Stoner–Wohlfarth (SW) model was calculated for the anisotropic case, by assuming crystallographical texture distributions as Gaussian, Lorentzian and cos n (alpha). All these distributions were tested and both Gaussian and cos n (alpha) give similar results for Mr/Ms above 0.8. However, the use of cosn (alpha) makes it easier to find analytical expressions representing texture.The Lorentzian distribution is a suitable choice for not wel laligned magnets, or magnets with a high fraction of misaligned grains. It is discussed how to obtain the alignment degree Mr/Ms directly from two measurements of magnetic remanence at the transverse and parallel directions to the alignment direction of the magnet .It is demonstrated that even the wel laligned magnets with Mr/Ms=0.96 present coercive field of 60–70% of the anisotropy field, depending on the chosen distribution.The anisotropic SW model was used for discussing hysteresis squareness. Improving the crystalographical texture, the loop squareness also increases

Fundamentals and advances in magnetic hyperthermia

Nowadays, magnetic hyperthermia constitutes a complementary approach to cancer treatment. The use of magnetic particles as heating mediators, proposed in the 1950s, provides a novel strategy for improving tumor treatment and, consequently, patient's quality of life. This review reports a broad overview about several aspects of magnetic hyperthermia addressing new perspectives and the progress on relevant features such as the ad hoc preparation of magnetic nanoparticles, physical modeling of magnetic heating, methods to determine the heat dissipation power of magnetic colloids including the development of experimental apparatus and the influence of biological matrices on the heating efficiency.Multifunctional Nanoparticles for Magnetic Hyperthermia and Indirect Radiation Therap